Post on 18-Feb-2016
description
Nikhil R Dhar Ph DProfessor IPE Department
BUET
IPE-3209 METAL FORMING AND
SHEET METALWORKING
Department of Industrial amp Production Engineering
Course Outlines
Fundamental of Metal Forming Overview of metal formingmaterial behavior in metal forming temperature in metal formingfriction and lubrication in metal forming
Bulk Deformation Processes in Metal Working
Rolling and Other deformation processes related to rolling
Forging and Other deformation processes related to forging
Extrusion and Other deformation processes related to forging
Sheet Metal Working Cutting operations bending operationsdrawing Other sheet metal forming operations precision formingprocesses various features of different types of metal forming diesprinciples of powder forming
1072
Department of Industrial amp Production Engineering
Suggested Reading
Manufacturing Processes for Engineering Materials - S Kalpakjianamp S R Schmid
Materials and Processes in Manufacturing - EP Degarmo JTBlack amp RA Kohser
Fundamentals of Modern Manufacturing - MP Groover
Processes and Design for Manufacturing - SDEI Wakil
Metal Cutting Principles - M C Shaw
Metal Cutting - E Trent
Manufacturing Technology ndash B Kumar
1073
Department of Industrial amp Production Engineering
Marks Distribution
Total Marks 100
Class Test (20)
Class Attendance[10]
Final Examination[70]
1 2 3 4
10 10 10 10 10 70
Quiz-01 Fundamental of Metal Forming
Quiz-02 Bulk Deformation Processes - Rolling
Quiz-03 Bulk Deformation Processes - Forging
Quiz-04 Sheet Metal Forming Processes
1074
Nikhil R Dhar Ph DProfessor IPE Department
BUET
LECTURE-01 FUNDAMENTAL OF
METAL FORMING
Department of Industrial amp Production Engineering
Introduction
Large group of manufacturing processes in which plastic deformation isused to change the shape of metal workpieces
The tool usually called a die applies stresses that exceed the yieldstrength of the metal
The metal takes a shape determined by the geometry of the die
Forming processes tend to be complex systems consisting
Independent Variables
Dependent Variables and
Independent-dependent Interrelations
1076
Department of Industrial amp Production Engineering
Independent Variables Independent variables are those aspects of theprocess over which the engineer has direct control and they are generallyselected or specified when setting up the process Consider some of theindependent variables in a typical forming process
Starting material The engineer is often free to specify the chemistryand condition These may also be chosen for ease in fabrication or theymay be restricted by the final properties desired for the product
Starting geometry of the workpiece This may be dictated by previousprocessing or it may be selected by the engineer from a variety ofavailable shapes Economics often influence this decision
Tool or die geometry This are has many aspects such as the diameterof a rolling mill roll the die angle in wire drawing and the cavitydetails when forging Since tooling will produce and control the metalflow success or failure of a process often depends on tool geometry
1077
Department of Industrial amp Production Engineering
Lubrication Since lubricants also acts as coolants thermal barrierscorrosion inhibitors and parting compounds their selection is anaspect of great importance Specification includes type of lubricantamount to be applied and the method of application
Starting temperature Many material properties vary greatly withtemperature so its selection and control may well dictate the successor failure of an operation
Speed of operation Since speed can directly influence the lubricanteffectiveness the forces required for deformation and the timeavailable for heat transfer It is obvious that its selection would besignificant in a forming operation
Amount of deformation While some processes control this variablethrough die design others such as rolling permits its selection at thediscretion of the engineer
1078
Department of Industrial amp Production Engineering
Dependent Variables After the engineer specifies the independentvariables the process then determine the nature and values for a second setof variables Known as dependent variables these in essence are theconsequences of the dependent variable selection Consider some of thedependent variables in a typical forming process
Force or power requirements Engineers cannot directly specify theforce or power they can only specify the independent variables andthen experience the consequences of the selection The ability topredict the forces or powers however is extremely important for onlyby having this knowledge will the engineer be able to specify or selectthe equipment for the process
Material properties of the product The customer is not interested inthe starting properties but is concerned with our ability to produce thedesired final shape with the desired final properties
1079
Department of Industrial amp Production Engineering
Exit (or Final) temperature Engineering properties can be altered byboth the mechanical and thermal history of the material thus it isimportant to know and control the temperature of the materialthroughout the process
Surface finish and precision Both are characteristics of the resultantproduct that are dependent on the specific details of the process
Nature of the material flow Since properties depend on deformationhistory control here is vital the customer is satisfied only if the desiredgeometric shape is produced with the right set of companion propertiesand without surface or internal defects
10710
Department of Industrial amp Production Engineering
Independent-Dependent Interrelations The following Figure illustrate a majorproblem facing the metal-forming engineer On one side are the independentvariables those aspect of the process for which control is direct and immediate Onthe other are the dependent variables those aspects for which control is totallyindirect It is the dependent variables that we want to control but the dependentvariables are determioned by the process as consequences of the independentvariable selection If we want to change a dependent variable we must determinewhich independent variable is to be changed in what manner and by how much Thusit is important for us to develop a knowledge of the independent variable-dependentvariable interrelations
details flow Material
precision lDimensiona
finish Surface
ratureExit tempe
propertiesProduct
trequiremenPower Forceor
Modeling
Experiment
Experience
ndeformatio ofAmount
ndeformatio of Speed
re temperatuStarting
nLubricatio
geometry Tool
geometry Starting
material Starting
variablesDependent variablest Independen
Schematic of the metal-forming systemshowing independent variablesdependent variables and the variousmeans of relating the two
10711
Department of Industrial amp Production Engineering
The ability to predict and control dependent variables can be obtained inthree distinct ways
Experience This requires long time exposure to the process and isgenerally limited to the specific materials equipment and productsencountered in the realm of past contact
Experiment While possibly the least likely in error direct experimentis both time consuming and costly
Process modeling Here one approaches the problem with a high speedcomputer and one or more mathematical models of the processnumerical values are provided for the various independent variablesand the models are used to compute predictions for the dependentvariables Most techniques rely on the applied theory of plasticity withvarious simplifying assumptions
10712
Department of Industrial amp Production Engineering
General Parameters
While much metal-forming knowledge is specific to a given process there arecertain features that are common to all processes and these will be presentedhere
Friction and Lubrication An important consideration in metaldeformation processes is the friction developed between the tool and theworkpiece For some processes more than 50 of the input energy isspent in overcoming friction The surface finish and dimensional precisionof the product are often directly related to friction Changes in lubricationcan alter the mode of material flow during forming and in so doing createor eliminate defects or modify the properties of the final productProduction rate tool design tool wear and process optimization alldepend on the ability to determine and control process friction
Temperature Concerns In general an increase in temperature brings outa decrease in strength an increase in ductility and a decrease in the rateof strain hardening - all effects that would tend to promote ease ofdeformation
10713
Department of Industrial amp Production Engineering
Forming processes tend to be classified as hot working cold working or warmworking based on both the temperature and the material being formed
Hot Working
Elevated temperatures bring about a decrease in the yield strength of ametal and an increase in ductility At the temperatures of hot workingrecrystallization eliminates the effects of strain hardening so there isno significant increase in yield strength or hardness or correspondingdecrease in ductility
The plastic deformation of metals above their recrystallizationtemperature it is important to note however that the recrystallizationtemperature varies greatly with different materials
In addition the elevated temperatures promote diffusion that canremove or reduce chemical inhomogeneities pores can be welded shutor reduced in size during the deformation and the metallurgicalstructure can often be altered through recrystallization to improve thefinal properties
10714
Department of Industrial amp Production Engineering
Structure and Property Modification by Hot Working When metalssolidify particularly in the large sections that are typical cast strandscoarse structures tend to form with a certain amount of chemicalsegregation The size of the grains is usually not uniform andundesirable grain shapes can be quite common such as the columnargrains Small gas cavities or shrinkage porosity can also form duringsolidification
Temperature Variations The success or failure of a hot deformationprocess often depends on the ability to control the temperatures withthe workpiece To minimize problems it is desirable to keep theworkpiece temperatures as uniform as possible
Cold Working
Plastic deformation of metals below the recrystallization temperatureis known as cold working The process is usually performed at roomtemperature but mildly elevated temperatures may be used to provideincreased ductility and reduced strength
10715
Department of Industrial amp Production Engineering
Advantages of cold working No heating is required Strength fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved so little if any secondary machining
is required Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized
Disadvantages of cold working Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility
that accompanies strain hardening Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free Imparted directional properties may be detrimental Undesirable residual stresses may be produced
10716
Department of Industrial amp Production Engineering
Warm Working
Deformation produced at temperatures intermediate to hot and coldworking
Compared to cold working it offers the advantages of reduced loads on thetooling and equipment increased material ductility and a possiblereduction in the number of anneals due to a reduction in the amount ofstrain hardening
Compared to hot forming the lower temperatures of warm workingproduce less scaling and decarburization and enable production ofproducts with better dimensional precision and smoother surfaces
The warm regime generally requires less energy than hot working due tothe decreased energy in heating the workpiece energy saved throughhigher precision and the possible elimination of post forming heattreatments
Tools last longer for while they must exert 25 to 60 higher forces thereis less thermal shock and thermal fatigue
10717
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Course Outlines
Fundamental of Metal Forming Overview of metal formingmaterial behavior in metal forming temperature in metal formingfriction and lubrication in metal forming
Bulk Deformation Processes in Metal Working
Rolling and Other deformation processes related to rolling
Forging and Other deformation processes related to forging
Extrusion and Other deformation processes related to forging
Sheet Metal Working Cutting operations bending operationsdrawing Other sheet metal forming operations precision formingprocesses various features of different types of metal forming diesprinciples of powder forming
1072
Department of Industrial amp Production Engineering
Suggested Reading
Manufacturing Processes for Engineering Materials - S Kalpakjianamp S R Schmid
Materials and Processes in Manufacturing - EP Degarmo JTBlack amp RA Kohser
Fundamentals of Modern Manufacturing - MP Groover
Processes and Design for Manufacturing - SDEI Wakil
Metal Cutting Principles - M C Shaw
Metal Cutting - E Trent
Manufacturing Technology ndash B Kumar
1073
Department of Industrial amp Production Engineering
Marks Distribution
Total Marks 100
Class Test (20)
Class Attendance[10]
Final Examination[70]
1 2 3 4
10 10 10 10 10 70
Quiz-01 Fundamental of Metal Forming
Quiz-02 Bulk Deformation Processes - Rolling
Quiz-03 Bulk Deformation Processes - Forging
Quiz-04 Sheet Metal Forming Processes
1074
Nikhil R Dhar Ph DProfessor IPE Department
BUET
LECTURE-01 FUNDAMENTAL OF
METAL FORMING
Department of Industrial amp Production Engineering
Introduction
Large group of manufacturing processes in which plastic deformation isused to change the shape of metal workpieces
The tool usually called a die applies stresses that exceed the yieldstrength of the metal
The metal takes a shape determined by the geometry of the die
Forming processes tend to be complex systems consisting
Independent Variables
Dependent Variables and
Independent-dependent Interrelations
1076
Department of Industrial amp Production Engineering
Independent Variables Independent variables are those aspects of theprocess over which the engineer has direct control and they are generallyselected or specified when setting up the process Consider some of theindependent variables in a typical forming process
Starting material The engineer is often free to specify the chemistryand condition These may also be chosen for ease in fabrication or theymay be restricted by the final properties desired for the product
Starting geometry of the workpiece This may be dictated by previousprocessing or it may be selected by the engineer from a variety ofavailable shapes Economics often influence this decision
Tool or die geometry This are has many aspects such as the diameterof a rolling mill roll the die angle in wire drawing and the cavitydetails when forging Since tooling will produce and control the metalflow success or failure of a process often depends on tool geometry
1077
Department of Industrial amp Production Engineering
Lubrication Since lubricants also acts as coolants thermal barrierscorrosion inhibitors and parting compounds their selection is anaspect of great importance Specification includes type of lubricantamount to be applied and the method of application
Starting temperature Many material properties vary greatly withtemperature so its selection and control may well dictate the successor failure of an operation
Speed of operation Since speed can directly influence the lubricanteffectiveness the forces required for deformation and the timeavailable for heat transfer It is obvious that its selection would besignificant in a forming operation
Amount of deformation While some processes control this variablethrough die design others such as rolling permits its selection at thediscretion of the engineer
1078
Department of Industrial amp Production Engineering
Dependent Variables After the engineer specifies the independentvariables the process then determine the nature and values for a second setof variables Known as dependent variables these in essence are theconsequences of the dependent variable selection Consider some of thedependent variables in a typical forming process
Force or power requirements Engineers cannot directly specify theforce or power they can only specify the independent variables andthen experience the consequences of the selection The ability topredict the forces or powers however is extremely important for onlyby having this knowledge will the engineer be able to specify or selectthe equipment for the process
Material properties of the product The customer is not interested inthe starting properties but is concerned with our ability to produce thedesired final shape with the desired final properties
1079
Department of Industrial amp Production Engineering
Exit (or Final) temperature Engineering properties can be altered byboth the mechanical and thermal history of the material thus it isimportant to know and control the temperature of the materialthroughout the process
Surface finish and precision Both are characteristics of the resultantproduct that are dependent on the specific details of the process
Nature of the material flow Since properties depend on deformationhistory control here is vital the customer is satisfied only if the desiredgeometric shape is produced with the right set of companion propertiesand without surface or internal defects
10710
Department of Industrial amp Production Engineering
Independent-Dependent Interrelations The following Figure illustrate a majorproblem facing the metal-forming engineer On one side are the independentvariables those aspect of the process for which control is direct and immediate Onthe other are the dependent variables those aspects for which control is totallyindirect It is the dependent variables that we want to control but the dependentvariables are determioned by the process as consequences of the independentvariable selection If we want to change a dependent variable we must determinewhich independent variable is to be changed in what manner and by how much Thusit is important for us to develop a knowledge of the independent variable-dependentvariable interrelations
details flow Material
precision lDimensiona
finish Surface
ratureExit tempe
propertiesProduct
trequiremenPower Forceor
Modeling
Experiment
Experience
ndeformatio ofAmount
ndeformatio of Speed
re temperatuStarting
nLubricatio
geometry Tool
geometry Starting
material Starting
variablesDependent variablest Independen
Schematic of the metal-forming systemshowing independent variablesdependent variables and the variousmeans of relating the two
10711
Department of Industrial amp Production Engineering
The ability to predict and control dependent variables can be obtained inthree distinct ways
Experience This requires long time exposure to the process and isgenerally limited to the specific materials equipment and productsencountered in the realm of past contact
Experiment While possibly the least likely in error direct experimentis both time consuming and costly
Process modeling Here one approaches the problem with a high speedcomputer and one or more mathematical models of the processnumerical values are provided for the various independent variablesand the models are used to compute predictions for the dependentvariables Most techniques rely on the applied theory of plasticity withvarious simplifying assumptions
10712
Department of Industrial amp Production Engineering
General Parameters
While much metal-forming knowledge is specific to a given process there arecertain features that are common to all processes and these will be presentedhere
Friction and Lubrication An important consideration in metaldeformation processes is the friction developed between the tool and theworkpiece For some processes more than 50 of the input energy isspent in overcoming friction The surface finish and dimensional precisionof the product are often directly related to friction Changes in lubricationcan alter the mode of material flow during forming and in so doing createor eliminate defects or modify the properties of the final productProduction rate tool design tool wear and process optimization alldepend on the ability to determine and control process friction
Temperature Concerns In general an increase in temperature brings outa decrease in strength an increase in ductility and a decrease in the rateof strain hardening - all effects that would tend to promote ease ofdeformation
10713
Department of Industrial amp Production Engineering
Forming processes tend to be classified as hot working cold working or warmworking based on both the temperature and the material being formed
Hot Working
Elevated temperatures bring about a decrease in the yield strength of ametal and an increase in ductility At the temperatures of hot workingrecrystallization eliminates the effects of strain hardening so there isno significant increase in yield strength or hardness or correspondingdecrease in ductility
The plastic deformation of metals above their recrystallizationtemperature it is important to note however that the recrystallizationtemperature varies greatly with different materials
In addition the elevated temperatures promote diffusion that canremove or reduce chemical inhomogeneities pores can be welded shutor reduced in size during the deformation and the metallurgicalstructure can often be altered through recrystallization to improve thefinal properties
10714
Department of Industrial amp Production Engineering
Structure and Property Modification by Hot Working When metalssolidify particularly in the large sections that are typical cast strandscoarse structures tend to form with a certain amount of chemicalsegregation The size of the grains is usually not uniform andundesirable grain shapes can be quite common such as the columnargrains Small gas cavities or shrinkage porosity can also form duringsolidification
Temperature Variations The success or failure of a hot deformationprocess often depends on the ability to control the temperatures withthe workpiece To minimize problems it is desirable to keep theworkpiece temperatures as uniform as possible
Cold Working
Plastic deformation of metals below the recrystallization temperatureis known as cold working The process is usually performed at roomtemperature but mildly elevated temperatures may be used to provideincreased ductility and reduced strength
10715
Department of Industrial amp Production Engineering
Advantages of cold working No heating is required Strength fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved so little if any secondary machining
is required Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized
Disadvantages of cold working Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility
that accompanies strain hardening Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free Imparted directional properties may be detrimental Undesirable residual stresses may be produced
10716
Department of Industrial amp Production Engineering
Warm Working
Deformation produced at temperatures intermediate to hot and coldworking
Compared to cold working it offers the advantages of reduced loads on thetooling and equipment increased material ductility and a possiblereduction in the number of anneals due to a reduction in the amount ofstrain hardening
Compared to hot forming the lower temperatures of warm workingproduce less scaling and decarburization and enable production ofproducts with better dimensional precision and smoother surfaces
The warm regime generally requires less energy than hot working due tothe decreased energy in heating the workpiece energy saved throughhigher precision and the possible elimination of post forming heattreatments
Tools last longer for while they must exert 25 to 60 higher forces thereis less thermal shock and thermal fatigue
10717
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Suggested Reading
Manufacturing Processes for Engineering Materials - S Kalpakjianamp S R Schmid
Materials and Processes in Manufacturing - EP Degarmo JTBlack amp RA Kohser
Fundamentals of Modern Manufacturing - MP Groover
Processes and Design for Manufacturing - SDEI Wakil
Metal Cutting Principles - M C Shaw
Metal Cutting - E Trent
Manufacturing Technology ndash B Kumar
1073
Department of Industrial amp Production Engineering
Marks Distribution
Total Marks 100
Class Test (20)
Class Attendance[10]
Final Examination[70]
1 2 3 4
10 10 10 10 10 70
Quiz-01 Fundamental of Metal Forming
Quiz-02 Bulk Deformation Processes - Rolling
Quiz-03 Bulk Deformation Processes - Forging
Quiz-04 Sheet Metal Forming Processes
1074
Nikhil R Dhar Ph DProfessor IPE Department
BUET
LECTURE-01 FUNDAMENTAL OF
METAL FORMING
Department of Industrial amp Production Engineering
Introduction
Large group of manufacturing processes in which plastic deformation isused to change the shape of metal workpieces
The tool usually called a die applies stresses that exceed the yieldstrength of the metal
The metal takes a shape determined by the geometry of the die
Forming processes tend to be complex systems consisting
Independent Variables
Dependent Variables and
Independent-dependent Interrelations
1076
Department of Industrial amp Production Engineering
Independent Variables Independent variables are those aspects of theprocess over which the engineer has direct control and they are generallyselected or specified when setting up the process Consider some of theindependent variables in a typical forming process
Starting material The engineer is often free to specify the chemistryand condition These may also be chosen for ease in fabrication or theymay be restricted by the final properties desired for the product
Starting geometry of the workpiece This may be dictated by previousprocessing or it may be selected by the engineer from a variety ofavailable shapes Economics often influence this decision
Tool or die geometry This are has many aspects such as the diameterof a rolling mill roll the die angle in wire drawing and the cavitydetails when forging Since tooling will produce and control the metalflow success or failure of a process often depends on tool geometry
1077
Department of Industrial amp Production Engineering
Lubrication Since lubricants also acts as coolants thermal barrierscorrosion inhibitors and parting compounds their selection is anaspect of great importance Specification includes type of lubricantamount to be applied and the method of application
Starting temperature Many material properties vary greatly withtemperature so its selection and control may well dictate the successor failure of an operation
Speed of operation Since speed can directly influence the lubricanteffectiveness the forces required for deformation and the timeavailable for heat transfer It is obvious that its selection would besignificant in a forming operation
Amount of deformation While some processes control this variablethrough die design others such as rolling permits its selection at thediscretion of the engineer
1078
Department of Industrial amp Production Engineering
Dependent Variables After the engineer specifies the independentvariables the process then determine the nature and values for a second setof variables Known as dependent variables these in essence are theconsequences of the dependent variable selection Consider some of thedependent variables in a typical forming process
Force or power requirements Engineers cannot directly specify theforce or power they can only specify the independent variables andthen experience the consequences of the selection The ability topredict the forces or powers however is extremely important for onlyby having this knowledge will the engineer be able to specify or selectthe equipment for the process
Material properties of the product The customer is not interested inthe starting properties but is concerned with our ability to produce thedesired final shape with the desired final properties
1079
Department of Industrial amp Production Engineering
Exit (or Final) temperature Engineering properties can be altered byboth the mechanical and thermal history of the material thus it isimportant to know and control the temperature of the materialthroughout the process
Surface finish and precision Both are characteristics of the resultantproduct that are dependent on the specific details of the process
Nature of the material flow Since properties depend on deformationhistory control here is vital the customer is satisfied only if the desiredgeometric shape is produced with the right set of companion propertiesand without surface or internal defects
10710
Department of Industrial amp Production Engineering
Independent-Dependent Interrelations The following Figure illustrate a majorproblem facing the metal-forming engineer On one side are the independentvariables those aspect of the process for which control is direct and immediate Onthe other are the dependent variables those aspects for which control is totallyindirect It is the dependent variables that we want to control but the dependentvariables are determioned by the process as consequences of the independentvariable selection If we want to change a dependent variable we must determinewhich independent variable is to be changed in what manner and by how much Thusit is important for us to develop a knowledge of the independent variable-dependentvariable interrelations
details flow Material
precision lDimensiona
finish Surface
ratureExit tempe
propertiesProduct
trequiremenPower Forceor
Modeling
Experiment
Experience
ndeformatio ofAmount
ndeformatio of Speed
re temperatuStarting
nLubricatio
geometry Tool
geometry Starting
material Starting
variablesDependent variablest Independen
Schematic of the metal-forming systemshowing independent variablesdependent variables and the variousmeans of relating the two
10711
Department of Industrial amp Production Engineering
The ability to predict and control dependent variables can be obtained inthree distinct ways
Experience This requires long time exposure to the process and isgenerally limited to the specific materials equipment and productsencountered in the realm of past contact
Experiment While possibly the least likely in error direct experimentis both time consuming and costly
Process modeling Here one approaches the problem with a high speedcomputer and one or more mathematical models of the processnumerical values are provided for the various independent variablesand the models are used to compute predictions for the dependentvariables Most techniques rely on the applied theory of plasticity withvarious simplifying assumptions
10712
Department of Industrial amp Production Engineering
General Parameters
While much metal-forming knowledge is specific to a given process there arecertain features that are common to all processes and these will be presentedhere
Friction and Lubrication An important consideration in metaldeformation processes is the friction developed between the tool and theworkpiece For some processes more than 50 of the input energy isspent in overcoming friction The surface finish and dimensional precisionof the product are often directly related to friction Changes in lubricationcan alter the mode of material flow during forming and in so doing createor eliminate defects or modify the properties of the final productProduction rate tool design tool wear and process optimization alldepend on the ability to determine and control process friction
Temperature Concerns In general an increase in temperature brings outa decrease in strength an increase in ductility and a decrease in the rateof strain hardening - all effects that would tend to promote ease ofdeformation
10713
Department of Industrial amp Production Engineering
Forming processes tend to be classified as hot working cold working or warmworking based on both the temperature and the material being formed
Hot Working
Elevated temperatures bring about a decrease in the yield strength of ametal and an increase in ductility At the temperatures of hot workingrecrystallization eliminates the effects of strain hardening so there isno significant increase in yield strength or hardness or correspondingdecrease in ductility
The plastic deformation of metals above their recrystallizationtemperature it is important to note however that the recrystallizationtemperature varies greatly with different materials
In addition the elevated temperatures promote diffusion that canremove or reduce chemical inhomogeneities pores can be welded shutor reduced in size during the deformation and the metallurgicalstructure can often be altered through recrystallization to improve thefinal properties
10714
Department of Industrial amp Production Engineering
Structure and Property Modification by Hot Working When metalssolidify particularly in the large sections that are typical cast strandscoarse structures tend to form with a certain amount of chemicalsegregation The size of the grains is usually not uniform andundesirable grain shapes can be quite common such as the columnargrains Small gas cavities or shrinkage porosity can also form duringsolidification
Temperature Variations The success or failure of a hot deformationprocess often depends on the ability to control the temperatures withthe workpiece To minimize problems it is desirable to keep theworkpiece temperatures as uniform as possible
Cold Working
Plastic deformation of metals below the recrystallization temperatureis known as cold working The process is usually performed at roomtemperature but mildly elevated temperatures may be used to provideincreased ductility and reduced strength
10715
Department of Industrial amp Production Engineering
Advantages of cold working No heating is required Strength fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved so little if any secondary machining
is required Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized
Disadvantages of cold working Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility
that accompanies strain hardening Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free Imparted directional properties may be detrimental Undesirable residual stresses may be produced
10716
Department of Industrial amp Production Engineering
Warm Working
Deformation produced at temperatures intermediate to hot and coldworking
Compared to cold working it offers the advantages of reduced loads on thetooling and equipment increased material ductility and a possiblereduction in the number of anneals due to a reduction in the amount ofstrain hardening
Compared to hot forming the lower temperatures of warm workingproduce less scaling and decarburization and enable production ofproducts with better dimensional precision and smoother surfaces
The warm regime generally requires less energy than hot working due tothe decreased energy in heating the workpiece energy saved throughhigher precision and the possible elimination of post forming heattreatments
Tools last longer for while they must exert 25 to 60 higher forces thereis less thermal shock and thermal fatigue
10717
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Marks Distribution
Total Marks 100
Class Test (20)
Class Attendance[10]
Final Examination[70]
1 2 3 4
10 10 10 10 10 70
Quiz-01 Fundamental of Metal Forming
Quiz-02 Bulk Deformation Processes - Rolling
Quiz-03 Bulk Deformation Processes - Forging
Quiz-04 Sheet Metal Forming Processes
1074
Nikhil R Dhar Ph DProfessor IPE Department
BUET
LECTURE-01 FUNDAMENTAL OF
METAL FORMING
Department of Industrial amp Production Engineering
Introduction
Large group of manufacturing processes in which plastic deformation isused to change the shape of metal workpieces
The tool usually called a die applies stresses that exceed the yieldstrength of the metal
The metal takes a shape determined by the geometry of the die
Forming processes tend to be complex systems consisting
Independent Variables
Dependent Variables and
Independent-dependent Interrelations
1076
Department of Industrial amp Production Engineering
Independent Variables Independent variables are those aspects of theprocess over which the engineer has direct control and they are generallyselected or specified when setting up the process Consider some of theindependent variables in a typical forming process
Starting material The engineer is often free to specify the chemistryand condition These may also be chosen for ease in fabrication or theymay be restricted by the final properties desired for the product
Starting geometry of the workpiece This may be dictated by previousprocessing or it may be selected by the engineer from a variety ofavailable shapes Economics often influence this decision
Tool or die geometry This are has many aspects such as the diameterof a rolling mill roll the die angle in wire drawing and the cavitydetails when forging Since tooling will produce and control the metalflow success or failure of a process often depends on tool geometry
1077
Department of Industrial amp Production Engineering
Lubrication Since lubricants also acts as coolants thermal barrierscorrosion inhibitors and parting compounds their selection is anaspect of great importance Specification includes type of lubricantamount to be applied and the method of application
Starting temperature Many material properties vary greatly withtemperature so its selection and control may well dictate the successor failure of an operation
Speed of operation Since speed can directly influence the lubricanteffectiveness the forces required for deformation and the timeavailable for heat transfer It is obvious that its selection would besignificant in a forming operation
Amount of deformation While some processes control this variablethrough die design others such as rolling permits its selection at thediscretion of the engineer
1078
Department of Industrial amp Production Engineering
Dependent Variables After the engineer specifies the independentvariables the process then determine the nature and values for a second setof variables Known as dependent variables these in essence are theconsequences of the dependent variable selection Consider some of thedependent variables in a typical forming process
Force or power requirements Engineers cannot directly specify theforce or power they can only specify the independent variables andthen experience the consequences of the selection The ability topredict the forces or powers however is extremely important for onlyby having this knowledge will the engineer be able to specify or selectthe equipment for the process
Material properties of the product The customer is not interested inthe starting properties but is concerned with our ability to produce thedesired final shape with the desired final properties
1079
Department of Industrial amp Production Engineering
Exit (or Final) temperature Engineering properties can be altered byboth the mechanical and thermal history of the material thus it isimportant to know and control the temperature of the materialthroughout the process
Surface finish and precision Both are characteristics of the resultantproduct that are dependent on the specific details of the process
Nature of the material flow Since properties depend on deformationhistory control here is vital the customer is satisfied only if the desiredgeometric shape is produced with the right set of companion propertiesand without surface or internal defects
10710
Department of Industrial amp Production Engineering
Independent-Dependent Interrelations The following Figure illustrate a majorproblem facing the metal-forming engineer On one side are the independentvariables those aspect of the process for which control is direct and immediate Onthe other are the dependent variables those aspects for which control is totallyindirect It is the dependent variables that we want to control but the dependentvariables are determioned by the process as consequences of the independentvariable selection If we want to change a dependent variable we must determinewhich independent variable is to be changed in what manner and by how much Thusit is important for us to develop a knowledge of the independent variable-dependentvariable interrelations
details flow Material
precision lDimensiona
finish Surface
ratureExit tempe
propertiesProduct
trequiremenPower Forceor
Modeling
Experiment
Experience
ndeformatio ofAmount
ndeformatio of Speed
re temperatuStarting
nLubricatio
geometry Tool
geometry Starting
material Starting
variablesDependent variablest Independen
Schematic of the metal-forming systemshowing independent variablesdependent variables and the variousmeans of relating the two
10711
Department of Industrial amp Production Engineering
The ability to predict and control dependent variables can be obtained inthree distinct ways
Experience This requires long time exposure to the process and isgenerally limited to the specific materials equipment and productsencountered in the realm of past contact
Experiment While possibly the least likely in error direct experimentis both time consuming and costly
Process modeling Here one approaches the problem with a high speedcomputer and one or more mathematical models of the processnumerical values are provided for the various independent variablesand the models are used to compute predictions for the dependentvariables Most techniques rely on the applied theory of plasticity withvarious simplifying assumptions
10712
Department of Industrial amp Production Engineering
General Parameters
While much metal-forming knowledge is specific to a given process there arecertain features that are common to all processes and these will be presentedhere
Friction and Lubrication An important consideration in metaldeformation processes is the friction developed between the tool and theworkpiece For some processes more than 50 of the input energy isspent in overcoming friction The surface finish and dimensional precisionof the product are often directly related to friction Changes in lubricationcan alter the mode of material flow during forming and in so doing createor eliminate defects or modify the properties of the final productProduction rate tool design tool wear and process optimization alldepend on the ability to determine and control process friction
Temperature Concerns In general an increase in temperature brings outa decrease in strength an increase in ductility and a decrease in the rateof strain hardening - all effects that would tend to promote ease ofdeformation
10713
Department of Industrial amp Production Engineering
Forming processes tend to be classified as hot working cold working or warmworking based on both the temperature and the material being formed
Hot Working
Elevated temperatures bring about a decrease in the yield strength of ametal and an increase in ductility At the temperatures of hot workingrecrystallization eliminates the effects of strain hardening so there isno significant increase in yield strength or hardness or correspondingdecrease in ductility
The plastic deformation of metals above their recrystallizationtemperature it is important to note however that the recrystallizationtemperature varies greatly with different materials
In addition the elevated temperatures promote diffusion that canremove or reduce chemical inhomogeneities pores can be welded shutor reduced in size during the deformation and the metallurgicalstructure can often be altered through recrystallization to improve thefinal properties
10714
Department of Industrial amp Production Engineering
Structure and Property Modification by Hot Working When metalssolidify particularly in the large sections that are typical cast strandscoarse structures tend to form with a certain amount of chemicalsegregation The size of the grains is usually not uniform andundesirable grain shapes can be quite common such as the columnargrains Small gas cavities or shrinkage porosity can also form duringsolidification
Temperature Variations The success or failure of a hot deformationprocess often depends on the ability to control the temperatures withthe workpiece To minimize problems it is desirable to keep theworkpiece temperatures as uniform as possible
Cold Working
Plastic deformation of metals below the recrystallization temperatureis known as cold working The process is usually performed at roomtemperature but mildly elevated temperatures may be used to provideincreased ductility and reduced strength
10715
Department of Industrial amp Production Engineering
Advantages of cold working No heating is required Strength fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved so little if any secondary machining
is required Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized
Disadvantages of cold working Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility
that accompanies strain hardening Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free Imparted directional properties may be detrimental Undesirable residual stresses may be produced
10716
Department of Industrial amp Production Engineering
Warm Working
Deformation produced at temperatures intermediate to hot and coldworking
Compared to cold working it offers the advantages of reduced loads on thetooling and equipment increased material ductility and a possiblereduction in the number of anneals due to a reduction in the amount ofstrain hardening
Compared to hot forming the lower temperatures of warm workingproduce less scaling and decarburization and enable production ofproducts with better dimensional precision and smoother surfaces
The warm regime generally requires less energy than hot working due tothe decreased energy in heating the workpiece energy saved throughhigher precision and the possible elimination of post forming heattreatments
Tools last longer for while they must exert 25 to 60 higher forces thereis less thermal shock and thermal fatigue
10717
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
LECTURE-01 FUNDAMENTAL OF
METAL FORMING
Department of Industrial amp Production Engineering
Introduction
Large group of manufacturing processes in which plastic deformation isused to change the shape of metal workpieces
The tool usually called a die applies stresses that exceed the yieldstrength of the metal
The metal takes a shape determined by the geometry of the die
Forming processes tend to be complex systems consisting
Independent Variables
Dependent Variables and
Independent-dependent Interrelations
1076
Department of Industrial amp Production Engineering
Independent Variables Independent variables are those aspects of theprocess over which the engineer has direct control and they are generallyselected or specified when setting up the process Consider some of theindependent variables in a typical forming process
Starting material The engineer is often free to specify the chemistryand condition These may also be chosen for ease in fabrication or theymay be restricted by the final properties desired for the product
Starting geometry of the workpiece This may be dictated by previousprocessing or it may be selected by the engineer from a variety ofavailable shapes Economics often influence this decision
Tool or die geometry This are has many aspects such as the diameterof a rolling mill roll the die angle in wire drawing and the cavitydetails when forging Since tooling will produce and control the metalflow success or failure of a process often depends on tool geometry
1077
Department of Industrial amp Production Engineering
Lubrication Since lubricants also acts as coolants thermal barrierscorrosion inhibitors and parting compounds their selection is anaspect of great importance Specification includes type of lubricantamount to be applied and the method of application
Starting temperature Many material properties vary greatly withtemperature so its selection and control may well dictate the successor failure of an operation
Speed of operation Since speed can directly influence the lubricanteffectiveness the forces required for deformation and the timeavailable for heat transfer It is obvious that its selection would besignificant in a forming operation
Amount of deformation While some processes control this variablethrough die design others such as rolling permits its selection at thediscretion of the engineer
1078
Department of Industrial amp Production Engineering
Dependent Variables After the engineer specifies the independentvariables the process then determine the nature and values for a second setof variables Known as dependent variables these in essence are theconsequences of the dependent variable selection Consider some of thedependent variables in a typical forming process
Force or power requirements Engineers cannot directly specify theforce or power they can only specify the independent variables andthen experience the consequences of the selection The ability topredict the forces or powers however is extremely important for onlyby having this knowledge will the engineer be able to specify or selectthe equipment for the process
Material properties of the product The customer is not interested inthe starting properties but is concerned with our ability to produce thedesired final shape with the desired final properties
1079
Department of Industrial amp Production Engineering
Exit (or Final) temperature Engineering properties can be altered byboth the mechanical and thermal history of the material thus it isimportant to know and control the temperature of the materialthroughout the process
Surface finish and precision Both are characteristics of the resultantproduct that are dependent on the specific details of the process
Nature of the material flow Since properties depend on deformationhistory control here is vital the customer is satisfied only if the desiredgeometric shape is produced with the right set of companion propertiesand without surface or internal defects
10710
Department of Industrial amp Production Engineering
Independent-Dependent Interrelations The following Figure illustrate a majorproblem facing the metal-forming engineer On one side are the independentvariables those aspect of the process for which control is direct and immediate Onthe other are the dependent variables those aspects for which control is totallyindirect It is the dependent variables that we want to control but the dependentvariables are determioned by the process as consequences of the independentvariable selection If we want to change a dependent variable we must determinewhich independent variable is to be changed in what manner and by how much Thusit is important for us to develop a knowledge of the independent variable-dependentvariable interrelations
details flow Material
precision lDimensiona
finish Surface
ratureExit tempe
propertiesProduct
trequiremenPower Forceor
Modeling
Experiment
Experience
ndeformatio ofAmount
ndeformatio of Speed
re temperatuStarting
nLubricatio
geometry Tool
geometry Starting
material Starting
variablesDependent variablest Independen
Schematic of the metal-forming systemshowing independent variablesdependent variables and the variousmeans of relating the two
10711
Department of Industrial amp Production Engineering
The ability to predict and control dependent variables can be obtained inthree distinct ways
Experience This requires long time exposure to the process and isgenerally limited to the specific materials equipment and productsencountered in the realm of past contact
Experiment While possibly the least likely in error direct experimentis both time consuming and costly
Process modeling Here one approaches the problem with a high speedcomputer and one or more mathematical models of the processnumerical values are provided for the various independent variablesand the models are used to compute predictions for the dependentvariables Most techniques rely on the applied theory of plasticity withvarious simplifying assumptions
10712
Department of Industrial amp Production Engineering
General Parameters
While much metal-forming knowledge is specific to a given process there arecertain features that are common to all processes and these will be presentedhere
Friction and Lubrication An important consideration in metaldeformation processes is the friction developed between the tool and theworkpiece For some processes more than 50 of the input energy isspent in overcoming friction The surface finish and dimensional precisionof the product are often directly related to friction Changes in lubricationcan alter the mode of material flow during forming and in so doing createor eliminate defects or modify the properties of the final productProduction rate tool design tool wear and process optimization alldepend on the ability to determine and control process friction
Temperature Concerns In general an increase in temperature brings outa decrease in strength an increase in ductility and a decrease in the rateof strain hardening - all effects that would tend to promote ease ofdeformation
10713
Department of Industrial amp Production Engineering
Forming processes tend to be classified as hot working cold working or warmworking based on both the temperature and the material being formed
Hot Working
Elevated temperatures bring about a decrease in the yield strength of ametal and an increase in ductility At the temperatures of hot workingrecrystallization eliminates the effects of strain hardening so there isno significant increase in yield strength or hardness or correspondingdecrease in ductility
The plastic deformation of metals above their recrystallizationtemperature it is important to note however that the recrystallizationtemperature varies greatly with different materials
In addition the elevated temperatures promote diffusion that canremove or reduce chemical inhomogeneities pores can be welded shutor reduced in size during the deformation and the metallurgicalstructure can often be altered through recrystallization to improve thefinal properties
10714
Department of Industrial amp Production Engineering
Structure and Property Modification by Hot Working When metalssolidify particularly in the large sections that are typical cast strandscoarse structures tend to form with a certain amount of chemicalsegregation The size of the grains is usually not uniform andundesirable grain shapes can be quite common such as the columnargrains Small gas cavities or shrinkage porosity can also form duringsolidification
Temperature Variations The success or failure of a hot deformationprocess often depends on the ability to control the temperatures withthe workpiece To minimize problems it is desirable to keep theworkpiece temperatures as uniform as possible
Cold Working
Plastic deformation of metals below the recrystallization temperatureis known as cold working The process is usually performed at roomtemperature but mildly elevated temperatures may be used to provideincreased ductility and reduced strength
10715
Department of Industrial amp Production Engineering
Advantages of cold working No heating is required Strength fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved so little if any secondary machining
is required Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized
Disadvantages of cold working Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility
that accompanies strain hardening Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free Imparted directional properties may be detrimental Undesirable residual stresses may be produced
10716
Department of Industrial amp Production Engineering
Warm Working
Deformation produced at temperatures intermediate to hot and coldworking
Compared to cold working it offers the advantages of reduced loads on thetooling and equipment increased material ductility and a possiblereduction in the number of anneals due to a reduction in the amount ofstrain hardening
Compared to hot forming the lower temperatures of warm workingproduce less scaling and decarburization and enable production ofproducts with better dimensional precision and smoother surfaces
The warm regime generally requires less energy than hot working due tothe decreased energy in heating the workpiece energy saved throughhigher precision and the possible elimination of post forming heattreatments
Tools last longer for while they must exert 25 to 60 higher forces thereis less thermal shock and thermal fatigue
10717
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Introduction
Large group of manufacturing processes in which plastic deformation isused to change the shape of metal workpieces
The tool usually called a die applies stresses that exceed the yieldstrength of the metal
The metal takes a shape determined by the geometry of the die
Forming processes tend to be complex systems consisting
Independent Variables
Dependent Variables and
Independent-dependent Interrelations
1076
Department of Industrial amp Production Engineering
Independent Variables Independent variables are those aspects of theprocess over which the engineer has direct control and they are generallyselected or specified when setting up the process Consider some of theindependent variables in a typical forming process
Starting material The engineer is often free to specify the chemistryand condition These may also be chosen for ease in fabrication or theymay be restricted by the final properties desired for the product
Starting geometry of the workpiece This may be dictated by previousprocessing or it may be selected by the engineer from a variety ofavailable shapes Economics often influence this decision
Tool or die geometry This are has many aspects such as the diameterof a rolling mill roll the die angle in wire drawing and the cavitydetails when forging Since tooling will produce and control the metalflow success or failure of a process often depends on tool geometry
1077
Department of Industrial amp Production Engineering
Lubrication Since lubricants also acts as coolants thermal barrierscorrosion inhibitors and parting compounds their selection is anaspect of great importance Specification includes type of lubricantamount to be applied and the method of application
Starting temperature Many material properties vary greatly withtemperature so its selection and control may well dictate the successor failure of an operation
Speed of operation Since speed can directly influence the lubricanteffectiveness the forces required for deformation and the timeavailable for heat transfer It is obvious that its selection would besignificant in a forming operation
Amount of deformation While some processes control this variablethrough die design others such as rolling permits its selection at thediscretion of the engineer
1078
Department of Industrial amp Production Engineering
Dependent Variables After the engineer specifies the independentvariables the process then determine the nature and values for a second setof variables Known as dependent variables these in essence are theconsequences of the dependent variable selection Consider some of thedependent variables in a typical forming process
Force or power requirements Engineers cannot directly specify theforce or power they can only specify the independent variables andthen experience the consequences of the selection The ability topredict the forces or powers however is extremely important for onlyby having this knowledge will the engineer be able to specify or selectthe equipment for the process
Material properties of the product The customer is not interested inthe starting properties but is concerned with our ability to produce thedesired final shape with the desired final properties
1079
Department of Industrial amp Production Engineering
Exit (or Final) temperature Engineering properties can be altered byboth the mechanical and thermal history of the material thus it isimportant to know and control the temperature of the materialthroughout the process
Surface finish and precision Both are characteristics of the resultantproduct that are dependent on the specific details of the process
Nature of the material flow Since properties depend on deformationhistory control here is vital the customer is satisfied only if the desiredgeometric shape is produced with the right set of companion propertiesand without surface or internal defects
10710
Department of Industrial amp Production Engineering
Independent-Dependent Interrelations The following Figure illustrate a majorproblem facing the metal-forming engineer On one side are the independentvariables those aspect of the process for which control is direct and immediate Onthe other are the dependent variables those aspects for which control is totallyindirect It is the dependent variables that we want to control but the dependentvariables are determioned by the process as consequences of the independentvariable selection If we want to change a dependent variable we must determinewhich independent variable is to be changed in what manner and by how much Thusit is important for us to develop a knowledge of the independent variable-dependentvariable interrelations
details flow Material
precision lDimensiona
finish Surface
ratureExit tempe
propertiesProduct
trequiremenPower Forceor
Modeling
Experiment
Experience
ndeformatio ofAmount
ndeformatio of Speed
re temperatuStarting
nLubricatio
geometry Tool
geometry Starting
material Starting
variablesDependent variablest Independen
Schematic of the metal-forming systemshowing independent variablesdependent variables and the variousmeans of relating the two
10711
Department of Industrial amp Production Engineering
The ability to predict and control dependent variables can be obtained inthree distinct ways
Experience This requires long time exposure to the process and isgenerally limited to the specific materials equipment and productsencountered in the realm of past contact
Experiment While possibly the least likely in error direct experimentis both time consuming and costly
Process modeling Here one approaches the problem with a high speedcomputer and one or more mathematical models of the processnumerical values are provided for the various independent variablesand the models are used to compute predictions for the dependentvariables Most techniques rely on the applied theory of plasticity withvarious simplifying assumptions
10712
Department of Industrial amp Production Engineering
General Parameters
While much metal-forming knowledge is specific to a given process there arecertain features that are common to all processes and these will be presentedhere
Friction and Lubrication An important consideration in metaldeformation processes is the friction developed between the tool and theworkpiece For some processes more than 50 of the input energy isspent in overcoming friction The surface finish and dimensional precisionof the product are often directly related to friction Changes in lubricationcan alter the mode of material flow during forming and in so doing createor eliminate defects or modify the properties of the final productProduction rate tool design tool wear and process optimization alldepend on the ability to determine and control process friction
Temperature Concerns In general an increase in temperature brings outa decrease in strength an increase in ductility and a decrease in the rateof strain hardening - all effects that would tend to promote ease ofdeformation
10713
Department of Industrial amp Production Engineering
Forming processes tend to be classified as hot working cold working or warmworking based on both the temperature and the material being formed
Hot Working
Elevated temperatures bring about a decrease in the yield strength of ametal and an increase in ductility At the temperatures of hot workingrecrystallization eliminates the effects of strain hardening so there isno significant increase in yield strength or hardness or correspondingdecrease in ductility
The plastic deformation of metals above their recrystallizationtemperature it is important to note however that the recrystallizationtemperature varies greatly with different materials
In addition the elevated temperatures promote diffusion that canremove or reduce chemical inhomogeneities pores can be welded shutor reduced in size during the deformation and the metallurgicalstructure can often be altered through recrystallization to improve thefinal properties
10714
Department of Industrial amp Production Engineering
Structure and Property Modification by Hot Working When metalssolidify particularly in the large sections that are typical cast strandscoarse structures tend to form with a certain amount of chemicalsegregation The size of the grains is usually not uniform andundesirable grain shapes can be quite common such as the columnargrains Small gas cavities or shrinkage porosity can also form duringsolidification
Temperature Variations The success or failure of a hot deformationprocess often depends on the ability to control the temperatures withthe workpiece To minimize problems it is desirable to keep theworkpiece temperatures as uniform as possible
Cold Working
Plastic deformation of metals below the recrystallization temperatureis known as cold working The process is usually performed at roomtemperature but mildly elevated temperatures may be used to provideincreased ductility and reduced strength
10715
Department of Industrial amp Production Engineering
Advantages of cold working No heating is required Strength fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved so little if any secondary machining
is required Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized
Disadvantages of cold working Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility
that accompanies strain hardening Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free Imparted directional properties may be detrimental Undesirable residual stresses may be produced
10716
Department of Industrial amp Production Engineering
Warm Working
Deformation produced at temperatures intermediate to hot and coldworking
Compared to cold working it offers the advantages of reduced loads on thetooling and equipment increased material ductility and a possiblereduction in the number of anneals due to a reduction in the amount ofstrain hardening
Compared to hot forming the lower temperatures of warm workingproduce less scaling and decarburization and enable production ofproducts with better dimensional precision and smoother surfaces
The warm regime generally requires less energy than hot working due tothe decreased energy in heating the workpiece energy saved throughhigher precision and the possible elimination of post forming heattreatments
Tools last longer for while they must exert 25 to 60 higher forces thereis less thermal shock and thermal fatigue
10717
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Independent Variables Independent variables are those aspects of theprocess over which the engineer has direct control and they are generallyselected or specified when setting up the process Consider some of theindependent variables in a typical forming process
Starting material The engineer is often free to specify the chemistryand condition These may also be chosen for ease in fabrication or theymay be restricted by the final properties desired for the product
Starting geometry of the workpiece This may be dictated by previousprocessing or it may be selected by the engineer from a variety ofavailable shapes Economics often influence this decision
Tool or die geometry This are has many aspects such as the diameterof a rolling mill roll the die angle in wire drawing and the cavitydetails when forging Since tooling will produce and control the metalflow success or failure of a process often depends on tool geometry
1077
Department of Industrial amp Production Engineering
Lubrication Since lubricants also acts as coolants thermal barrierscorrosion inhibitors and parting compounds their selection is anaspect of great importance Specification includes type of lubricantamount to be applied and the method of application
Starting temperature Many material properties vary greatly withtemperature so its selection and control may well dictate the successor failure of an operation
Speed of operation Since speed can directly influence the lubricanteffectiveness the forces required for deformation and the timeavailable for heat transfer It is obvious that its selection would besignificant in a forming operation
Amount of deformation While some processes control this variablethrough die design others such as rolling permits its selection at thediscretion of the engineer
1078
Department of Industrial amp Production Engineering
Dependent Variables After the engineer specifies the independentvariables the process then determine the nature and values for a second setof variables Known as dependent variables these in essence are theconsequences of the dependent variable selection Consider some of thedependent variables in a typical forming process
Force or power requirements Engineers cannot directly specify theforce or power they can only specify the independent variables andthen experience the consequences of the selection The ability topredict the forces or powers however is extremely important for onlyby having this knowledge will the engineer be able to specify or selectthe equipment for the process
Material properties of the product The customer is not interested inthe starting properties but is concerned with our ability to produce thedesired final shape with the desired final properties
1079
Department of Industrial amp Production Engineering
Exit (or Final) temperature Engineering properties can be altered byboth the mechanical and thermal history of the material thus it isimportant to know and control the temperature of the materialthroughout the process
Surface finish and precision Both are characteristics of the resultantproduct that are dependent on the specific details of the process
Nature of the material flow Since properties depend on deformationhistory control here is vital the customer is satisfied only if the desiredgeometric shape is produced with the right set of companion propertiesand without surface or internal defects
10710
Department of Industrial amp Production Engineering
Independent-Dependent Interrelations The following Figure illustrate a majorproblem facing the metal-forming engineer On one side are the independentvariables those aspect of the process for which control is direct and immediate Onthe other are the dependent variables those aspects for which control is totallyindirect It is the dependent variables that we want to control but the dependentvariables are determioned by the process as consequences of the independentvariable selection If we want to change a dependent variable we must determinewhich independent variable is to be changed in what manner and by how much Thusit is important for us to develop a knowledge of the independent variable-dependentvariable interrelations
details flow Material
precision lDimensiona
finish Surface
ratureExit tempe
propertiesProduct
trequiremenPower Forceor
Modeling
Experiment
Experience
ndeformatio ofAmount
ndeformatio of Speed
re temperatuStarting
nLubricatio
geometry Tool
geometry Starting
material Starting
variablesDependent variablest Independen
Schematic of the metal-forming systemshowing independent variablesdependent variables and the variousmeans of relating the two
10711
Department of Industrial amp Production Engineering
The ability to predict and control dependent variables can be obtained inthree distinct ways
Experience This requires long time exposure to the process and isgenerally limited to the specific materials equipment and productsencountered in the realm of past contact
Experiment While possibly the least likely in error direct experimentis both time consuming and costly
Process modeling Here one approaches the problem with a high speedcomputer and one or more mathematical models of the processnumerical values are provided for the various independent variablesand the models are used to compute predictions for the dependentvariables Most techniques rely on the applied theory of plasticity withvarious simplifying assumptions
10712
Department of Industrial amp Production Engineering
General Parameters
While much metal-forming knowledge is specific to a given process there arecertain features that are common to all processes and these will be presentedhere
Friction and Lubrication An important consideration in metaldeformation processes is the friction developed between the tool and theworkpiece For some processes more than 50 of the input energy isspent in overcoming friction The surface finish and dimensional precisionof the product are often directly related to friction Changes in lubricationcan alter the mode of material flow during forming and in so doing createor eliminate defects or modify the properties of the final productProduction rate tool design tool wear and process optimization alldepend on the ability to determine and control process friction
Temperature Concerns In general an increase in temperature brings outa decrease in strength an increase in ductility and a decrease in the rateof strain hardening - all effects that would tend to promote ease ofdeformation
10713
Department of Industrial amp Production Engineering
Forming processes tend to be classified as hot working cold working or warmworking based on both the temperature and the material being formed
Hot Working
Elevated temperatures bring about a decrease in the yield strength of ametal and an increase in ductility At the temperatures of hot workingrecrystallization eliminates the effects of strain hardening so there isno significant increase in yield strength or hardness or correspondingdecrease in ductility
The plastic deformation of metals above their recrystallizationtemperature it is important to note however that the recrystallizationtemperature varies greatly with different materials
In addition the elevated temperatures promote diffusion that canremove or reduce chemical inhomogeneities pores can be welded shutor reduced in size during the deformation and the metallurgicalstructure can often be altered through recrystallization to improve thefinal properties
10714
Department of Industrial amp Production Engineering
Structure and Property Modification by Hot Working When metalssolidify particularly in the large sections that are typical cast strandscoarse structures tend to form with a certain amount of chemicalsegregation The size of the grains is usually not uniform andundesirable grain shapes can be quite common such as the columnargrains Small gas cavities or shrinkage porosity can also form duringsolidification
Temperature Variations The success or failure of a hot deformationprocess often depends on the ability to control the temperatures withthe workpiece To minimize problems it is desirable to keep theworkpiece temperatures as uniform as possible
Cold Working
Plastic deformation of metals below the recrystallization temperatureis known as cold working The process is usually performed at roomtemperature but mildly elevated temperatures may be used to provideincreased ductility and reduced strength
10715
Department of Industrial amp Production Engineering
Advantages of cold working No heating is required Strength fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved so little if any secondary machining
is required Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized
Disadvantages of cold working Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility
that accompanies strain hardening Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free Imparted directional properties may be detrimental Undesirable residual stresses may be produced
10716
Department of Industrial amp Production Engineering
Warm Working
Deformation produced at temperatures intermediate to hot and coldworking
Compared to cold working it offers the advantages of reduced loads on thetooling and equipment increased material ductility and a possiblereduction in the number of anneals due to a reduction in the amount ofstrain hardening
Compared to hot forming the lower temperatures of warm workingproduce less scaling and decarburization and enable production ofproducts with better dimensional precision and smoother surfaces
The warm regime generally requires less energy than hot working due tothe decreased energy in heating the workpiece energy saved throughhigher precision and the possible elimination of post forming heattreatments
Tools last longer for while they must exert 25 to 60 higher forces thereis less thermal shock and thermal fatigue
10717
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Lubrication Since lubricants also acts as coolants thermal barrierscorrosion inhibitors and parting compounds their selection is anaspect of great importance Specification includes type of lubricantamount to be applied and the method of application
Starting temperature Many material properties vary greatly withtemperature so its selection and control may well dictate the successor failure of an operation
Speed of operation Since speed can directly influence the lubricanteffectiveness the forces required for deformation and the timeavailable for heat transfer It is obvious that its selection would besignificant in a forming operation
Amount of deformation While some processes control this variablethrough die design others such as rolling permits its selection at thediscretion of the engineer
1078
Department of Industrial amp Production Engineering
Dependent Variables After the engineer specifies the independentvariables the process then determine the nature and values for a second setof variables Known as dependent variables these in essence are theconsequences of the dependent variable selection Consider some of thedependent variables in a typical forming process
Force or power requirements Engineers cannot directly specify theforce or power they can only specify the independent variables andthen experience the consequences of the selection The ability topredict the forces or powers however is extremely important for onlyby having this knowledge will the engineer be able to specify or selectthe equipment for the process
Material properties of the product The customer is not interested inthe starting properties but is concerned with our ability to produce thedesired final shape with the desired final properties
1079
Department of Industrial amp Production Engineering
Exit (or Final) temperature Engineering properties can be altered byboth the mechanical and thermal history of the material thus it isimportant to know and control the temperature of the materialthroughout the process
Surface finish and precision Both are characteristics of the resultantproduct that are dependent on the specific details of the process
Nature of the material flow Since properties depend on deformationhistory control here is vital the customer is satisfied only if the desiredgeometric shape is produced with the right set of companion propertiesand without surface or internal defects
10710
Department of Industrial amp Production Engineering
Independent-Dependent Interrelations The following Figure illustrate a majorproblem facing the metal-forming engineer On one side are the independentvariables those aspect of the process for which control is direct and immediate Onthe other are the dependent variables those aspects for which control is totallyindirect It is the dependent variables that we want to control but the dependentvariables are determioned by the process as consequences of the independentvariable selection If we want to change a dependent variable we must determinewhich independent variable is to be changed in what manner and by how much Thusit is important for us to develop a knowledge of the independent variable-dependentvariable interrelations
details flow Material
precision lDimensiona
finish Surface
ratureExit tempe
propertiesProduct
trequiremenPower Forceor
Modeling
Experiment
Experience
ndeformatio ofAmount
ndeformatio of Speed
re temperatuStarting
nLubricatio
geometry Tool
geometry Starting
material Starting
variablesDependent variablest Independen
Schematic of the metal-forming systemshowing independent variablesdependent variables and the variousmeans of relating the two
10711
Department of Industrial amp Production Engineering
The ability to predict and control dependent variables can be obtained inthree distinct ways
Experience This requires long time exposure to the process and isgenerally limited to the specific materials equipment and productsencountered in the realm of past contact
Experiment While possibly the least likely in error direct experimentis both time consuming and costly
Process modeling Here one approaches the problem with a high speedcomputer and one or more mathematical models of the processnumerical values are provided for the various independent variablesand the models are used to compute predictions for the dependentvariables Most techniques rely on the applied theory of plasticity withvarious simplifying assumptions
10712
Department of Industrial amp Production Engineering
General Parameters
While much metal-forming knowledge is specific to a given process there arecertain features that are common to all processes and these will be presentedhere
Friction and Lubrication An important consideration in metaldeformation processes is the friction developed between the tool and theworkpiece For some processes more than 50 of the input energy isspent in overcoming friction The surface finish and dimensional precisionof the product are often directly related to friction Changes in lubricationcan alter the mode of material flow during forming and in so doing createor eliminate defects or modify the properties of the final productProduction rate tool design tool wear and process optimization alldepend on the ability to determine and control process friction
Temperature Concerns In general an increase in temperature brings outa decrease in strength an increase in ductility and a decrease in the rateof strain hardening - all effects that would tend to promote ease ofdeformation
10713
Department of Industrial amp Production Engineering
Forming processes tend to be classified as hot working cold working or warmworking based on both the temperature and the material being formed
Hot Working
Elevated temperatures bring about a decrease in the yield strength of ametal and an increase in ductility At the temperatures of hot workingrecrystallization eliminates the effects of strain hardening so there isno significant increase in yield strength or hardness or correspondingdecrease in ductility
The plastic deformation of metals above their recrystallizationtemperature it is important to note however that the recrystallizationtemperature varies greatly with different materials
In addition the elevated temperatures promote diffusion that canremove or reduce chemical inhomogeneities pores can be welded shutor reduced in size during the deformation and the metallurgicalstructure can often be altered through recrystallization to improve thefinal properties
10714
Department of Industrial amp Production Engineering
Structure and Property Modification by Hot Working When metalssolidify particularly in the large sections that are typical cast strandscoarse structures tend to form with a certain amount of chemicalsegregation The size of the grains is usually not uniform andundesirable grain shapes can be quite common such as the columnargrains Small gas cavities or shrinkage porosity can also form duringsolidification
Temperature Variations The success or failure of a hot deformationprocess often depends on the ability to control the temperatures withthe workpiece To minimize problems it is desirable to keep theworkpiece temperatures as uniform as possible
Cold Working
Plastic deformation of metals below the recrystallization temperatureis known as cold working The process is usually performed at roomtemperature but mildly elevated temperatures may be used to provideincreased ductility and reduced strength
10715
Department of Industrial amp Production Engineering
Advantages of cold working No heating is required Strength fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved so little if any secondary machining
is required Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized
Disadvantages of cold working Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility
that accompanies strain hardening Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free Imparted directional properties may be detrimental Undesirable residual stresses may be produced
10716
Department of Industrial amp Production Engineering
Warm Working
Deformation produced at temperatures intermediate to hot and coldworking
Compared to cold working it offers the advantages of reduced loads on thetooling and equipment increased material ductility and a possiblereduction in the number of anneals due to a reduction in the amount ofstrain hardening
Compared to hot forming the lower temperatures of warm workingproduce less scaling and decarburization and enable production ofproducts with better dimensional precision and smoother surfaces
The warm regime generally requires less energy than hot working due tothe decreased energy in heating the workpiece energy saved throughhigher precision and the possible elimination of post forming heattreatments
Tools last longer for while they must exert 25 to 60 higher forces thereis less thermal shock and thermal fatigue
10717
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Dependent Variables After the engineer specifies the independentvariables the process then determine the nature and values for a second setof variables Known as dependent variables these in essence are theconsequences of the dependent variable selection Consider some of thedependent variables in a typical forming process
Force or power requirements Engineers cannot directly specify theforce or power they can only specify the independent variables andthen experience the consequences of the selection The ability topredict the forces or powers however is extremely important for onlyby having this knowledge will the engineer be able to specify or selectthe equipment for the process
Material properties of the product The customer is not interested inthe starting properties but is concerned with our ability to produce thedesired final shape with the desired final properties
1079
Department of Industrial amp Production Engineering
Exit (or Final) temperature Engineering properties can be altered byboth the mechanical and thermal history of the material thus it isimportant to know and control the temperature of the materialthroughout the process
Surface finish and precision Both are characteristics of the resultantproduct that are dependent on the specific details of the process
Nature of the material flow Since properties depend on deformationhistory control here is vital the customer is satisfied only if the desiredgeometric shape is produced with the right set of companion propertiesand without surface or internal defects
10710
Department of Industrial amp Production Engineering
Independent-Dependent Interrelations The following Figure illustrate a majorproblem facing the metal-forming engineer On one side are the independentvariables those aspect of the process for which control is direct and immediate Onthe other are the dependent variables those aspects for which control is totallyindirect It is the dependent variables that we want to control but the dependentvariables are determioned by the process as consequences of the independentvariable selection If we want to change a dependent variable we must determinewhich independent variable is to be changed in what manner and by how much Thusit is important for us to develop a knowledge of the independent variable-dependentvariable interrelations
details flow Material
precision lDimensiona
finish Surface
ratureExit tempe
propertiesProduct
trequiremenPower Forceor
Modeling
Experiment
Experience
ndeformatio ofAmount
ndeformatio of Speed
re temperatuStarting
nLubricatio
geometry Tool
geometry Starting
material Starting
variablesDependent variablest Independen
Schematic of the metal-forming systemshowing independent variablesdependent variables and the variousmeans of relating the two
10711
Department of Industrial amp Production Engineering
The ability to predict and control dependent variables can be obtained inthree distinct ways
Experience This requires long time exposure to the process and isgenerally limited to the specific materials equipment and productsencountered in the realm of past contact
Experiment While possibly the least likely in error direct experimentis both time consuming and costly
Process modeling Here one approaches the problem with a high speedcomputer and one or more mathematical models of the processnumerical values are provided for the various independent variablesand the models are used to compute predictions for the dependentvariables Most techniques rely on the applied theory of plasticity withvarious simplifying assumptions
10712
Department of Industrial amp Production Engineering
General Parameters
While much metal-forming knowledge is specific to a given process there arecertain features that are common to all processes and these will be presentedhere
Friction and Lubrication An important consideration in metaldeformation processes is the friction developed between the tool and theworkpiece For some processes more than 50 of the input energy isspent in overcoming friction The surface finish and dimensional precisionof the product are often directly related to friction Changes in lubricationcan alter the mode of material flow during forming and in so doing createor eliminate defects or modify the properties of the final productProduction rate tool design tool wear and process optimization alldepend on the ability to determine and control process friction
Temperature Concerns In general an increase in temperature brings outa decrease in strength an increase in ductility and a decrease in the rateof strain hardening - all effects that would tend to promote ease ofdeformation
10713
Department of Industrial amp Production Engineering
Forming processes tend to be classified as hot working cold working or warmworking based on both the temperature and the material being formed
Hot Working
Elevated temperatures bring about a decrease in the yield strength of ametal and an increase in ductility At the temperatures of hot workingrecrystallization eliminates the effects of strain hardening so there isno significant increase in yield strength or hardness or correspondingdecrease in ductility
The plastic deformation of metals above their recrystallizationtemperature it is important to note however that the recrystallizationtemperature varies greatly with different materials
In addition the elevated temperatures promote diffusion that canremove or reduce chemical inhomogeneities pores can be welded shutor reduced in size during the deformation and the metallurgicalstructure can often be altered through recrystallization to improve thefinal properties
10714
Department of Industrial amp Production Engineering
Structure and Property Modification by Hot Working When metalssolidify particularly in the large sections that are typical cast strandscoarse structures tend to form with a certain amount of chemicalsegregation The size of the grains is usually not uniform andundesirable grain shapes can be quite common such as the columnargrains Small gas cavities or shrinkage porosity can also form duringsolidification
Temperature Variations The success or failure of a hot deformationprocess often depends on the ability to control the temperatures withthe workpiece To minimize problems it is desirable to keep theworkpiece temperatures as uniform as possible
Cold Working
Plastic deformation of metals below the recrystallization temperatureis known as cold working The process is usually performed at roomtemperature but mildly elevated temperatures may be used to provideincreased ductility and reduced strength
10715
Department of Industrial amp Production Engineering
Advantages of cold working No heating is required Strength fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved so little if any secondary machining
is required Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized
Disadvantages of cold working Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility
that accompanies strain hardening Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free Imparted directional properties may be detrimental Undesirable residual stresses may be produced
10716
Department of Industrial amp Production Engineering
Warm Working
Deformation produced at temperatures intermediate to hot and coldworking
Compared to cold working it offers the advantages of reduced loads on thetooling and equipment increased material ductility and a possiblereduction in the number of anneals due to a reduction in the amount ofstrain hardening
Compared to hot forming the lower temperatures of warm workingproduce less scaling and decarburization and enable production ofproducts with better dimensional precision and smoother surfaces
The warm regime generally requires less energy than hot working due tothe decreased energy in heating the workpiece energy saved throughhigher precision and the possible elimination of post forming heattreatments
Tools last longer for while they must exert 25 to 60 higher forces thereis less thermal shock and thermal fatigue
10717
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Exit (or Final) temperature Engineering properties can be altered byboth the mechanical and thermal history of the material thus it isimportant to know and control the temperature of the materialthroughout the process
Surface finish and precision Both are characteristics of the resultantproduct that are dependent on the specific details of the process
Nature of the material flow Since properties depend on deformationhistory control here is vital the customer is satisfied only if the desiredgeometric shape is produced with the right set of companion propertiesand without surface or internal defects
10710
Department of Industrial amp Production Engineering
Independent-Dependent Interrelations The following Figure illustrate a majorproblem facing the metal-forming engineer On one side are the independentvariables those aspect of the process for which control is direct and immediate Onthe other are the dependent variables those aspects for which control is totallyindirect It is the dependent variables that we want to control but the dependentvariables are determioned by the process as consequences of the independentvariable selection If we want to change a dependent variable we must determinewhich independent variable is to be changed in what manner and by how much Thusit is important for us to develop a knowledge of the independent variable-dependentvariable interrelations
details flow Material
precision lDimensiona
finish Surface
ratureExit tempe
propertiesProduct
trequiremenPower Forceor
Modeling
Experiment
Experience
ndeformatio ofAmount
ndeformatio of Speed
re temperatuStarting
nLubricatio
geometry Tool
geometry Starting
material Starting
variablesDependent variablest Independen
Schematic of the metal-forming systemshowing independent variablesdependent variables and the variousmeans of relating the two
10711
Department of Industrial amp Production Engineering
The ability to predict and control dependent variables can be obtained inthree distinct ways
Experience This requires long time exposure to the process and isgenerally limited to the specific materials equipment and productsencountered in the realm of past contact
Experiment While possibly the least likely in error direct experimentis both time consuming and costly
Process modeling Here one approaches the problem with a high speedcomputer and one or more mathematical models of the processnumerical values are provided for the various independent variablesand the models are used to compute predictions for the dependentvariables Most techniques rely on the applied theory of plasticity withvarious simplifying assumptions
10712
Department of Industrial amp Production Engineering
General Parameters
While much metal-forming knowledge is specific to a given process there arecertain features that are common to all processes and these will be presentedhere
Friction and Lubrication An important consideration in metaldeformation processes is the friction developed between the tool and theworkpiece For some processes more than 50 of the input energy isspent in overcoming friction The surface finish and dimensional precisionof the product are often directly related to friction Changes in lubricationcan alter the mode of material flow during forming and in so doing createor eliminate defects or modify the properties of the final productProduction rate tool design tool wear and process optimization alldepend on the ability to determine and control process friction
Temperature Concerns In general an increase in temperature brings outa decrease in strength an increase in ductility and a decrease in the rateof strain hardening - all effects that would tend to promote ease ofdeformation
10713
Department of Industrial amp Production Engineering
Forming processes tend to be classified as hot working cold working or warmworking based on both the temperature and the material being formed
Hot Working
Elevated temperatures bring about a decrease in the yield strength of ametal and an increase in ductility At the temperatures of hot workingrecrystallization eliminates the effects of strain hardening so there isno significant increase in yield strength or hardness or correspondingdecrease in ductility
The plastic deformation of metals above their recrystallizationtemperature it is important to note however that the recrystallizationtemperature varies greatly with different materials
In addition the elevated temperatures promote diffusion that canremove or reduce chemical inhomogeneities pores can be welded shutor reduced in size during the deformation and the metallurgicalstructure can often be altered through recrystallization to improve thefinal properties
10714
Department of Industrial amp Production Engineering
Structure and Property Modification by Hot Working When metalssolidify particularly in the large sections that are typical cast strandscoarse structures tend to form with a certain amount of chemicalsegregation The size of the grains is usually not uniform andundesirable grain shapes can be quite common such as the columnargrains Small gas cavities or shrinkage porosity can also form duringsolidification
Temperature Variations The success or failure of a hot deformationprocess often depends on the ability to control the temperatures withthe workpiece To minimize problems it is desirable to keep theworkpiece temperatures as uniform as possible
Cold Working
Plastic deformation of metals below the recrystallization temperatureis known as cold working The process is usually performed at roomtemperature but mildly elevated temperatures may be used to provideincreased ductility and reduced strength
10715
Department of Industrial amp Production Engineering
Advantages of cold working No heating is required Strength fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved so little if any secondary machining
is required Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized
Disadvantages of cold working Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility
that accompanies strain hardening Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free Imparted directional properties may be detrimental Undesirable residual stresses may be produced
10716
Department of Industrial amp Production Engineering
Warm Working
Deformation produced at temperatures intermediate to hot and coldworking
Compared to cold working it offers the advantages of reduced loads on thetooling and equipment increased material ductility and a possiblereduction in the number of anneals due to a reduction in the amount ofstrain hardening
Compared to hot forming the lower temperatures of warm workingproduce less scaling and decarburization and enable production ofproducts with better dimensional precision and smoother surfaces
The warm regime generally requires less energy than hot working due tothe decreased energy in heating the workpiece energy saved throughhigher precision and the possible elimination of post forming heattreatments
Tools last longer for while they must exert 25 to 60 higher forces thereis less thermal shock and thermal fatigue
10717
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Independent-Dependent Interrelations The following Figure illustrate a majorproblem facing the metal-forming engineer On one side are the independentvariables those aspect of the process for which control is direct and immediate Onthe other are the dependent variables those aspects for which control is totallyindirect It is the dependent variables that we want to control but the dependentvariables are determioned by the process as consequences of the independentvariable selection If we want to change a dependent variable we must determinewhich independent variable is to be changed in what manner and by how much Thusit is important for us to develop a knowledge of the independent variable-dependentvariable interrelations
details flow Material
precision lDimensiona
finish Surface
ratureExit tempe
propertiesProduct
trequiremenPower Forceor
Modeling
Experiment
Experience
ndeformatio ofAmount
ndeformatio of Speed
re temperatuStarting
nLubricatio
geometry Tool
geometry Starting
material Starting
variablesDependent variablest Independen
Schematic of the metal-forming systemshowing independent variablesdependent variables and the variousmeans of relating the two
10711
Department of Industrial amp Production Engineering
The ability to predict and control dependent variables can be obtained inthree distinct ways
Experience This requires long time exposure to the process and isgenerally limited to the specific materials equipment and productsencountered in the realm of past contact
Experiment While possibly the least likely in error direct experimentis both time consuming and costly
Process modeling Here one approaches the problem with a high speedcomputer and one or more mathematical models of the processnumerical values are provided for the various independent variablesand the models are used to compute predictions for the dependentvariables Most techniques rely on the applied theory of plasticity withvarious simplifying assumptions
10712
Department of Industrial amp Production Engineering
General Parameters
While much metal-forming knowledge is specific to a given process there arecertain features that are common to all processes and these will be presentedhere
Friction and Lubrication An important consideration in metaldeformation processes is the friction developed between the tool and theworkpiece For some processes more than 50 of the input energy isspent in overcoming friction The surface finish and dimensional precisionof the product are often directly related to friction Changes in lubricationcan alter the mode of material flow during forming and in so doing createor eliminate defects or modify the properties of the final productProduction rate tool design tool wear and process optimization alldepend on the ability to determine and control process friction
Temperature Concerns In general an increase in temperature brings outa decrease in strength an increase in ductility and a decrease in the rateof strain hardening - all effects that would tend to promote ease ofdeformation
10713
Department of Industrial amp Production Engineering
Forming processes tend to be classified as hot working cold working or warmworking based on both the temperature and the material being formed
Hot Working
Elevated temperatures bring about a decrease in the yield strength of ametal and an increase in ductility At the temperatures of hot workingrecrystallization eliminates the effects of strain hardening so there isno significant increase in yield strength or hardness or correspondingdecrease in ductility
The plastic deformation of metals above their recrystallizationtemperature it is important to note however that the recrystallizationtemperature varies greatly with different materials
In addition the elevated temperatures promote diffusion that canremove or reduce chemical inhomogeneities pores can be welded shutor reduced in size during the deformation and the metallurgicalstructure can often be altered through recrystallization to improve thefinal properties
10714
Department of Industrial amp Production Engineering
Structure and Property Modification by Hot Working When metalssolidify particularly in the large sections that are typical cast strandscoarse structures tend to form with a certain amount of chemicalsegregation The size of the grains is usually not uniform andundesirable grain shapes can be quite common such as the columnargrains Small gas cavities or shrinkage porosity can also form duringsolidification
Temperature Variations The success or failure of a hot deformationprocess often depends on the ability to control the temperatures withthe workpiece To minimize problems it is desirable to keep theworkpiece temperatures as uniform as possible
Cold Working
Plastic deformation of metals below the recrystallization temperatureis known as cold working The process is usually performed at roomtemperature but mildly elevated temperatures may be used to provideincreased ductility and reduced strength
10715
Department of Industrial amp Production Engineering
Advantages of cold working No heating is required Strength fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved so little if any secondary machining
is required Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized
Disadvantages of cold working Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility
that accompanies strain hardening Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free Imparted directional properties may be detrimental Undesirable residual stresses may be produced
10716
Department of Industrial amp Production Engineering
Warm Working
Deformation produced at temperatures intermediate to hot and coldworking
Compared to cold working it offers the advantages of reduced loads on thetooling and equipment increased material ductility and a possiblereduction in the number of anneals due to a reduction in the amount ofstrain hardening
Compared to hot forming the lower temperatures of warm workingproduce less scaling and decarburization and enable production ofproducts with better dimensional precision and smoother surfaces
The warm regime generally requires less energy than hot working due tothe decreased energy in heating the workpiece energy saved throughhigher precision and the possible elimination of post forming heattreatments
Tools last longer for while they must exert 25 to 60 higher forces thereis less thermal shock and thermal fatigue
10717
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
The ability to predict and control dependent variables can be obtained inthree distinct ways
Experience This requires long time exposure to the process and isgenerally limited to the specific materials equipment and productsencountered in the realm of past contact
Experiment While possibly the least likely in error direct experimentis both time consuming and costly
Process modeling Here one approaches the problem with a high speedcomputer and one or more mathematical models of the processnumerical values are provided for the various independent variablesand the models are used to compute predictions for the dependentvariables Most techniques rely on the applied theory of plasticity withvarious simplifying assumptions
10712
Department of Industrial amp Production Engineering
General Parameters
While much metal-forming knowledge is specific to a given process there arecertain features that are common to all processes and these will be presentedhere
Friction and Lubrication An important consideration in metaldeformation processes is the friction developed between the tool and theworkpiece For some processes more than 50 of the input energy isspent in overcoming friction The surface finish and dimensional precisionof the product are often directly related to friction Changes in lubricationcan alter the mode of material flow during forming and in so doing createor eliminate defects or modify the properties of the final productProduction rate tool design tool wear and process optimization alldepend on the ability to determine and control process friction
Temperature Concerns In general an increase in temperature brings outa decrease in strength an increase in ductility and a decrease in the rateof strain hardening - all effects that would tend to promote ease ofdeformation
10713
Department of Industrial amp Production Engineering
Forming processes tend to be classified as hot working cold working or warmworking based on both the temperature and the material being formed
Hot Working
Elevated temperatures bring about a decrease in the yield strength of ametal and an increase in ductility At the temperatures of hot workingrecrystallization eliminates the effects of strain hardening so there isno significant increase in yield strength or hardness or correspondingdecrease in ductility
The plastic deformation of metals above their recrystallizationtemperature it is important to note however that the recrystallizationtemperature varies greatly with different materials
In addition the elevated temperatures promote diffusion that canremove or reduce chemical inhomogeneities pores can be welded shutor reduced in size during the deformation and the metallurgicalstructure can often be altered through recrystallization to improve thefinal properties
10714
Department of Industrial amp Production Engineering
Structure and Property Modification by Hot Working When metalssolidify particularly in the large sections that are typical cast strandscoarse structures tend to form with a certain amount of chemicalsegregation The size of the grains is usually not uniform andundesirable grain shapes can be quite common such as the columnargrains Small gas cavities or shrinkage porosity can also form duringsolidification
Temperature Variations The success or failure of a hot deformationprocess often depends on the ability to control the temperatures withthe workpiece To minimize problems it is desirable to keep theworkpiece temperatures as uniform as possible
Cold Working
Plastic deformation of metals below the recrystallization temperatureis known as cold working The process is usually performed at roomtemperature but mildly elevated temperatures may be used to provideincreased ductility and reduced strength
10715
Department of Industrial amp Production Engineering
Advantages of cold working No heating is required Strength fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved so little if any secondary machining
is required Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized
Disadvantages of cold working Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility
that accompanies strain hardening Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free Imparted directional properties may be detrimental Undesirable residual stresses may be produced
10716
Department of Industrial amp Production Engineering
Warm Working
Deformation produced at temperatures intermediate to hot and coldworking
Compared to cold working it offers the advantages of reduced loads on thetooling and equipment increased material ductility and a possiblereduction in the number of anneals due to a reduction in the amount ofstrain hardening
Compared to hot forming the lower temperatures of warm workingproduce less scaling and decarburization and enable production ofproducts with better dimensional precision and smoother surfaces
The warm regime generally requires less energy than hot working due tothe decreased energy in heating the workpiece energy saved throughhigher precision and the possible elimination of post forming heattreatments
Tools last longer for while they must exert 25 to 60 higher forces thereis less thermal shock and thermal fatigue
10717
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
General Parameters
While much metal-forming knowledge is specific to a given process there arecertain features that are common to all processes and these will be presentedhere
Friction and Lubrication An important consideration in metaldeformation processes is the friction developed between the tool and theworkpiece For some processes more than 50 of the input energy isspent in overcoming friction The surface finish and dimensional precisionof the product are often directly related to friction Changes in lubricationcan alter the mode of material flow during forming and in so doing createor eliminate defects or modify the properties of the final productProduction rate tool design tool wear and process optimization alldepend on the ability to determine and control process friction
Temperature Concerns In general an increase in temperature brings outa decrease in strength an increase in ductility and a decrease in the rateof strain hardening - all effects that would tend to promote ease ofdeformation
10713
Department of Industrial amp Production Engineering
Forming processes tend to be classified as hot working cold working or warmworking based on both the temperature and the material being formed
Hot Working
Elevated temperatures bring about a decrease in the yield strength of ametal and an increase in ductility At the temperatures of hot workingrecrystallization eliminates the effects of strain hardening so there isno significant increase in yield strength or hardness or correspondingdecrease in ductility
The plastic deformation of metals above their recrystallizationtemperature it is important to note however that the recrystallizationtemperature varies greatly with different materials
In addition the elevated temperatures promote diffusion that canremove or reduce chemical inhomogeneities pores can be welded shutor reduced in size during the deformation and the metallurgicalstructure can often be altered through recrystallization to improve thefinal properties
10714
Department of Industrial amp Production Engineering
Structure and Property Modification by Hot Working When metalssolidify particularly in the large sections that are typical cast strandscoarse structures tend to form with a certain amount of chemicalsegregation The size of the grains is usually not uniform andundesirable grain shapes can be quite common such as the columnargrains Small gas cavities or shrinkage porosity can also form duringsolidification
Temperature Variations The success or failure of a hot deformationprocess often depends on the ability to control the temperatures withthe workpiece To minimize problems it is desirable to keep theworkpiece temperatures as uniform as possible
Cold Working
Plastic deformation of metals below the recrystallization temperatureis known as cold working The process is usually performed at roomtemperature but mildly elevated temperatures may be used to provideincreased ductility and reduced strength
10715
Department of Industrial amp Production Engineering
Advantages of cold working No heating is required Strength fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved so little if any secondary machining
is required Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized
Disadvantages of cold working Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility
that accompanies strain hardening Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free Imparted directional properties may be detrimental Undesirable residual stresses may be produced
10716
Department of Industrial amp Production Engineering
Warm Working
Deformation produced at temperatures intermediate to hot and coldworking
Compared to cold working it offers the advantages of reduced loads on thetooling and equipment increased material ductility and a possiblereduction in the number of anneals due to a reduction in the amount ofstrain hardening
Compared to hot forming the lower temperatures of warm workingproduce less scaling and decarburization and enable production ofproducts with better dimensional precision and smoother surfaces
The warm regime generally requires less energy than hot working due tothe decreased energy in heating the workpiece energy saved throughhigher precision and the possible elimination of post forming heattreatments
Tools last longer for while they must exert 25 to 60 higher forces thereis less thermal shock and thermal fatigue
10717
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Forming processes tend to be classified as hot working cold working or warmworking based on both the temperature and the material being formed
Hot Working
Elevated temperatures bring about a decrease in the yield strength of ametal and an increase in ductility At the temperatures of hot workingrecrystallization eliminates the effects of strain hardening so there isno significant increase in yield strength or hardness or correspondingdecrease in ductility
The plastic deformation of metals above their recrystallizationtemperature it is important to note however that the recrystallizationtemperature varies greatly with different materials
In addition the elevated temperatures promote diffusion that canremove or reduce chemical inhomogeneities pores can be welded shutor reduced in size during the deformation and the metallurgicalstructure can often be altered through recrystallization to improve thefinal properties
10714
Department of Industrial amp Production Engineering
Structure and Property Modification by Hot Working When metalssolidify particularly in the large sections that are typical cast strandscoarse structures tend to form with a certain amount of chemicalsegregation The size of the grains is usually not uniform andundesirable grain shapes can be quite common such as the columnargrains Small gas cavities or shrinkage porosity can also form duringsolidification
Temperature Variations The success or failure of a hot deformationprocess often depends on the ability to control the temperatures withthe workpiece To minimize problems it is desirable to keep theworkpiece temperatures as uniform as possible
Cold Working
Plastic deformation of metals below the recrystallization temperatureis known as cold working The process is usually performed at roomtemperature but mildly elevated temperatures may be used to provideincreased ductility and reduced strength
10715
Department of Industrial amp Production Engineering
Advantages of cold working No heating is required Strength fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved so little if any secondary machining
is required Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized
Disadvantages of cold working Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility
that accompanies strain hardening Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free Imparted directional properties may be detrimental Undesirable residual stresses may be produced
10716
Department of Industrial amp Production Engineering
Warm Working
Deformation produced at temperatures intermediate to hot and coldworking
Compared to cold working it offers the advantages of reduced loads on thetooling and equipment increased material ductility and a possiblereduction in the number of anneals due to a reduction in the amount ofstrain hardening
Compared to hot forming the lower temperatures of warm workingproduce less scaling and decarburization and enable production ofproducts with better dimensional precision and smoother surfaces
The warm regime generally requires less energy than hot working due tothe decreased energy in heating the workpiece energy saved throughhigher precision and the possible elimination of post forming heattreatments
Tools last longer for while they must exert 25 to 60 higher forces thereis less thermal shock and thermal fatigue
10717
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Structure and Property Modification by Hot Working When metalssolidify particularly in the large sections that are typical cast strandscoarse structures tend to form with a certain amount of chemicalsegregation The size of the grains is usually not uniform andundesirable grain shapes can be quite common such as the columnargrains Small gas cavities or shrinkage porosity can also form duringsolidification
Temperature Variations The success or failure of a hot deformationprocess often depends on the ability to control the temperatures withthe workpiece To minimize problems it is desirable to keep theworkpiece temperatures as uniform as possible
Cold Working
Plastic deformation of metals below the recrystallization temperatureis known as cold working The process is usually performed at roomtemperature but mildly elevated temperatures may be used to provideincreased ductility and reduced strength
10715
Department of Industrial amp Production Engineering
Advantages of cold working No heating is required Strength fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved so little if any secondary machining
is required Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized
Disadvantages of cold working Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility
that accompanies strain hardening Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free Imparted directional properties may be detrimental Undesirable residual stresses may be produced
10716
Department of Industrial amp Production Engineering
Warm Working
Deformation produced at temperatures intermediate to hot and coldworking
Compared to cold working it offers the advantages of reduced loads on thetooling and equipment increased material ductility and a possiblereduction in the number of anneals due to a reduction in the amount ofstrain hardening
Compared to hot forming the lower temperatures of warm workingproduce less scaling and decarburization and enable production ofproducts with better dimensional precision and smoother surfaces
The warm regime generally requires less energy than hot working due tothe decreased energy in heating the workpiece energy saved throughhigher precision and the possible elimination of post forming heattreatments
Tools last longer for while they must exert 25 to 60 higher forces thereis less thermal shock and thermal fatigue
10717
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Advantages of cold working No heating is required Strength fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved so little if any secondary machining
is required Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized
Disadvantages of cold working Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility
that accompanies strain hardening Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free Imparted directional properties may be detrimental Undesirable residual stresses may be produced
10716
Department of Industrial amp Production Engineering
Warm Working
Deformation produced at temperatures intermediate to hot and coldworking
Compared to cold working it offers the advantages of reduced loads on thetooling and equipment increased material ductility and a possiblereduction in the number of anneals due to a reduction in the amount ofstrain hardening
Compared to hot forming the lower temperatures of warm workingproduce less scaling and decarburization and enable production ofproducts with better dimensional precision and smoother surfaces
The warm regime generally requires less energy than hot working due tothe decreased energy in heating the workpiece energy saved throughhigher precision and the possible elimination of post forming heattreatments
Tools last longer for while they must exert 25 to 60 higher forces thereis less thermal shock and thermal fatigue
10717
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Warm Working
Deformation produced at temperatures intermediate to hot and coldworking
Compared to cold working it offers the advantages of reduced loads on thetooling and equipment increased material ductility and a possiblereduction in the number of anneals due to a reduction in the amount ofstrain hardening
Compared to hot forming the lower temperatures of warm workingproduce less scaling and decarburization and enable production ofproducts with better dimensional precision and smoother surfaces
The warm regime generally requires less energy than hot working due tothe decreased energy in heating the workpiece energy saved throughhigher precision and the possible elimination of post forming heattreatments
Tools last longer for while they must exert 25 to 60 higher forces thereis less thermal shock and thermal fatigue
10717
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Stresses in Metal FormingStresses to plastically deform the metal are usually compressive Examples rolling forging extrusion
However some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses
Material Properties in Metal FormingDesirable material properties Low yield strength High ductility
These properties are affected by temperature Ductility increases and yield strength decreases when work
temperature is raisedOther factors Strain rate and friction
10718
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Basic Types of Deformation Processes
Bulk deformation Processes
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Cutting or Shearing
Bending
Deep drawing
Miscellaneous processes
10719
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
ForgingRolling
Extrusion Drawing
Bending DrawingShearing
Bulk deformation Processes
Sheet Metalworking
10720
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
LECTURE-02 BULK DEFORMATION
PROCESSES - ROLLING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Rolling
Rolling is the most widely used deformation process It consists of passingmetal between two rollers which exert compressive stresses reducing themetal thickness Where simple shapes are to be made in large quantityrolling is the most economical process Rolled products include sheetsstructural shapes and rails as well as intermediate shapes for wire drawing orforging Circular shapes lsquoIrsquo beams and railway tracks are manufactured usinggrooved rolls
10722
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Practically all metals which are not used in cast form are reduced to somestandard shapes for subsequent processing
Manufacturing companies producing metals in form of ingots which areobtained by casting liquid metal into a square cross section
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast the liquidmetal into slabs billets or blooms
These shapes are further processed through hot rolling forging orextrusion to produce materials in standard form such as plates sheetsrods tubes and structural sections
10723
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Sequence of operations
Schematic layout ofvarious flat and shaperolling processes
10724
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Basic Principles of Rolling
When a piece of metal is rolled in between two rolls the thickness is reducedas a result of the compressive stresses exerted by the rolls and it can be treatedas a two-dimensional deformation in the thickness and length directionsneglecting the width direction This is due to the fact that the length of contactbetween the rolls and workpiece is generally much smaller than the width ofthe sheet passing through and the undeformed material on both sides of theroll gap is restraining the lateral expansion along the width direction
The metal piece experiences both vertical and horizontal stresses caused by thecompressive load from the rolls and the restrains by the portions of the metalpiece before and after the material in contact with the roll respectively
As the rolls exert a vertical stress on the metal piece the metal piece exerts thesame amount of stress back onto the rolls itself As such the rolls are subjectedto elastic deformation due to this stress induced by the workpiece As shown inthe figure below the rolls in a 4-high rolling mill are subjected to four kinds ofdeformation
10725
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Deflection of the back-up rolls Deflection of the work rolls Flattening of the work rolls caused by contact with the back-up rolls
and workpiece Flattening of the back-up rolls caused by contact with the work rolls
10726
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Rolling is the process of reducing the thickess or changing the cross-section of a long workpiece by compressive forces applied through a setof rolls The rolling processes can be done by
Flat Rolling
Shape Rolling
Production of Seamless Tubing amp Pipe
Flat Rolling
Metal strip enters the roll gap
The strip is reduced in size by the metal rolls
The velocity of the strip is increased the metal strip is reduced in size
Factors affecting Rolling Process
Frictional Forces
Roll Force and Power Requirement
10727
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering 10728
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Flat-Rolling Practice
Hot rolling The initial break down of an ingot Continuously cast slab Structure may be brittle Converts the cast structure to a wrought structure
Finer grainsEnhanced ductility
Reduction in defectsContinuous Casting Is replacing traditional methods Faster amp better
Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed father by shape rolling
I-beamsRailroad rails
10729
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Billets ndash smaller than blooms and rolled into bars and rods
Cold rolling
carried out at room temperature
Produces sheet and strip metal
Better surface finish ndash less scale
Pack rolling ndash when two or more layers of metal are rolled together
Changes in grain structure during hot-rolling
10730
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Rolling Defects in Sheets and Plates
The elastic deflection of the work rolls results in an uneven widthwisedistribution of the workpiece thickness in such a way where the thicknessis greater at the center of the width and smaller at the edges In order tosolve the bending of the work rolls several methods can be adopted
Smaller work rolls are more prone to greater bending under high roll-separating forces from the vertical stresses induced by the workpieceAs such back-up rolls are often used to counter this phenomenon
Another method to reduce or eliminate elastic roll deflection is to usematerials of high elastic modulus such as sintered carbide for thework rolls
A more common method to counter the effects of roll bending is theusage of cambered rolls The degree of cambering depends on thewidth of the metal piece flow stress of the material and the reductionper pass However certain problems arise with improper work rollscambering
10731
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Lack of camber or insufficient cambering of the work rolls results inproducing a workpiece that has a thicker center than the edge The thickercenter implies that the edges are plastically elongated more than the centerThis induces a residual stress pattern of compression at the edges and tensionalong the centerline of the workpiece (Figure a) The consequences of thisuneven distribution of stress within the workpiece can be centerline cracking(Figure b) warping (Figure c) or edge wrinkling (Figure d) of the final metalsheet
Figure a
Figure d Figure c
Figure b
10732
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
In the case where the work rolls are over-cambered the edges of theworkpiece will be thicker than the center and the residual stress pattern isexactly the opposite of that of insufficient cambering ie tension at the edgesand compression along the centerline (Figure e) Possible undesirable resultsof the workpiece being produced in such a manner are edge cracking (Figuref) splitting (Figure g) or centerline wrinkling (Figure h)
Figure e Figure f
Figure g Figure h
10733
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Schematic Illustration of Various Roll arrangements
10734
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Schematic Illustration of various roll arrangements (a) Two-high (b) Three-high
(c) Four-high (d) Cluster mill
10735
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Shape-Rolling OperationsVarious shapes can be produced by shape rolling Bars Channels I-beams Railroad rails
Roll-pass design requires considerable experience in order to avoidexternal and internal defects
10736
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Stages in Shape Rolling of an H-section part Various other structuralsections such as channels and I-beams are rolled by this kind of process
10737
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Ring Rolling
A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together
The ring shaped blank my be produced by Cutting from plate Piercing Cutting from a thick walled pipe
Various shapes can be produced by shaped rollsTypical applications of ring rolling Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races
Can be carried out at room temperatureHas short production timeClose dimensional tolerances
10738
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Thread Rolling
Cold-forming processStraight or tapered threads are formed on round rods by passing the pipethough diesTypical products include Screws and Bolts
Threads are rolled in the soft conditionThreads may then be heat treated and subjected to final machining orgrindingUncommon or special-purpose threads are machined
10739
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Production of Seamless Pipe amp Tubing
Rotary tube piercing (Mannesmann process)
Hot-working process
Produces long thick-walled seamless pipe
Carried out by using an arrangement of rotating rolls
Tensile stresses develop at the center of the bar when it is subjected tocompressive forces
10740
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering 10741
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Continuous Casting amp Integrated Mills and MinimillsContinuous casting Advantages
Highly automatedReduces product costCompanies are converting over to this type of casting
Integrated Mills utilize everything from the production of hot metal to thecasting and rolling of the finished productMinimills Scrap metal is melted Cast continuously Rolled directly into specific lines of products Each minimill produces one kind of rolled product
RodBarStructural steel
10742
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Continuous Casting
10743
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Salient Points about Rolling
Rolling is the most extensively used metal forming process and its share isroughly 90
The material to be rolled is drawn by means of friction into the tworevolving roll gap
The compressive forces applied by the rolls reduce the thickness of thematerial or changes its cross sectional area
The geometry of the product depend on the contour of the roll gap
Roll materials are cast iron cast steel and forged steel because of highstrength and wear resistance requirements
Hot rolls are generally rough so that they can bite the work and cold rollsare ground and polished for good work finish
In rolling the crystals get elongated in the rolling direction In cold rollingcrystal more or less retain the elongated shape but in hot rolling they startreforming after coming out from the deformation zone
10744
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
The peripheral velocity of rolls at entry exceeds that of the strip which isdragged in if the interface friction is high strip enough
In the deformation zone the thickness of the strip gets reduced and itelongates This increases the linear speed of the strip at the exit
Thus there exist a neutral point where roll speed and strip speeds areequal At this point the direction of the friction reverses
When the angle of contact exceeds the friction angle the rolls cannot drawfresh strip
Roll torque power etc increase with increase in roll work contact lengthor roll radius
10745
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
LECTURE-03 BULK DEFORMATION
PROCESSES - FORGING
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Forging
Forging is a deformation process in which the work is compressed betweentwo dies using either impact or gradual pressure to form the part Todayforging is an important industrial process used to make a variety of high-strength components for automotive aerospace and other applications Thesecomponents include engine crankshafts and connecting rods gears aircraftstructural components and jet engine turbine parts In addition steel andother basic metals industries use forging to establish the basic forms of largecomponents that are subsequently machined to final shape and dimensions
Either impact or gradual pressure is used in forging The distinction derivesmore form the type of equipment used than differences in process technologyA forging machine that applies an impact load is called a forging hammerwhile one that applies gradual pressure is called a forging press Anotherdifference among forging operations is the degree to which the flow of thework metal is constrained by the dies By this classification there are threetypes of forging operations like
Open-die forging
Impression or Close die forging
Flashless Forging
10747
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Most forging processes begin with open die forging Opendie forging is hot mechanical forming between flat orshaped dies in which the metal flow is not completelyrestricted The stock is laid on a flat anvil while the flatface of the forging hammer is struck against the stock Theequipment may range from the anvil and hammer to gianthydraulic pressesOpen-die hot forging is an important industrial processShapes generated by open-die operations are simpleexamples include shafts disks and rings In someapplications the work must often be manipulated (forexample rotating in steps) to effect the desired shapechange Open-die forging process is shown in the followingFigure The skill of the human operator is a factor in thesuccess of these operations Operations classified as open-die forging or related operations include
FulleringEdging andCogging
Open-Die Forging
10748
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Fullering is a forging operation performed toreduce the cross section and redistribute the metalin a workpart in preparation for subsequent shapeforging It is accomplished by dies with convexsurfaces Fullering die cavities are often useddesigned into multicavity impression dies so thatthe starting bar can be rough formed before finalshaping
Edging is similar to fullering except that the dieshave concave surfaces
Cogging operation consists of a sequence of forgingcompressions along the length of a workpiece toreduce cross section and increase length It is usedin the steel industry to produce blooms and slabsfrom cast ingots It is accomplished using open dieswith flat or slightly contoured surfaces The termincremental forging is sometimes used for thisprocess
Fullering
Edging
Cogging
10749
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Simplest type of forging Dies are inexpensive Wide range of part sizes ranging from 30-1000lbs Good strength qualities Generally good for small quantities
Limitations Simple shapes only difficult to hold close tolerances machining necessary low production rate poor utilization of material high skill required
10750
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
In impression-die forgingso0metimes called closed die forgingthe die surfaces contain a shape orimpression that is imparted to thework during compression thusconstraining metal flow to asignificant degree as shown infollowing Figure In this type ofoperation a portion of the work metalflows beyond the die impression toform flash and must be trimmed offlater The process is shown in thefollowing Figure as a three stepsequence The raw workpiece isshown as a cylindrical part similar tothat used in the previous open-dieoperation
Impression or Close Die Forging
10751
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages Good utilization of material Better properties than Open Die Forgings Dies can be made of several pieces and inserts to create more advanced
parts Presses can go up to 50000 ton capacities Good dimensional accuracy High production rates Good reproducibility
Limitations High die cost Machining is often necessary Economical for large quantities but not for small quantities
10752
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Flashless Forging
Flashless forging is sometimes called closed-die forging inindustry terminology However there is a technical distinctionbetween impression-die forging and true closed-die forging Thedistinction is that in closed-die forging the raw workpiece iscompletely contained within the die cavity during compressionand no flash is formed This process is shown in the followingfigure Flashless forging imposes requirements on process controlthat are more demanding than impression-die forging Mostimportant is that the work volume must equal the space in the diecavity within a very close tolerance If the starting blank is toolarge excessive pressures may cause damage to the die or even thepress If the blank is too small the cavity will not be filledBecause of the special demands made on flashless forging theprocess lends itself best to part geometries that are usually simpleand symmetrical and to work materials such as aluminum andmagnesium and their alloys Flashless forging is often classified asa precision forging process
10753
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Advantages and Limitations
Advantages
Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster
production Typical applications are gears connecting rods and turbine blades Common materials used in precision forging are aluminum
magnesium alloys steel and titanium
Limitations
High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blankrsquos volume and shape Accurate positioning of the Blank in the die cavity
10754
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Other Forging Operations
Coining Coining is a forgingprocess by which very fine andintricate details can be createdon the surface of a metal workpiece Coining may be used tocontrol surface quality anddetail on parts One commonuse of coining as the namesuggests is in the production ofcoins
This is a flashless precision forging operation that due to the requiredaccuracy of the process is performed cold Lubrication is not used since anysubstance between the die and work would hinder the reproduction of themost accurate details that are to be formed on the works surface In thecoining process a large amount of force is exerted on the forging over a shortdistance Mechanical presses are often used for these operations
10755
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Upsetting Upsetting is a deformation operation in which a cylindricalworkpart is increased in diameter and reduced in length However as anindustrial operation it can also be performed as closed-die forging as shownin the following Figure Upsetting is widely used in the fastener industry toform the heads of nails bolts and similar hardware products
10756
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Heading The following Figure illustrates a variety of heading applicationsindicating various possible die configurations Owing to these types ofapplications more parts are produced by upsetting than any other forgingoperation It is performed as a mass production operation - cold warm orhot - on special upset forging machines called headers or formers
Care must be taken so that work piece does not buckle
Can be highly automated
10757
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Swaging and Radial Forging Swaging and radial forging are forgingprocesses used to educe the diameter of a tube or solid rod Swaging is oftenperformed on the end of a workpiece to create a tapered section The swagingprocess shown is accomplished by means of rotating dies that hammer aworkpiece radially inward to taper it as the workpiece is fed into the dies
Radial forging is similar to swaging in its action against the work and isused to create similar shapes The difference is that in radial forging the diesdo not rotate around the workpiece instead the work is rotated at it feedsinto the hammering dies
10758
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Roll Forging Roll forging is a deformation process used to reduce the cross sectionof a cylindrical (or rectangular) workpiece by passing it through a set of opposing rollsthat have grooves matching the desired shape of the part The typical operation isshown in the following Figure Roll forging is generally classified as a forging processeven though it utilizes rolls The rolls do not turn continuously in roll forging butrotate through only a portion of one revolution corresponding to the desireddeformation to be accomplished on the part Roll-forged parts are generally strongerand possess favorable grain structure compared to competing processes such asmachining that might be used to produce the same part geometry
10759
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Forging Machines
Equipment used in forging consists of forging machines classified asforging hammers and presses and forging dies which are thespecial tooling used in these machines In addition auxiliary equipment isneeded such as furnaces to heat the work mechanical devices to load andunload the work and trimming stations to cut away the flash inimpression-die forging
Forging Hammers Forging hammers operate by applying an impactload against the work The term drop hammer is often used for thesemachines owing to the means of delivering impact energy Drop hammersare most frequently used or impression-die forging The upper portion ofthe forging die is attached to the ram and the lower portion to the anvilIn the operation the work is placed on the lower die and the ram is liftedand then dropped When the upper die strikes the work the impact energycauses the part to assume the form of the die cavity
10760
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Drop hammers can be classified asgravity drop hammers and powerdrop hammers
Gravity drop hammers achievetheir energy by the falling weight of aheavy ram The force of the blow isdetermined by the height of the dropand the weight of the ram
Power drop hammers acceleratethe ram by pressurized air or steamOne disadvantage of the drophammers is that a large amount of theimpact energy is transmitted throughthe anvil and into the floor of thebuilding This results in a great dealof vibration for the surrounding area
Power drop hammers
Gravity drop hammers
10761
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Forging Presses Presses apply gradual pressure rather than suddenimpact to accomplish the forging operation Forging presses include
Mechanical Presses
Hydraulic Presses and
Screw Presses
Mechanical presses typically operate by means of eccentrics cranks orknuckle joints which convert the rotating motion of a drive motor into thetranslational motion of the ram These mechanisms are very similar tothose used in stamping presses Mechanical presses typically achieve veryhigh forces at the bottom of the forging stroke
6462
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Knuckle Joint Press Crank Press Eccentric Press
6463
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Hydraulic presses The basic working principlesof the hydraulic press are simple and rely ondifferences in fluid pressure Fluid is pumped intothe cylinder below the piston this causes the fluidpressure under the piston to increaseSimultaneously fluid is pumped out of the topchannel causing the fluid pressure above the pistonto decrease A higher pressure of the fluid below thepiston than the fluid above it causes the piston torise In the next step fluid is pumped out frombelow the piston causing the pressure under thepiston to decrease Simultaneously fluid is pumpedinto the cylinder from the top this increases thefluid pressure above the piston A higher pressureof the fluid above the piston than the fluid below itmoves the piston downward
6464
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Screw Presses Forging screw pressesuse the rotational energy of a motor toturn a large screw Typically a friction diskis used to translate the force from thedrive shaft to the screws head The screwpushes a ram with great mechanicaladvantage Screw presses are similar tohydraulic presses in that they arerelatively slow and require a longercontact with the work Screw presses arealso similar to hydraulic presses in thatthey can produce a constant amount offorce over a long stroke Some screw pressmachines in modern industry can produce31000 tons (62000000 lbs) of force
6465
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering 10766
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
LECTURE-04 BULK DEFORMATION
PROCESSES - EXTRUSION
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Extrusion Process
Extrusion is a process that forces metal or plastic to flow through a shapedopening die The material is plastically deformed under the compression in thedie cavity The process can be carried out hot or cold depending on the ductilityof the materialThe tooling cost and setup is expensive for the extrusion process but theactual manufactured part cost is inexpensive when produced in significantquantitiesMaterials that can be extrudes are aluminum copper steel magnesium andplastics Aluminum copper and plastics are most suitable for extrusion
10768
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Classification of Extrusion Processes
Depending on the ductility of the material used extrusions can be caries outvarious ways
Hot Extrusion Extrusion carried out at elevated temperatures
Forward or direct extrusion and
Backward or indirect extrusion
Cold Extrusion Extrusion carried out a ambient temperature Oftencombined with forging operations
Hydrostatic Extrusion Pressure is applied by a piston throughincompressible fluid medium surrounding the billet
10769
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Hot Extrusion
Extrusion is carried out at elevated temperatures-for metals and alloys that do not havesufficient ductility at room temperature or in order to reduce the forces required In thisextrusion die wear can be excessive and cooling of the hot billet in the chamber can be aproblem which results in highly non-uniform deformation To reduce cooling of the billetand to prolong die life extrusion dies may be preheated as is done in hot forgingoperations Hot billet causes the following problems
Because the billet is hot it develops an oxide film unless heated in an inert-atmosphere furnace This film can be abrasive and it can affect the flow pattern ofthe material
It also results in an extruded product that may be unacceptable in cases in whichgood surface finish is important
In order to avoid the formation of oxide films on the hot extruded product the dummyblock placed ahead of the ram is made a little smaller in diameter than the container As aresult a thin cylindrical shell consisting mainly of the oxidized layer is left in thecontainer The extruded product is thus free of oxides the skull is later removed from thechamber Hot extrusion can be done by
Forward or direct extrusion process
Backward or indirect extrusion process
10770
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Direct Extrusion In this extrusion process the heated billet is placed in the container Aram towards the die pushes it The metal is subjected to plastic deformation slides alongthe walls of the container and is forced to flow through the die opening At the end of theextruding operation a small piece of metal called butt-end scrap remains in the containerand cannot be extruded
Indirect Extrusion For the production of solid part the die is mounted on the end of ahollow ram and enters the container as shown in the following Figure the outer end ofcontainer being closed by a closure plate As the ram travels the die applies pressure on thebillet and the deformed metal flows through the die opening in the direction opposite to theram motions and the product is extruded through the hollow ram In indirect extrusionthere is practically no slip of billet with respect to the container walls
Direct ExtrusionExtrusion
Indirect Extrusion10771
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Cold Extrusion
This process is similar to hot extrusion except that the metals worked possess theplasticity necessary for successful forming without heating them Usually these metalshave a high degree of ductility Cold extrusion is also done to improve the physicalproperties of a metal and to produce a finished part Cold extrusion is done mostly onvertical mechanical presses because they are fast and simple The method is fastwastes no or little materials and gives higher accuracy and tolerance The widelyemployed cold extrusion method is Impact extrusion Impact extrusion isperformed at higher speeds and shorter strokes than conventional extrusion It is formaking discrete parts For making thin wall-thickness items by permitting largedeformation at high speed
Backward impact extrusion Forward impact extrusion Combined impact extrusion
10772
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Hydrostatic Extrusion
With the hydrostatic extrusion the billet in the container issurrounded with fluid media is called also hydrostaticsmedium The container space is sealed on the stem side andon the die side so that the penetrating stem can compress thehydrostatics medium on pressing power without the stemtouches the billet Also during extrusion the stem does nottouch the billet The rate with which the billet moves whenpressing in the direction of the die is thus not equal to theram speed but is proportional to the displaced hydrostaticsmedium volume For this process it is substantial that thebillet seals the container space on applying the pressingpower in the hydrostatics medium against the die sinceotherwise the pressing power cannot be developed
It is thus a conical die and a careful sharpening billet a prerequisite of the processSince the billet does not touch the containers wall but between billet and containerhydrostatics medium exists prevails negligibly small friction of a liquid at the billetsurface Only the friction between billet and die is of importance for the deformingprocess Likewise pressing of the billet is unnecessary at the press begin
10773
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Tube-Drawing
Tube-drawing operations with and without an internal mandrel Note that a variety ofdiameters and wall thicknesses can be produced from the same initial tube stock
10774
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Extrusion Defects
Surface Cracking Cracking on billet materials occurs due totemperature friction punch speed High Temperatures
Crack from along the grain boundaries Typically occur inaluminum magnesium zinc alloys
Cold TemperaturesCaused by sticking of billet material at the die landKnown has the ldquoBamboo Defectrdquo because of its similar appearanceto bamboo
Pipe The metal-flow pattern tends to draw oxides and impurities towardthe center of the billetInternal Cracking Center of extruded product develops cracks Attributed to a state of hydrostatic tinsel stress Cracks increase with increasing die angle impurities and decreasing
extrusion ratio and friction
10775
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Advantages of Extrusion Processes
The range of extruded items is very wide Cross-sectional shapes not possible byrolling can be extruded such as those with re-entrant sections
No time is lost when changing shapes since the dies may by readily removed andreplaced
Dimensional accuracy of extruded parts is generally superior to that of rolled ones
In extrusion the ductility of the metals is higher as the metal in the container is incomposite compression this advantage being of particular importance in workingpoorly plastic metals and alloys
Very large reductions are possible as compared to rolling for which the reductionper pass is generally 2
Automation in extrusion is simpler as items are produced in a single passing
Small parts in large quantities can be made For example to produce a simplepump gear a long gear is extruded and then sliced into a number of individualgears
It does not need draft or flash to trim and needless machining as it is more accuratethan forging
10776
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Disadvantages of Extrusion Processes
Process waste in extrusion is higher than in rolling where it is only 1 to 3
In-homogeneity in structure and properties of an extruded product isgreater due to different flows of the axial and the outer layers of blanks
Service life of extrusion tooling is shorter because of high contact stressesand slip rates
Relatively high tooling costs being made from costly alloy steel
In productivity extrusion is much inferior to rolling particularly to itscontinuous varieties
Cost of extrusion are generally greater as compared to other techniques
10777
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Applications of Extrusion Processes
Extrusion is more widely used in the manufacture of solid and hollowsections from poorly plastic non-ferrous metals and their alloys(aluminum copper brass and bronze etc)
Steel and other ferrous alloys can also be successfully processed with thedevelopment of molten-glass lubricants
Manufacture of sections and pipes of complex configuration
Medium and small batch production
Manufacture of parts of high dimensional accuracy
The range of extruded items is very wide rods from 3 to 250 mm indiameter pipes of 20 to 400 mm in diameter and wall thickness of 1 mmand above and more complicated shapes which can not be obtained byother mechanical methods
10778
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
LECTURE-05 SHEET METAL FORMING
PROCESSES
Nikhil R Dhar Ph DProfessor IPE Department
BUET
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Introduction
Sheet metal forming is a grouping of manycomplementary processes that are used toform sheet metal parts One or more of theseprocesses is used to take a flat sheet of ductilemetal and mechanically apply deformationforces that alter the shape of the materialBefore deciding on the processes one shoulddetermine whether a particular sheet metalcan be formed into the desired shape withoutfailure The sheet metal operations done on apress may be grouped into two categoriescutting (shearing) operations andforming operations
Sheet Metal Forming
10780
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering 10781
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Cutting (Shearing) Operations
In this operation the workpiece is stressed beyond its ultimate strength Thestresses caused in the metal by the applied forces will be shearing stressesThe cutting operations include
Punching (Piercing)
Blanking
Notching
Perforating
Slitting
Lancing
Parting
Shaving
Trimming
Fine blanking
10782
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Punching (Piercing) It is a cutting operation by which various shaped holes aremade in sheet metal Punching is similar to blanking except that in punching thehole is the desired product the material punched out to form the hole being waste
Blanking Blanking is the operation of cutting a flat shape sheet metal The articlepunched out is called the blank and is the required product of the operation Thehole and metal left behind is discarded as waste
10783
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Notching This is cutting operation by which metal pieces are cut from the edge of a sheetstrip or blank
Perforating This is a process by which multiple holes which are very small and closetogether are cut in flat work material
Slitting It refers to the operation of making incomplete holes in a workpiece
Lancing This is a cutting operation in which a hole is partially cut and then one side is bentdown to form a sort of tab Since no metal is actually removed there will be no scrap
Parting Parting involves cutting a sheet metal strip by a punch with two cutting edges thatmatch the opposite sides of the blank
10784
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Shaving The edge of blanked parts is generally rough uneven and unsquareAccurate dimensions of the part are obtained by removing a thin strip of metalalong the edges
Trimming This operation consists of cutting unwanted excess material from theperiphery of previously formed components
Fine blanking Fine blanking is a operation used to blank sheet metal parts withclose tolerances and smooth straight edges in one step
(a) Shaving a sheared edge (b) Shearing and
shaving combined in one strokeFine blanking
10785
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Shearing Dies
Because the formability of a sheared part can be influenced by the quality of its shearededges clearance control is important In practice clearances usually range between 2 and8 of the sheetrsquos thickness generally the thicker the sheet the larger is the clearance (asmuch as 10) However the smaller the clearance the better is the quality of the edgeSome common shearing dies are describe below
Punch and Die Shapes As the surfaces of the punch and die are flat thus the punchforce builds up rapidly during shearing because the entire thickness of the sheet issheared at the same time However the area being sheared at any moment can becontrolled be beveling the punch and die surfaces as shown in the following FigureThis geometry is particularly suitable for shearing thick blanks because it reduces thetotal shearing force
Examples of the use of shear angles on punches and dies
10786
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Compound Dies Several operations on the same strip may be performed in onestroke with a compound die in one station These operations are usually limited torelatively simple shearing because they are somewhat slow and the dies are moreexpensive than those for individual shearing operations
10787
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Progressive Dies Parts requiring multiple operations such as punchingblanking and notching are made at high production rates in progressive dies Thesheet metal is fed through a coil strip and a different operation is performed at thesame station with each stroke of a series of punches
10788
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Transfer Dies In a transfer die setup the sheet metal undergoes differentoperations at different stations which are arranged along a straight line or acircular path After each operation the part is transfer to the next operation foradditional operations
10789
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Forming Operations
In this operation the stresses are below the ultimate strength of the metal In thisoperation there is no cutting of the metal but only the contour of the workpiece ischanged to get the desired product The forming operations include
Bending In this operation the material in the form of flat sheet orstrip is uniformly strained around a linear axis which lies in theneutral plane and perpendicular to the lengthwise direction of thesheet or metal The bending operations include
V-bendingEdge bendingRoll bendingAir bendingFlangingDimpling
Press break formingBeadingRoll formingTube formingBulgingStretch forming
Drawing This is a process of a forming a flat workpiece into a hollow shape by meansof a punch which causes the blank to flow into die cavity
Squeezing Under this operation the metal is caused to flow to all portions of a diecavity under the action of compressive forces
10790
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
V-bending Edge bending Roll bending
Bending in 4-slide machine Air bending
Bending of Flat Sheet and Plate
10791
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Flanging Flanging is a process of bending the edges of sheet metals to 90o
Shrink flanging ndash subjected to compressive hoop stress
Stretch flanging ndashsubjected to tensile stresses
10792
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Dimpling
First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle lt 90 degrees as in fitting conical ends its called
flanging
10793
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Press Break Forming Sheet metal or plate can be bent easily with simplefixtures using a press Long and relatively narrow pieces are usually bent in a pressbreak This machine utilizes long dies in a mechanical or hydraulic press and issuitable for small production runs The tooling is simple and adaptable to a widevariety of shapes
10794
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
(a) Bead forming with a single die
Beading In beading the edge of the sheet metal is bent into the cavity of a dieThe bead gives stiffness to the part by increasing the moment on inertia of theedges Also it improves the appearance of the part and eliminates exposed sharpedges
(b) Bead forming with two dies in a press brake
10795
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Roll-forming process
Roll Forming For bending continuous lengths of sheet metal and for largeproduction runs roll forming is used The metal strip is bent in stages by passing itthrough a series of rolls
Stages in roll forming of a sheet-metal door frame In Stage 6 the rolls may be shaped as in A or B
10796
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Bulging The basic forming process of bulging involves placing tabular conical orcurvilinear part into a split-female die and expanding it with say a polyurethane plugThe punch is then retracted the plug returns to its original shape and the part isremoved by opening the dies
(a) Bulging of a tubular part with a flexible plug Water pitchers can be made by this method
(b) Production of fittings for plumbing byexpanding tubular blanks with internal pressure
(c) Manufacturing of Bellows
10797
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die
Rubber Forming In rubber forming one of the dies in a set is made of flexiblematerial such as a rubber or polyurethane membrane Polyurethanes are usedwidely because of their resistance to abrasion long fatigue life and resistance todamage by burrs or sharp edges of the sheet blank In bending and embossingsheet metal by the rubber forming method as shown in the following Figure thefemale die is replaced with a rubber pad Parts can also be formed with laminatedsheets of various nonmetallic material or coatings
10798
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Hydroform Process In hydroforming or fluid forming process the pressureover the rubber membrane is controlled throughout the forming cycle withmaximum pressure reaching 100 Mpa This procedure allows close control of thepart during forming to prevent wrinkling or tearing Hydroforming processes havethe following advantages Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes
10799
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Explosive Forming Process Explosive forming is distinguished from
conventional forming in that the punch or diaphragm is replaced by an explosivecharge The explosives used are generally high explosive chemicals gaseousmixtures or propellants There are two techniques of high explosive forming suchas Contact technique and Stand -off technique
Contact Technique The explosive charge in theform of cartridge is held in direct contact with thework piece while the detonation is initiated Thedetonation builds up extremely high pressures (upto30000MPa) on the surface of the work pieceresulting in metal deformation and possiblefracture The process is used often for bulging tubes
107100
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Standoff Technique The sheet metal work piece blank is clamped over a dieand the assembly is lowered into a tank filled with water The air in the die ispumped out The explosive charge is placed at some predetermined distance fromthe work piece On detonation of the explosive a pressure pulse of very highintensity is produced A gas bubble is also produced which expands spherically andthen collapses When the pressure pulse impinges against the work piece themetal is deformed into the die with as high velocity as 120 ms
107101
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Deep Drawing Drawing operation is the process of forming a flat piece ofmaterial (blank) into a hollow shape by means of a punch which causes the blankto flow into the die-cavity Round sheet metal block is placed over a circular dieopening and held in a place with blank holder amp punch forces down into the diecavity Wrinkling occurs at the edges
Deep-drawing process on a circular sheet-metal blank
107102
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Ironing Process If the thickness of the sheet as it enters the die cavity is morethan the clearance between the punch and the die the thickness will have to bereduced this effect is known as ironing Ironing produces a cup with constant wallthickness thus the smaller the clearance the greater is the amount of ironing
Schematic illustration of the ironing process Note that the cup wallis thinner than its bottom All beverage cans without seams areironed generally in three steps after being deep drawn into a cup
107103
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Redrawing Operations Containers or shells that are too difficult to draw in one operationare generally redrawn In reverse redrawing shown in following Figure the metal issubjected to bending in the direction opposite to its original bending configuration Thisreversal in bending results in strain softening This operation requires lower forces thandirect redrawing and the material behaves in a more ductile manner
Conventional redrawing Reverse redrawing
107104
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Beverage Can
Steps in Manufacturing an
Aluminum Can
107105
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
Aluminum Two-Piece Beverage Cans
107106
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION
Department of Industrial amp Production Engineering
THANK YOU FOR YOUR ATTENTION