Lecture 1 metal_forming
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Transcript of Lecture 1 metal_forming
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FUNDAMENTALS OF METAL FORMING
Overview of Metal FormingMaterial Behavior in Metal Forming
Temperature in Metal Forming.Hot working and cold working operations.
Smithy, Smithy Tools, forging operations
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Metal Forming
Large group of manufacturing processes in which plastic deformation is used to change the shape of metal workpieces
The tool, usually called a die, applies stresses that exceed yield strength of metal
The metal takes a shape determined by the geometry of the die
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Stresses in Metal FormingStresses to plastically deform the metal are
usually compressiveExamples: rolling, forging, extrusion
However, some forming processes Stretch the metal (tensile stresses)Others bend the metal (tensile and
compressive)Still others apply shear stresses
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Material Properties in Metal Forming
Desirable material properties: Low yield strength and high ductility
These properties are affected by temperature: Ductility increases and yield strength
decreases when work temperature is raisedOther factors:
Strain rate and friction
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Temperature in Metal Forming Any deformation operation can be
accomplished with lower forces and power at elevated temperature
Three temperature ranges in metal forming: Cold workingWarm workingHot working
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Hot WorkingDeformation at temperatures above
recrystallization temperature Recrystallization temperature = about
one‑half of melting point on absolute scale In practice, hot working usually performed
somewhat above 0.5Tm
Metal continues to soften as temperature increases above 0.5Tm, enhancing advantage of hot working above this level
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Why Hot Working?Capability for substantial plastic deformation of
the metal ‑ far more than possible with cold working or warm working
Why?Strength coefficient is substantially less than at
room temperatureStrain hardening exponent is zero
(theoretically)Ductility is significantly increased
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Warm WorkingPerformed at temperatures above room
temperature but below recrystallization temperature
Dividing line between cold working and warm working often expressed in terms of melting point: 0.3Tm, where Tm = melting point (absolute
temperature) for metal
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Advantages of Warm WorkingLower forces and power than in cold workingMore intricate work geometries possibleNeed for annealing may be reduced or
eliminated
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Advantages of Hot Working vs. Cold WorkingWorkpart shape can be significantly alteredLower forces and power requiredMetals that usually fracture in cold working
can be hot formedStrength properties of product are generally
isotropicNo strengthening of part occurs from work
hardening Advantageous in cases when part is to be
subsequently processed by cold forming
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Disadvantages of Hot WorkingLower dimensional accuracyHigher total energy required (due to the
thermal energy to heat the workpiece)Work surface oxidation (scale), poorer
surface finishShorter tool life
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Cold WorkingPerformed at room temperature or slightly
above Many cold forming processes are important
mass production operationsMinimum or no machining usually required
These operations are near net shape or net shape processes
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HOT WORKING OPERATIONSFORGINGROLLINGWELDINGEXTRUSIONSPINNINGHOT PIERCING AND ROLLING
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COLD WORKING OPERATIONSCOLD ROLLINGEXTRUSIONPRESSING DEEP DRAWINGSQUEEZINGBENDINGSHEARING
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Figure 18.2 – Basic bulk deformation processes: (a) rolling
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Figure 18.2 – Basic bulk deformation processes: (b) forging
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Figure 18.2 – Basic bulk deformation processes: (c) extrusion
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Figure 18.2 – Basic bulk deformation processes: (d) drawing
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Sheet MetalworkingForming and related operations performed
on metal sheets, strips, and coilsHigh surface area‑to‑volume ratio of starting
metal, which distinguishes these from bulk deformation
Often called pressworking because presses perform these operationsParts are called stampingsUsual tooling: punch and die
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Figure 18.3 ‑ Basic sheet metalworking operations: (a) bending
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Figure 18.3 ‑ Basic sheet metalworking operations: (b) drawing
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Figure 18.3 ‑ Basic sheet metalworking operations: (c) shearing
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SMITHY&FORGINGDIFFERENCES BETWEEN SMITHY AND
FORGING
SMITHY – HAND OPERATED -METAL IS DEFORMED INTO THE DESIRED SHAPE BY HAMMERING, PRESSING AND BENDING USING HAND OPERATED TOOLS.
FORGING– MACHINE OPERATED – METAL IS DEFORMED INTO THE DESIRED SHAPE BY HAMMERING , PRESSING AND BENDING USING POWER OPERATED MACHINES.
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FORGING AND SMITHYSMITHY PROCESS IS CARRIED BY HAND
OPERATED TOOLSFORGING IS CARRIED BY POWER
OPERATED TOOLS.SMITHY IS CARRIED FOR SMALL JOBS AND
FORGING IS FOR HEAVY WORK AND MASS PRODUCTION
FOR FORGING, SHAPES ARE ALSO PRE DEFINED IN FORM OF DIES, WHERE AS FOR SMITHY, REQUISTE SHAPES ARE GENERATED BY THE REPETITVE PROCESS REPETITIVE USE OF HAND TOOLS.
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Black smith toolsAnvilSwage blockHammersTongsChiselsSwagesFullersFlattersPunches
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BLACK SMITH FORGE
Black Smith Forge
Heating of metal is done in hearth or furnance
It is shallow dish or tray of Mild steel with lining of fire clay or refractory material to withstand heat during combustion of fuel.
Open hearth and closed hearth (open fire &stock fire)
Smoke or gas are escaped through hood or chimney
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WORKING OF FURNANCEAir at pressure for
combustion of fuel.Centrifugal fan is
driven by electrical motor.
It draws air from atmiosphere and delivers at high pressure to furnance
It is mainly used for maintaining combustion of fuel in furnance,.
Standard coal forge
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ANVILIt is made of solid
wrought iron or cast steel.
It is a supporting the hot metal pieces to be forged.
Tools like swages or fullers are inserted into the holes
Bick or horn of the anvil is used for bending
Forging operations are carried out on the face of the anvil
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SWAGE BLOCKSolid or rectangular
block cast steel or forged steel.
Used for swaging, bending,finishing various workpieces.
Workpiece is given rough shape on anvil , reheated placed in a similar shaped recess in the side of the swage block.
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TONGSTongs are used for
gripping and turning hot metal workpieces during forging.
Tong length : 475 – 600 mm length
Bit length - 75-120 mmMaterial : 0.4% carbon.Types: Pick up tong,
square tong, round tong flat tong, 16 types of tongs used to accomdate different sized and shaped workpieces.
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HAMMER Hammer used by smith for striking and to give
required shape to hot metal work piece.Hand hammer – small and light components.Types :Ball pein hand hammer : Face : general striking,
ball pien is used for riveting or burring over work.
Cross pein hammer: cross : hammmering streching, bending into inside shape of component.
Straight peen hammer: : It is used for stretching the metal
Sledge hammer.:Heavier hammer, used for flattening.
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Ball Peen hammer
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Straight Peen hammer
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CROSS PIN HAMMER
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Pneumatic hammerSmall parts by hand
hammersHeavy machine parts require
great degree of deformationHand forging lengthy
processMachines which works on
the principle of repeated blows - power or forging hammers.
Spring HammerAir HammerSteam hammerDrop hammer
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Steam hammer
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swagesThey are used in
pairs.Employed to reduce
and finish the job to size or shape, round or heaxgonal.
Small jobs , swages are used, large work, swage blocks are used.
During swaging, hot metal is rotated between the swages.
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FULLERSIt is set of two toolsTop tool is provided with handle and bottom has a square shank. Fits into square hole.
Fullers are used to form grooves, stretch or draw the metal and reduce the thickness of the workpiece.
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FORGING OPERATIONS
UpsettingDrawingCuttingBendingPunchingWeldingSetting down
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UPSETTING OPERATIONIt is carried out to
increase the thickness of bar and reduce its length.
Ex: Bolt HeadBlow of the hammer
must be in line with the bar to prvent bending of the bar.
Hot bar must be in line with the bar to prevent bending of the bar.
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UPSETTING
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DRAWING OPERATIONTo reduce
thickness and increase its thickness.
It is carried out by working the metal over the horn of the anvil then hammering on the anvil face.
For heavy work, fullers are used
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PUNCHINGThe punch is driven part way through the workpiece with hammer blows.
The Work is turned over and the hole is completed from the other side.
PUNCHING OPERATION
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BENDING OPERATIONBending is a common forging operation.
Simple process is the bending a piece of metal, is to support it on the anvil/Die and to strike its free end with a hammer.
When bent , workpiece thins out round bend causing weakness.
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Flatting and Setting DownFlattening leaves the a corrugated
surface on the job.The marks of the hammer remains on
the surface , and the removal of its is called flatter.
Flatting and setting down used to finish off to a good smooth surface.
Flatter is used for smoothening flat surfaces,
Set hammer is used in restricted areas, such as corners and bends.
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FORGE WELDINGLow carbon and
wrought steel can satisfactorily forge welded.
Welding possible above 30mm thickness.
Parts are heated to stage of plastic and placed ebd to end and hammered manually or by power hammer
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IMPORTANT QUESTIONSDefine metal forming operations?
What is difference between Hot working and cold working operations?
Name the various processes of metal forming operations.
What is the difference between smithy and forging?
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IMPORTANT QUESTIONSWhat is the significance of hammers in forging?
Explain the major tools used in smithy?
What is the application difference between fuller and swage?
What are the major forging operations?
What is the difference between Upsetting and drawing operations?