Study of Operational Concepts of Study of Operational Concepts of Conventional and CNC Machines - Conventional and CNC Machines -

Lathe & MillingLathe & Milling

Pratik BasuPratik Basu

Final year B.E studentFinal year B.E student

Lingaya’s Inst. Of Mgmt. & Tech.Lingaya’s Inst. Of Mgmt. & Tech.

OverviewOverview

I had the opportunity to study both conventional and I had the opportunity to study both conventional and CNC machines, but have given more stress on the CNC CNC machines, but have given more stress on the CNC machines, owing to their emerging importance. A general machines, owing to their emerging importance. A general description of conventional lathe and milling machines description of conventional lathe and milling machines has been given. The concepts of Computer Numerically has been given. The concepts of Computer Numerically Controlled machines have been explained in greater Controlled machines have been explained in greater detail.detail.

ABOUT NPLABOUT NPL National Physical Laboratory (NPL), New Delhi is the premier National Physical Laboratory (NPL), New Delhi is the premier

research laboratory in India in the field of physical sciences. It is research laboratory in India in the field of physical sciences. It is under the Council of Scientific and Industrial research (CSIR) under the Council of Scientific and Industrial research (CSIR) located at the PUSA campus on Dr. K.S.Krishanan Marg, New located at the PUSA campus on Dr. K.S.Krishanan Marg, New Delhi-110012.Delhi-110012.

MAIN ACTIVITIES OF NPLMAIN ACTIVITIES OF NPLResearch and Development Research and Development

Consultancy Consultancy

Sponsored and contact researchSponsored and contact research

Calibration and TestingCalibration and Testing

Ever since its inception in 1947, NPL has made several fruitful Ever since its inception in 1947, NPL has made several fruitful contributions to the nation, society and industry as well as to building contributions to the nation, society and industry as well as to building knowledge base in its specific areas of strength in physics.knowledge base in its specific areas of strength in physics.

Workshop

NPL has a large, fully furnished Central Workshop consisting of various kinds of automated as well as manually controlled machines along with divisions like:

Electroplating Electroplating

Designing Designing

Sheet Metal workingSheet Metal working

Carpentry Carpentry

Cutting and weldingCutting and welding

Conventional machines sectionConventional machines section

CNC machines sectionCNC machines section

The workshop staff consists of skilled professional staff for producing Ultra High Precision parts. One of the most important jobs performed by the workshop is to provide the various R&D departments with the spare parts of machineries that are not easily available. This leads to saving of adequate amount of time and money.

Conventional machines sectionConventional machines sectionSome of the machines in this section are : Some of the machines in this section are :

BandsawBandsaw - The bandsaw is useful for cutting stock to size and - The bandsaw is useful for cutting stock to size and roughing out shapes. It cuts curved shapes very well.roughing out shapes. It cuts curved shapes very well.

Belt sanderBelt sander – A belt sander is used to remove rough edges. It makes – A belt sander is used to remove rough edges. It makes use of an abrasive riding belt. Effective on wood, plastic and most use of an abrasive riding belt. Effective on wood, plastic and most metals.metals.

Drilling machine Drilling machine – – The drill press is mostly The drill press is mostly used for drilling holes, used for drilling holes, reaming, boring, reaming, boring, countersinking etc.countersinking etc.

Power hacksaw – A type of hacksaw powered either by it’s own electric motor or connected to an engine.

Drilling machinePower hacksaw

And several other machines for sheet metal work, electroplating etc. , as well as callipers, micrometers etc. for measurement and testing.

• Surface grinder – It is a machine tool used to provide high precision surface finish. The grinding wheel rotates in the spindle head, it’s height adjustable. The workpiece is fed by a horizontal table positioned below the grinding wheel.

• Slotting machine - Similar to a vertical shaper. The most common use is to machine straight, flat surfaces.

Surface grinder

Slotting machine

The 2 principal conventional machines on which we are focusing are the lathe and milling machines.

Lathe MachineLathe Machine

Lathes are designed for precisely machining relatively hard materials. With their inherent versatility, they are used in a wide range of applications, and can

machine a broad range of materials.

These lathe machine removes material from a rotating work piece via the linear movements of various cutting tools, such as tool bits and drill bits.

Operations performed on a latheOperations performed on a lathe

• Turning – The diameter of a part can be reduced to desired dimension.

• Facing - A lathe can be used to create a smooth, flat, face very accurately perpendicular to the axis of a cylindrical part.

• Parting - Deeper and narrower than a turning tool. It is designed for making narrow grooves and for cutting off parts.

• Drilling - A lathe can also be used to drill holes accurately concentric with the centerline of a cylindrical part.

• Boring - Boring is an operation in which a hole is enlarged with a single point cutting tool.

• Threading - External threads can be cut with a die and internal threads can be cut with a tap.

Types of latheTypes of lathe• Centre lathe / bench lathe / engine lathe - The most basic type of lathe.

• Toolroom Lathe - Lathe optimized for toolroom work. It has all of the best optional features that may be omitted from less expensive models, such as a collet closer, taper attachment, and others.

• Turret lathes and capstan lathes - Used for repetitive production of duplicate parts.

• Multispindle lathe - Multispindle lathes have more than one spindle and automated control.

• CNC lathe - CNC lathes are rapidly replacing the older production lathes due to their ease of setting and operation. The part may be designed by the Computer-aided manufacturing (CAM) process, the resulting file uploaded to the machine, and once set and trialled the machine will continue to turn out parts under the occasional supervision of an operator.

Milling machineMilling machineA milling machine is a machine tool used for the shaping of metal and other solid materials. Its basic form is that of a rotating cutter, which rotates about

the spindle axis (similar to a drill), and a table to which the workpiece is affixed. In contrast to the lathe machine, in the milling machine the workpiece moves longitudinally against the rotating cutter. Milling machines may be operated manually or by CNC.

Types of milling cuttersTypes of milling cuttersIn vertical mills, milling cutters with solid shafts are usually used.

End mills are designed for cutting slots, keyways and pockets.

Two fluted end mills can be used to plunge into work like a drill.

Ball end mills can produce a fillet.

• Roughing• Finishing• Drilling• Boring (a) Rough (b) Finish (c) Counter boring• Slotting• Key way cutting• Gear cutting

• Spur• Bevel• Worm• Helical

Operations done on Milling machines

Computer and Numerically Controlled Computer and Numerically Controlled MachinesMachines

Numerically Controlled (NC)

NC is the operation of M/c tool by a series of coded instructions consisting of numbers, letters of the alphabets and symbols, which the MCU (Machine Control Unit) can understand.

Computer numerically controlled (CNC)

When numerical control is performed under computer supervision, it is called computer numerical control (CNC). Computers are the control units of CNC machines. A programmer enters some information in the program, but the computer calculates all necessary data to get the job done.

For both NC and CNC systems, working principles are the same. Only the way in which the execution is controlled is different. Normally, new systems are faster, more powerful, and more versatile.

Various popular CNC control systemsVarious popular CNC control systems 1. ECS2. LECS3. NUM4. SELCA5. MARPOSS6. Z-167. FANUC 8. FAGOR9. FIDIA10. DECKEL11. SINUMERIC12. HINUMERIC13. HEIDENHAIN14. GILDEMEISTER

A CNC Milling center by DECKEL

Important terms related to CNC machiningImportant terms related to CNC machining • Machine Zero - Machine zero is a point at the origin of the machine’s

coordinate measuring system. All the Axis movements and other dimensions are measured from this point. It is similar to the origin of coordinate measuring system.

• Machine reference point - It refers to the initial point of return for the purpose of measuring/feedback systems. Whenever a CNC machine is switched on the feedback system has to be initialized by referring this point on every axis.

• Work Zero - This is the origin for the measuring of dimensions of workpiece. The programmer is free to select it anywhere on the drawing.

Absolute measuring system - In this measuring system all the dimensions are made from the work zero, which defined. The machine control uses work zero as the reference point to position the tool during program execution. The main advantage of programming in absolute system is that any point can be readily changed without affecting subsequent dimensions.

• Incremental measuring system - The movements are based on the change in position between two successive points. It expresses the relative distance between the current location and the next position. This type of measuring system is called Incremental Measuring system. The main advantage of this system is that sum of the dimensions must always be zero if start point and finishing point is same at the end of programming which makes it easy to check a program.

• Axis designation (conventions) - Axis designation for each type of machine tool is suggested in the EIA (Electronic Industries Association) RS 274-B standard. This conforms to ISO Recommendations R831. The nomenclature of the three main axes (X, Y AND Z) is based on the “Left hand rule”. The thumb indicates the orientation of the X-axis; the index finger indicates the Y-Axis, and the middle finger points in the direction of the Z-axis.

Tool and tool offset - The T function is used to call the particular tool and tool offset in the program. The tool offset is used to correct the values entered in the coordinate system preset block. Using the tool offsets, it is easy to set up the tools and to make adjustments in part size.

• Spindle speed - The spindle speed is the rotational frequency of the spindle of the machine, measured in revolutions per minute (RPM). The preferred speed is determined based on the material being cut. Using the correct spindle speed for the material and tools will greatly affect tool life and the quality of the surface finish.

Feed rate - Feed rate is the velocity at which the cutter is fed, that is, advanced against the workpiece. It is expressed in units of distance per revolution for turning and boring (millimeters per revolution). For milling it is expressed in units of distance per time for milling (millimeters per minute).

Cutting Speed - Cutting speed may be defined as the rate (or speed) that the material moves past the cutting edge of the tool , irrespective of the machining operation used — the surface speed.

S.no.S.no. Process Process no.no.

Tool Tool descriptiondescription

Tool lengthTool length Tool radiusTool radius Tool Tool materialmaterial

Tool insert Tool insert specificationspecification

• Tool Chart -

S.no.S.no. Process Process no.no.

processprocess M/CM/C timetime tooltool remarkremark

• Process Chart -

The construction of CNC machines

1. Elements of motion transmission

• Ball-screws and nut assembly

In a CNC machine, the connection between the screw and the nut is through an endless stream of re-circulating steel balls, replacing sliding friction threads with rolling friction. Advantages are higher efficiency, reversibility and reduction in wear and tear. Hydrostatic slidewaysIn the hydrostatic slideways air or oil is pumped into small pockets machined into slides which are in contact with the slideway.

2. ComputersCNC machines use an on-board computer that allows the operator to read, analyze, and edit programmed information. In CNC machine, computer works on a binary principle, 0 for information and 1 for processing. Special built-in software compiles the user entered program (in code language) into machine language and the machine moves the tool by its servomotors.

3. Control systems

There are two types of control systems on CNC machines: • Open loop (less accurate)• Closed loop (more accurate)The open loop control system does not provide positioning feedback to the control

unit. Since this control system only counts tool movement pulses and cannot identify discrepancies in positioning, it is slightly inaccurate.

In closed loop control system, the electronic movement pulses are sent from the control to the servomotor, enabling the motor movement. Movements are detected by a feedback device (transducer), which can send a signal to the control for checking after each step.

4. Drive motors

The drive motors control machine slide movement on CNC equipment. Types used :1. Stepper motors (convert a digital pulse into a small rotation, mostly used in

applications where low torque is required )2. DC servo motors (rotate in response to the applied voltage, used to drive lead

screw and gear mechanisms, provide higher-torque output)

5. Tool changers

Several different cutting tools are used to produce a part. The tools must be replaced quickly for the next machining operation. For this reason, the majority of NC/CNC machine tools are equipped with automatic tool changers. They allow tool changing without the intervention of the operator. An automatic tool changer grips the tool in the spindle, pulls it out, and replaces it with another tool. Tool changers are equipped for either random or sequential selection. In random tool selection there is no specific pattern of tool selection. In sequential tool selection, the tools must be loaded in the exact order in which they are called for in the program.

3. AC servo motors (controlled by varying the voltage frequency to control speed, more power than a DC servo, used to drive a lead screw and gear mechanism )

4. Fluid servo motors (variable speed motors, produce more power, in the case of pneumatic motors, than electric servomotors)

WORKING OF CNC MACHINES

1. Modes of Operation1. Modes of Operation

Automatic operationAutomatic operation

1. Memory operation1. Memory operation – The required program is already registered in the – The required program is already registered in the CNC memory. We can just select the program and start the operations CNC memory. We can just select the program and start the operations

2. MDI Operation2. MDI Operation - - In the MDI mode, program can be inputted in same In the MDI mode, program can be inputted in same format as normal programs and executed from the MDI panel. Mostly format as normal programs and executed from the MDI panel. Mostly used for simple test operation.used for simple test operation.

3. Program restart3. Program restart - Restarting of a program for automatic operation from - Restarting of a program for automatic operation from an intermediate point, a Sequence No. is assigned to a block. MDI also an intermediate point, a Sequence No. is assigned to a block. MDI also usable as High Speed Program Check Function.usable as High Speed Program Check Function.

4. Manual handle interruption4. Manual handle interruption - Movement by manual handle operation - Movement by manual handle operation can be done by overlapping it with the movement by automatic can be done by overlapping it with the movement by automatic operationoperation

5. Sequence number search - 5. Sequence number search - Function is used to search for a sequence Function is used to search for a sequence number within a program and to start or rescue the program from the number within a program and to start or rescue the program from the block having that sequence number.block having that sequence number.

• Manual operationManual operation

1. Jog feed 1. Jog feed

In the jog mode, a feed axis and direction selection switch on the machine In the jog mode, a feed axis and direction selection switch on the machine operator’s panel moves the tool along the selected direction. The jog feed operator’s panel moves the tool along the selected direction. The jog feed rate can be adjusted with the jog feed-dial rate.rate can be adjusted with the jog feed-dial rate.

2. Incremental feed2. Incremental feed

In the incremental (STEP) mode, pressing a feed axis and direction In the incremental (STEP) mode, pressing a feed axis and direction selection switch on the machine operator’s panel moves the tool one step selection switch on the machine operator’s panel moves the tool one step along the selected axis in the selected direction. Each step can be 10, 100, along the selected axis in the selected direction. Each step can be 10, 100, 1000 times he least input increment ( minimum distance moved by tool).1000 times he least input increment ( minimum distance moved by tool).

3. Manual handle feed3. Manual handle feed

In the handle mode, rotating the manual pulse generator on the machine In the handle mode, rotating the manual pulse generator on the machine operator’s panel can move the tool. The minimum distance the tool is operator’s panel can move the tool. The minimum distance the tool is moved when the manual pulse generator is rotated by one graduation. moved when the manual pulse generator is rotated by one graduation.

4. Manual absolute on and off4. Manual absolute on and off

When the switch is turned on, the distance the tool is moved by manual When the switch is turned on, the distance the tool is moved by manual operation is added to the current coordinates. operation is added to the current coordinates.

2. Processing of CNC programs2. Processing of CNC programs

1.1. Determination of the sequence of operations required in machining Determination of the sequence of operations required in machining process ( involves examining the shape features of the components to process ( involves examining the shape features of the components to be produced) .be produced) .

2.2. Selection of cutting tools, order of use corresponding to the sequence Selection of cutting tools, order of use corresponding to the sequence of operations and determination of feeds and cutting speeds for each of operations and determination of feeds and cutting speeds for each operation. operation.

3.3. Settings of program auxiliary functions, including tool changes, Settings of program auxiliary functions, including tool changes, spindle starts and stops, coolant on and off and so on. spindle starts and stops, coolant on and off and so on.

3. Analyses of drawing for CNC programming

3.1 STUDY OF DRAWING• Verification of drawing quadrant/angle~ 1st and 3rd

• Unit of measurement: mm and inch• Raw material size• Drawing zero/work piece zero• Marking of all the turning points (where profile is changing) & working points

(for drilling, boring etc.)

• Section of measuring system-Absolute, Incremental • Making of co-ordinates for all turning points and working points.• Study of tolerances and important dimensions.

3.2 PART PROGRAM STRUCTURE 1. Name of the program2. Selection of Working plane, Measuring system ( Absolute or incremental ), unit of measurement (mm or inch)3. Defining and calling work origin4. Tool changing position (Remote area away from work piece), Tool call & Tool change5. First position (Movement in working Plane) and Second positioning (Movement in

spindle axis) for working, Spindle start & coolant on6. Third positioning for working (for mechanizing, tool movement with tool radius

compensation)7. Depth of cut (in feed only)8. Definition of geometry/preparation of profile (feeding of CNC drawing data)9. Return to second position, spindle stop & coolant off10. Cancellation of fixed cycles, Macro instructions, Special commands, Tool Radius

compensation11. Return to tool change position12. Movement in spindle axis and in working plane13. If required, repeat step Nos. to 16 as required.14. End of part program

FUNDAMENTALS OF PROGRAMMINGFUNDAMENTALS OF PROGRAMMING Numerical control machine are programmed by means of a series of coded Numerical control machine are programmed by means of a series of coded

instructions, commonly entered into the controller using manual programming. instructions, commonly entered into the controller using manual programming. Each set of instruction codes that machine acts upon is called NC block and is Each set of instruction codes that machine acts upon is called NC block and is terminated on the program by means of an end character (EOB) that corresponds terminated on the program by means of an end character (EOB) that corresponds

to the carriage return. A typical block of instruction is of the following form:to the carriage return. A typical block of instruction is of the following form:

N001 G80 X75 Y65 Z10 F60 S160 T01M03 EOBN001 G80 X75 Y65 Z10 F60 S160 T01M03 EOB

CODE TYPESCODE TYPES

Sequence Number (N-Codes)Sequence Number (N-Codes)This is an identification number for each block of instructions and increases This is an identification number for each block of instructions and increases

sequentially through the program.sequentially through the program.

Preparatory Function (G-Codes)Preparatory Function (G-Codes)The G-codes are the codes that position the tool and do the actual workThe G-codes are the codes that position the tool and do the actual work . These . These

codes are largely standardized and can be seen in the provided G-code table. codes are largely standardized and can be seen in the provided G-code table. Many of the preparatory functions can indicate canned cycles.Many of the preparatory functions can indicate canned cycles.

Co-ordinate codesThese indicate the co-ordinates for the tool movement. Four to five axis machines can have the following axes.

Cartesian Co-ordinatesCartesian Co-ordinates Angular positions for the Angular positions for the Cartesian axesCartesian axes

Circular Interpolation Circular Interpolation about Cartesian axesabout Cartesian axes

XX AA II

YY BB JJ

ZZ CC KK

Feed rate (F-code)This specifies the feed rate for the operation. The units may be mm per minute or mm per revolution (indicated by the G-code used), with the decimal point implied at a fixed position from the right.

Spindle speed (s-code)This specifies the spindle speed to be used for the operation.

Tool NumberThis indicates to the controller which tool is to be used for the operation. In case of tool adaptors with multiple tool slots, the machine just switches to the next tool without removing the earlier one form the adaptor.

Miscellaneous Code (M-code)These codes program various auxiliary functions on the machine tool. The miscellaneous function may be acted upon at the start or the end of the motion described by a block of instruction. With word address format, information need not be repeated in successive blocks if it is to remain the same for subsequent blocks.

ISO MISCELLANEOUS FUNCTIONS ( M-Codes ) CODE FUNCTIONM00 Program stop, spindle and coolant offM01 Optional programmable stopM02 End of program-often interchangeable with M30M04 Spindle on CCWM05 Spindle stopM06 Tool changeM07 Coolant supply No. 1 onM08 Coolant supply No. 2 onM09 Coolant offM10 ClampM11 UnclampM13 Spindle on, CW + Coolant on

M14 Spindle on, CCW + Coolant onM 20 – 29 Unassigned M30 Program stops at end of tape+ tape rewindM31 Interlock by-passM40-M45 Gear Changes; otherwise unassignedM90 Reserved for userM99 (Subroutine call) Reserved for user

G - Codes(Fanuc Machine Control) G CODE FUNCTIONG00 Positioning (Rapid traverse)G01 Linear Interpolation (Cutting feed)G02 Circular interpolation /Helical cutting CWG03 Circular interpolation/Helical cutting CCWG04 Dwell TimeG17 XY plane selectionG18 ZX plane selectionG19 YZ plane selectionG20- 21 Input in inch and mm respectively.

G28 Return to reference pointG40 Cutter compensation cancelG41 Cutter compensation leftG42 Cutter compensation rightG43 Tool length compensation + directionG44 Tool length compensation – directionG53 Machine coordinates system selectionG54 - 59 Work co-ordinate system 1 -6 selectionG80 Canned cycle cancelG81 Drilling cycle, spot boringG82 Drilling cycle, counter boringG83 Peck drilling cycleG84 Tapping cycleG85 Rough Boring cycleG86 Finish Boring cycleG90 Absolute commandG91 Incremental commandG92 Programming of absolute zero pointG94/98 Feed per minuteG95/99 Feed per rotationG96 Constant surface speed control

G97 Constant surface speed controls cancelG98 Return to initial point in canned cycleG99 Return to R point in canned cycle

Sample Code G00 X 5.0 Y 5.0 ;Here we rapid tool movement to co-ordinates (5,5). “Air cutting” is minimized by G00 and tool need move along a straight line only.

Tool at start position

Program Zero

5.0

5.0

G41(Radius compensation on the left side of the profile)

G42(Radius compensation on the right side of the profile)

Fixed or canned cyclesMany NC machines can be programmed using fixed or canned cycles.

• Drilling Cycle, Spot drilling (G81)This cycle, is used for normal drilling. Drilling is performed at cutting feed to the bottom of the hole. The tool is then retracted from the bottom of the hole to retraction height in rapid traverse.G81 X_ Y_ Z_ R_ F_ K_ ;

• Drilling Cycle, counter boring drilling (G82)This cycle, is used for counter boring, similar to G81. At the bottom, a dwell is performed, then tool retraction takes place. More accurate drilling w.r.t depth.G82 X_ Y_ Z_ R_ P_ F_ K_ ;

• Peck drilling Cycle (G83)This cycle performs peck drilling. Drilling is performed at intermittent cutting feed to the bottom of hole while removing chips from the hole. G83_ X_ Y_ Z_ R_ Q_ F_ K_ ; Tapping cycle (G84)This cycle is used for tapping. Spindle rotated clockwise, when the bottom of the hole reached the spindle is rotated in the reverse direction for retraction. G84_ X_ Y_ Z_ R_ F_ K_;

Rough Boring cycle (G85)This cycle, is used to bore a hole. G85 X_ Y_ Z_ R_ F_ K_ ;

Finish Boring cycle (G86)This cycle, is used to bore a hole, a better surface finish is obtained.G86 X_ Y_ Z_ R_ F_ K_ ;

In all of the above canned cycles, the following parameters need to be providedX_ Y_ : Hole position dataZ_ : The distance from point R to bottom of the holeR_ : The distance from the initial level to point R levelF_ : Cutting feed rateK_ : Number of repeats

Multiple repetitive Cycles• Stock Removal in Facing (G71) G71 U(Δd) R(e) G71 P(Ns) Q(Nf) U(Δu) W(Δw) F(t) S(s) T(t) ;

Stock Removal in Facing (G72)Stock Removal in Facing (G72) G72 W(Δd) R(e)G72 W(Δd) R(e) G72 P(Ns) Q(Nf) U(Δu) W(Δw) F(t) S(s) T(t) ;G72 P(Ns) Q(Nf) U(Δu) W(Δw) F(t) S(s) T(t) ; Cutting is made by operation parallel to Z-axis.Cutting is made by operation parallel to Z-axis.

Stock Removal in Facing (G73)Stock Removal in Facing (G73) This function permits cutting a fixed pattern repeatedly.This function permits cutting a fixed pattern repeatedly. G73 U(Δi) W(Δk) R(d)G73 U(Δi) W(Δk) R(d) G73 P(Ns) Q(Nf) U(Δu) W(Δw) F(t) S(s) T(t) ;G73 P(Ns) Q(Nf) U(Δu) W(Δw) F(t) S(s) T(t) ;

Finishing Cycle (G70)Finishing Cycle (G70) G70 P(Ns) Q(Nf) U(Δu) W(Δw)G70 P(Ns) Q(Nf) U(Δu) W(Δw) ; ;

In all the above cycles,In all the above cycles,ΔdΔd : depth of cut (radius designation) (designation without sign) in x direction : depth of cut (radius designation) (designation without sign) in x directionee : escaping amount/retraction : escaping amount/retractionNsNs : sequence number of first block for programming of finishing shape : sequence number of first block for programming of finishing shapeNfNf : sequence number of last block for programming of finishing shape : sequence number of last block for programming of finishing shapeΔu Δu : distance and direction of finishing allowance in X direction (dia/radius) : distance and direction of finishing allowance in X direction (dia/radius)ww : distance and direction of finishing allowance in Z direction : distance and direction of finishing allowance in Z direction F, S, TF, S, T : Any F, S, T function contained on block Ns to Nf in the cycle is ignored : Any F, S, T function contained on block Ns to Nf in the cycle is ignored and the F, S, T function in this G71 block is effective.and the F, S, T function in this G71 block is effective.

The importance of lathes and milling machines even if they are conventional cannot be undermined. These machines have played a real important role in bringing about industrial revolution and have laid the foundations. But the bringing about of the new technology in the present era is very important. The conventional machines are required in small quantities whereas the CNC machines must be increased to improve the quantity and quality of production.

CONCLUSIONCONCLUSION

Points of difference b/w CNC and Conventional Points of difference b/w CNC and Conventional MachinesMachines

CNC Machine Conventional Machine

CNC machines can be used continuously for long intervals and only need to be switched off for occasional maintenance.

Conventional machines are difficult operate for several hours at a stretch. The operator has to continuously focus on the job at hand.

CNC machines can produce several products, all similar and dead accurate

Resemblance of the products formed depends on the skill of the operator. Visible differences may occur

Less skilled/trained persons can operate the CNC machines.

Highly skilled operators are required to work on conventional machines

CNC machines can be updated by using improved software to drive the machines.

Chances for major improvement in the same conventional machines are very less.

One person can supervise several CNC machines, and they can be left to work themselves.

One person cannot operate more than one conventional machine at a time

REFERENCES1. www.nplindia.org2. www.wikpedia.org 3. www.fortune.com4. www.headland.com5. www.machinetoolhelp.com6. www.cncezpro.com7. I.C.GROVER, “CAD/CAM”, published by Macmillon8. NARANG, “Introduction to Numerical Control”9. P.S.GILL and KRAR, “Fundamental of Numeric Control”10.STEVE KRAR & ARTHUR GILL, “CNC Technology and

Programming”, published by McGraw Hill11.Members of the Mechanical Workshop, National Physical

Laboratory, New Delhi