19647980 cnc machine tools

7/30/2019 19647980 Cnc Machine Tools

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CNC TECHNOLOGYand

CNC PROGRAMMING

ME 445INTEGRATED MANUFACTURING SYSTEMS


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AUTOMATION IN MANUFACTURINGSYSTEMS

TRENDS IN INDUSTRY

THE OBJECTIVE:

TO BE COMPETITIV THROUGH INCREASING PRODUCTIVITY AND TOTAL QUALITY ASSURANCE


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EFFICIENCY OF

MANUFACTURING

COST = COST OF MANUFACTURING AND COST OF MATERIALHANDLING

PROFIT = INCOME - COST

PRODUCTIVITY =AVERAGE OUTPUT PER MAN-HOUR


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PROFIT increases as COST decreases

and as PRODUCTIVITY increases.

PRODUCTIVITY through AUTOMATION


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AUTOMATION

any means of helpingthe workers to performtheir tasks more

efficiently

transfer of the skill of the operator to themachine


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Transferred

skill Results

muscle power engine drivenmachine tools

First industrialrevolution

manipulating

skill

mechanization hard automation

vision skill use of positiontransducers,

cameras

increase of accuracy, part

recognition brain power cnc machines, industrial

robots, soft automation,

computer control of manufacturing

systems

second industrialrevolution


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Utilization of computers inmanufacturing applications hasproved to be one of the most

significant developments over thelast couple of decades in helping toimprove the productivity andefficiency of manufacturing

systems.


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The metal cutting operations (also called machining) is one of themost important manufacturing

processes in industry today (as it

was yesterday) .


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MACHINING IS THE REMOVAL OF MATERIALS IN FORMS OF CHIPS FROM THE WORKPIECE BY SHEARING WITH A SHARP

TOOL.


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The main function of a machinetool is to control the workpiece-

cutting tool positional relationshipin such a way as to achieve a

desired geometric shape of the

workpiece with sufficientdimensional accuracy.


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Machine tool provides:

work holdingtool holdingrelative motion between tooland workpiece

primary motion secondary motion


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Primary motion

Relative motionbetween tool and

workpiece

Secondary motion

Cutting motion

Cutting speed

Feed motion

Feed rate


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m a c h i n e c o n t r o l u n i t

p o s i t i o n t r a n s d u c e r s

w o r k h o l d i n g d e v i c e

t o o l h o l d i n g d e v i c e


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CLASSIFICATION OF THE CHIP REMOVING METHODS ACCORDING TO THE RELATIVE MOTION


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CLASSIFICATION OF MACHINE TOOLS

THOSE USINGSINGLE POINTTOOLS

THOSE USINGMULTIPOINTTOOLS

THOSE USINGABRASIVETOOLS

lathesshapersplaners

boring m/cs etc.

drilling m/cs milling m/cs

broaching m/cs hobbing m/cs etc.

grinding m/cs honing m/cs etc.


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ISO MACHINE TOOL AXIS DEFINITION


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ISO MACHINE TOOL AXES DEFINITIONS

AXIS MACHINE TOOL WITH SPINDLE MACHINE TOOL WITH NO SPINDLE

Z axis of spindle,(+Z) as tool goes away from the work piece

perpendicular to work holding surface, (+Z) astool goes away from theworkpiece

MACHINE TOOL WITH

ROTATINGWORKPIECE

MACHINE TOOL WITH ROTATING TOOL

HORIZONT AL AXIS

VERTICAL AXIS

X radial andparallel tocross slide,(+X) whentool goes awayfrom the axis

of spindle

horizontaland parallelto work holdingsurface,(+X) to the

right whenviewedfromspindletowardswork piece

horizontaland parallelto the work holdingsurface,(+X) to the

right whenviewedfromspindletowardscolumn

parallel to and positive inthe principal direction of cutting (primary motion)

Y apply right hand rules


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RIGHT HAND RULE Vertical Machine Horizontal Machine


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STANDARD LATHE COORDINATE

SYSTEM


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STANDARD MILLING MACHINE

COORDINATE SYSTEM


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NUMERICALLY CONTROLLED MACHINE

TOOLS: An NC machine tool is functionally the sameas a conventional machine tool. The

technological capabilities NC machine toolsin terms of machining are no different fromthose of conventional ones. The differenceis in the way in which the various machine

functions and slide movements arecontrolled.


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The functions and motions such as;

turning the spindle on and off setting cutting speeds setting feed rate turning coolant on and off moving tool with respect to workpiece

are performed by Machine Control Unit(MCU) in NC machine tools.


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INTRODUCTION TO CNC


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HISTORY

US Air Force commissioned MIT to develop thefirst "numerically controlled" machine in 1949. It

was demonstrated in 1952.At 1970-1972 first Computer Numeric Control

machines were developed.Today, computer numerical control (CNC)machines are found almost everywhere, fromsmall job shops in rural communities tocompanies in large urban areas.


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DEFINITION

In CNC (Computer Numerical Control), theinstructions are stored as a program in a

micro-computer attached to the machine.The computer will also handle much of thecontrol logic of the machine, making it

more adaptable than earlier hard-wiredcontrollers.


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CNC APPLICATIONS Machining2.5D / 3DTurning ~ Lathes, Turning Centre

Milling ~ Machining CentresForming2D

Plasma and Laser CuttingBlanking, nibbling and punching3DRapid Prototyping


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SAMPLECNC MACHINES


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CNC TURNING


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CNC MILLING


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CNC LASER CUTTING


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CNC PLASMA CUTTING


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CNC PRESS


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CNC RAPID PROTOTYPING


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INDUSTRIES MOST AFFECTEDby CNC

AerospaceMachineryElectricalFabrication

AutomotiveInstrumentationMold making


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SAMPLE PRODUCTS

OFCNC MANUFACTURING


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AUTOMOTIVE INDUSTRY

Engine Block


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AUTOMOTIVE INDUSTRY(Contd)

Different Products


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AEROSPACE INDUSTRY Aircraft Turbine Machined by

5-Axis CNC Milling Machine


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CNC MOLD MAKING


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ELECTRONIC INDUSTRY


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RAPID PROTOTYPINGPRODUCTS


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ADVANTAGES of CNC

ProductivityMachine utilisation is increased becausemore time is spent cutting and less time istaken by positioning.Reduced setup time increases utilisationtoo.


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ADVANTAGES of CNC

QualityParts are more accurate.Parts are more repeatable.Less waste due to scrap.


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ADVANTAGES of CNC

Reduced inventoryReduced setup time permits smallereconomic batch quantities.Lower lead time allows lower stock levels.Lower stock levels reduce interest chargesand working capital requirements.


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ADVANTAGES of CNC

Machining Complex shapesSlide movements under computer control.Computer controller can calculate steps.First NC machine built 1951 at MIT foraircraft skin milling.


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ADVANTAGES of CNC

Management ControlCNC leads to CADProcess planningProduction planning


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DRAWBACKS of CNCHigh capital cost

Machine tools cost $30,000 - $1,500,000Retraining and recruitment of staff New support facilitiesHigh maintenance requirementsNot cost-effective for low-level production onsimple parts

As geometric complexity or volume increasesCNC becomes more economical

Maintenance personnel must have bothmechanical and electronics expertise


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CNC SYSTEM ELEMENTS


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CNC SYSTEM ELEMENTS

A typical CNC system consists of thefollowing six elementsPart program

Program input deviceMachine control unitDrive system

Machine toolFeedback system


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NC SYSTEM ELEMENTS


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OPERATIONAL FEATURES of CNCMACHINES


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PART PROGRAM A part program is a series of coded instructions requiredto produce a part. It controls the movement of themachine tool and the on/off control of auxiliary functionssuch as spindle rotation and coolant. The codedinstructions are composed of letters, numbers andsymbols and are arranged in a format of functionalblocks as in the following example

N10 G01 X5.0 Y2.5 F15.0 | | | | || | | | Feed rate (15 in/min)

| | | Y-coordinate (2.5")| | X-coordinate (5.0")| Linear interpolation mode

Sequence number


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PROGRAM INPUT DEVICE

The program input device is themechanism for part programs to be

entered into the CNC control. The mostcommonly used program input devices arekeyboards, punched tape reader, diskette

drivers, throgh RS 232 serial ports andnetworks.


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MACHINE CONTROL UNITThe machine control unit (MCU) is the heart of a CNCsystem. It is used to perform the following functions:

Read coded instructionsDecode coded instructions

Implement interpolations (linear, circular, and helical) togenerate axis motion commandsFeed axis motion commands to the amplifier circuits fordriving the axis mechanisms

Receive the feedback signals of position and speed foreach drive axisImplement auxiliary control functions such as coolant orspindle on/off, and tool change


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TYPES of CNC CONTROLSYSTEMS

Open-loop controlClosed-loop control


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OPEN-LOOP CONTROL SYSTEM

In open-loop control system step motors areusedStep motors are driven by electric pulsesEvery pulse rotates the motor spindle through acertain amountBy counting the pulses, the amount of motion

can be controlledNo feedback signal for error correctionLower positioning accuracy


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CLOSED-LOOP CONTROL

SYSTEMSIn closed-loop control systems DC or ACmotors are used

Position transducers are used to generateposition feedback signals for errorcorrectionBetter accuracy can be achievedMore expensiveSuitable for large size machine tools


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DRIVE SYSTEM

A drive system consists of amplifiercircuits, stepping motors or servomotors

and ball lead-screws. The MCU feedscontrol signals (position and speed) of each axis to the amplifier circuits. Thecontrol signals are augmented to actuate

stepping motors which in turn rotate theball lead-screws to position the machinetable.


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STEPPING MOTORS

A stepping motor provides open-loop, digitalcontrol of the position of a workpiece in anumerical control machine. The drive unitreceives a direction input (cw or ccw) and pulse

inputs. For each pulse it receives, the drive unitmanipulates the motor voltage and current,causing the motor shaft to rotate bya fixed angle(one step). The lead screw converts the rotarymotion of the motor shaft into linear motion of the workpiece .


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STEPPING MOTORS


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RECIRCULATING BALL SCREWS

Transform rotational motion of the motorinto translational motion of the nut attached tothe machine table.


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RECIRCULATING BALL SCREWS

Accuracy of CNCmachines depends ontheir rigidconstruction, care inmanufacturing, andthe use of ball screwsto almost eliminate

slop in the screwsused to move portionsof the machine.


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POSITIONING

The positioning resolution of a ball screw drivemechanism is directly proportional to thesmallest angle that the motor can turn.The smallest angle is controlled by the motorstep size.Microsteps can be used to decrease the motorstep size.CNC machines typically have resolutions of 0.0025 mm or better.


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MACHINE TOOL

CNC controls are used to control varioustypes of machine tools. Regardless of

which type of machine tool is controlled, italways has a slide table and a spindle tocontrol of position and speed. The

machine table is controlled in the X and Y axes, while the spindle runs along the Zaxis.


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FEEDBACK SYSTEM

The feedback system is also referred to asthe measuring system. It uses position

and speed transducers to continuouslymonitor the position at which the cuttingtool is located at any particular time. TheMCU uses the difference between

reference signals and feedback signals togenerate the control signals for correctingposition and speed errors.


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CNC MACHINES FEEDBACK

DEVICES


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POTENTIOMETERS


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POTENTIOMETERS

ENCODERS


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ENCODERS

A device used to convert linear or

rotational position information into anelectrical output signal.


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ENCODERS


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INDUSTRIAL APPLICATIONS of ENCODERS


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RESOLVERS

A resolver is a rotarytransformer that

produces an output signalthat is a function of therotor position.


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SERVOMOTOR with RESOLVER


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VELOCITY FEEDBACK

Tachometers:Electrical output is proportional to rate of angular rotation.

Encoders, Resolvers, Potentiometers:Number of pulses per time is proportionalto rate change of position.


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CNC CUTTERS

Turning center cuttersMachining center cutters


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TURNING CENTER CUTTERS

Types of cutters used on CNC turningcenters

Carbides (and other hard materials) insertturning and boring toolsCeramics

High Speed Steel (HSS) drills and taps


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STANDART INSERT SHAPES V used for profiling, weakestinsert, 2 edges per side.D somewhat stronger, used forprofiling when the angle allows it,2 edges per side.T commonly used for turningbecause it has 3 edges per side.C popular insert because thesame holder can be used forturning and facing. 2 edges perside.W newest shape. Can turn andface like the C, but 3 edges perside.S Very strong, but mostly usedfor chamfering because it wontcut a square shoulder. 4 edgesper side.R strongest insert but leastcommonly used.

TYPICAL TURNING,


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TYPICAL TURNING,THREADING and PARTING TOOLS

MACHINING CENTER CUTTING


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MACHINING CENTER CUTTINGTOOLS

Most machining centersuse some form of HSS orcarbide insert endmill as

the basic cutting tool.Insert endmills cut manytimes faster than HSS,but the

HSS endmills leave abetter finish when sidecutting.



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MACHINING CENTER CUTTINGTOOLS (contd)

Facemills flatten largesurfaces quickly andwith an excellentfinish. Notice theengine block beingfinished in one pass

with a large cutter.



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Ball endmills (bothHSS and insert) areused for a variety of profiling operationssuch as the moldshown in the picture.Slitting and sidecutters are used whendeep, narrow slotsmust be cut.



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Drills, Taps, and ReamersCommon HSS tools such asdrills, taps, and reamers arecommonly used on CNC

machining centers. Note that aspot drill is used instead of acenterdrill. Also, spiral point orgun taps are used for throughholes and spiral flute for blindholes. Rarely are hand tapsused on a machining center.

TOOL HOLDERS


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TOOL HOLDERS

All cutting tools must be held in a holderthat fits in the spindle. These include endmill holders (shown), collet holders, facemill adapters, etc. Most machines in theUSA use a CAT taper which is a modifiedNST 30, 40, or 50 taper that uses a pullstud and a groove in the flange. Themachine pulls on the pull stud to hold theholder in the spindle, and the groove inthe flange gives the automatic toolchanger something to hold onto. HSK toolholders were designed a number of yearsago as an improvement to CAT tapers,but they are gaining acceptance slowly.


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CNC PROGRAMMING


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CNC PROGRAMMING

Offline programming linked to CAD programs.Conversational programming by the

operator.MDI ~ Manual Data Input.Manual Control using jog buttons or`electronic handwheel'.Word-Address Coding using standard G-codesand M-codes.


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During secondary motion, either the tool

moves relative to the workpiece or theworkpiece moves relative to the tool. In NCprogramming, it is always assumed that the

tool moves relative to the workpiece nomatter what the real situation is.

Basics of NC Part Programming:


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The position of the tool is describedby using a Cartesian coordinate

system. If (0,0,0) position can bedescribed by the operator, then it is

called floating zero .


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In defining the motion of the toolfrom one point to another,eitherabsolute positioning mode orincremental positioning mode

can be used.


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1. Absolute positioning . In this mode, thedesired target position of the tool for aparticular move is given relative to the origin

point of the program.

2. Incremental positioning . In this mode,the next target position for the tool is givenrelative to the current tool position.


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Structure of an NC Part Program:

Commands are input into the controller inunits called blocks or statements .

Block Format:

1. Fixed sequential format

2. Tab sequential format3. Word address format

EXAMPLE:


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EXAMPLE: Assume that a drilling operation is to be

programmed as:

1. The tool is positioned at (25.4,12.5,0) by a

rapid movement.2. The tool is then advanced -10 mm in the zdirection at a feed rate of 500 mm/min., with theflood coolant on.

3.The is then retracted back 10 mm at the rapidfeed rate, and the coolant is turned off.


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1. Fixed sequential format0050 00 +0025400 +0012500 +0000000 0000 000060 01 +0025400 +0012500 -0010000 0500 080070 00 +0025400 +0012500 +0000000 0000 09

2. Tab sequential format0050 TAB 00 TAB +0025400 TAB +0012500 TAB +0000000 TAB TAB0060 TAB 01 TAB TAB TAB -0010000 TAB 0500 TAB 080070 TAB 00 TAB TAB TAB -0000000 TAB 0000 TAB 09

3. Word address formatN50 G00 X25400 Y125 Z0 F0N60 G01 Z-10000 F500 M08N70 G00 Z0 M09

M d l d : Commands iss ed in the


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Modal commands : Commands issued in theNC program that will stay in effect until it ischanged by some other command, like, feedrate selection, coolant selection, etc.

Nonmodal commands : Commands that areeffective only when issued and whoseeffects are lost for subsequent commands,like, a dwell command which instructs thetool to remain in a given configuration for agiven amount of time.


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CNC PROGRAMMING


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INFORMATION NEEDED by a CNC

1. Preparatory Information: units, incremental or absolutepositioning

2. Coordinates: X,Y,Z, RX,RY,RZ3. Machining Parameters: Feed rate and spindle speed4. Coolant Control: On/Off, Flood, Mist5. Tool Control: Tool and tool parameters6. Cycle Functions: Type of action required7. Miscellaneous Control: Spindle on/off, direction of

rotation, stops for part movementThis information is conveyed to the machine through a setof instructions arranged in a desired sequence Program.

BLOCK FORMAT


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Sample Block N135 G01 X1.0 Y1.0 Z0.125 F5

Restrictions on CNC blocksEach may contain only one tool moveEach may contain any number of non-tool move G-codesEach may contain only one feedrateEach may contain only one specified tool or spindlespeed

The block numbers should be sequentialBoth the program start flag and the program numbermust be independent of all other commands (onseparate lines)The data within a block should follow the sequenceshown in the above sample block


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WORD-ADDRESS CODING

N5 G90 G20N10 M06 T3N15 M03 S1250N20 G00 X1 Y1N25 Z0.1N30 G01 Z-0.125 F5N35 X3 Y2 F10

N40 G00 Z1N45 X0 Y0N50 M05N55 M30

Example CNC Program Each instruction to the machineconsists of a letter followed by anumber.

Each letter is associated with aspecific type of action or piece of information needed by the machine.

Letters used in Codes

N,G,X,Y,Z,A,B,C,I,J,K,F,S,T,R,M


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G & M Codes

N5 G90 G20N10 M06 T3N15 M03 S1250N20 G00 X1 Y1N25 Z0.1N30 G01 Z-0.125 F5N35 X3 Y2 F10

N40 G00 Z1N45 X0 Y0N50 M05N55 M30

Example CNC Program G-codes : Preparatory Functions

involve actual tool moves.

M-codes : MiscellaneousFunctions involve actionsnecessary for machining (i.e.spindle on/off, coolant on/off).


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G CodesG00 Rapid traverseG01 Linear interpolationG02 Circular interpolation,

CWG03 Circular interpolation,

CCWG04 DwellG08 AccelerationG09 DecelerationG17 X-Y PlaneG18 Z-X PlaneG19 Y-Z PlaneG20 Inch Units (G70)G21 Metric Units (G71)

G40 Cutter compensation cancel

G41 Cutter compensation left

G42 Cutter compensation-rightG70 Inch formatG71 Metric formatG74 Full-circle programming

off G75 Full-circle programming

onG80 Fixed-cycle cancelG81-G89 Fixed cyclesG90 Absolute dimensions

G91 Incremental dimensions


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Modal G-Codes

Most G-codes set the machine in a mode which stays in effect until it is changed orcancelled by another G-code. These

commands are called modal.


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Modal G-Code ListG00 Rapid TransverseG01 Linear InterpolationG02 Circular Interpolation, CWG03 Circular Interpolation,

CCWG17 XY PlaneG18 XZ PlaneG19 YZ PlaneG20/G70 Inch unitsG21/G71 Metric UnitsG40 Cutter compensation

cancel

G41 Cutter compensation leftG42 Cutter compensation rightG43 Tool length compensation

(plus)

G43 Tool length compensation(plus)

G44 Tool length compensation(minus)

G49 Tool length compensationcancel

G80 Cancel canned cyclesG81 Drilling cycleG82 Counter boring cycleG83 Deep hole drilling cycleG90 Absolute positioningG91 Incremental positioning


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M CodesM00 Program stopM01 Optional program stopM02 Program endM03 Spindle on clockwise

M04 Spindle on counterclockwiseM05 Spindle stopM06 Tool changeM08 Coolant onM09 Coolant off M10 Clamps onM11 Clamps off M30 Program stop, reset to start


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N Codes

Gives an identifying number for each block of information.

It is generally good practice to incrementeach block number by 5 or 10 to allow

additional blocks to be inserted if futurechanges are required.


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X,Y, and Z Codes

X, Y, and Z codes are used to specify thecoordinate axis.

Number following the code defines thecoordinate at the end of the move relativeto an incremental or absolute reference

point.


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I,J, and K Codes

I, J, and K codes are used to specify thecoordinate axis when defining the center

of a circle.

Number following the code defines the

respective coordinate for the center of thecircle.


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F,S, and T Codes

F-code : used to specify the feed rate

S-code : used to specify the spindle speed

T-code : used to specify the toolidentification number associated with thetool to be used in subsequent operations.

Application of Some Codes


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Application of Some CodesG01 Linear Interpolation

Format: N_ G01 X_ Y_ Z_ F_

Linear Interpolation results in a straightline feed move.

Unless tool compensation is used, thecoordinates are associated with thecenterline of the tool.



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. As an example, for the motion that occurs inx-y plane with the same maximum speed for thex- and y-axis, initial motion is at an angle of 45oto the axes until motion in one of

the axes is completed and then the balance of

the motion occurs in the other axis. This is calledpoint-to-point motion .



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5

1 0

1 5

2 0

2 5

5 1 0 1 5 2 0 2 5 3 0

A

B C

P o s i t i o n i n g m o t i o n f r o m A t o C

N 1 0 G 0 0 X 3 0 0 0 0 Y 2 0 0 0 0 F 0



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G01 is another preparatory function to specifythat the tool should be moved to a specifiedlocation along a straight line path. It is referredto as linear interpolation .

This function is typically used to specifymachining of straight features such as turninga cylindrical surface in turning, cutting a slot inmilling, etc.



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5

1 0

1 5

2 0

2 5

5 1 0 1 5 2 0 2 5 3 0

A

C

L i n e a r i n t e r p o l a t i o n f r o m A t o C

N 1 0 G 0 1 X 3 0 0 0 0 Y 2 0 0 0 0 F 2 5 0 0

G01 Linear Interpolation


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N10 G00 X1 Z1N15 Z0.1N20 G01 Z-0.125 F5N25 X2 Z2 F10

G01 Linear Interpolation

X

Z

G02 Ci l I l i


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G02 Circular Interpolation

G02 is also a preparatory function to specify thatthe tool should be moved to a specified locationalong a circular path in a clockwise direction. Inorder to specify the path to the MCU, the endpoint of the arc and the location of the center of the arc should be specified. Within the block inwhich the G02 code is programmed, the centerof the arc is given by specifying its locationrelative to the start of the arc.

G02 Ci l I l i (CW)


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G02 Circular Interpolation (CW)

The G02 command requires anendpoint and a radius in orderto cut the arc.I,J, and K are relative to thestart point.

N_ G02 X2 Y1 I0 J-1 F10

orN_ G02 X2 Y1 R1

G02 Ci l I l i (CW)


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G02 Circular Interpolation (CW)

5

1 0

1 5

2 0

2 5

5 1 0 1 5 2 0 2 5 3 0

C

C

C i r c u l a r i n t e r p o l a t i o n f r o m A t o B

a b o u t a c i r c l e c e n t e r e d a t C

N 1 0 G 0 2 X 2 0 0 0 0 Y 1 0 0 0 0

I 5 0 0 0 J 1 5 0 0 0 F 2 5 0 0

A

B

I = 5

J = 1 5

Canned Cycles


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Some Commonly Used Canned Cycle


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Code Function Down feed At bottom Retracti on

G81 Drilling Continuousfeed

No action Rapid

G82 Spot face,counterbore

Continuousfeed

Dwell Rapid

G83 Deep hole drilling Peck No action Rapid

G84 Tapping Continuousfeed

Reversespindle

Feedrate

G85 Through boring(in& out) Continuousfeed No action Feedrate G86 Through boring(in

only) Continuous

feed Stop

spindle Rapid

G81 ILLUSTRATION


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Th M i t f CNC


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Three Main parts of a CNC program

N5 G90 G21 (Absolute units, metric)

N10 M06 T2 (Stop for tool change, use

tool # 2)N15 M03 S1200 (Turn the spindle on CW to1200 rpm)

Part 1- Program Petup

Th M i t f CNC g


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N20 G00 X1 Y1 (Rapid to X1,Y1 from originpoint)N25 Z0.125 (Rapid down to Z0.125)N30 G01 Z-0.125 F100 (Feed down to Z-0.125 at

100 mm/min)

N35 G01 X2 Y2 (Feed diagonally to X2,Y2)N40 G00 Z1 (Rapid up to Z1)N45 X0 Y0 (Rapid to X0,Y0)

Part 2- Chip Removal

Th M i t f CNC g


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N50 M05 (Turn the spindle off)

N55 M00 (Program stop)

Part 3- System Shutdown

EXAMPLE OPERATION on CNC


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MILLING MACHINE

G CODE PROGRAM


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G-CODE PROGRAM

First pass : conventional mill toa depth of 0.125 around edgeprofile. Tool 1 is a inch dia.end mill.

%:1002N5 G90 G20N10 M06 T1N15 M03 S1200N20 G00 X0.125 Y0.125

N30 Z0.125N35 G01 Z-0.125 F5N40 X3.875N45 Y4.125N50 X0.125N55 Y0.125

Second pass:


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pconventional mill to a

depth of 0.25 aroundedge profile.

N35 Z-0.250N40 X3.875N45 Y4.125N50 X0.125N55 Y0.125N60 Z0.125

Third pass:conventional mill to a


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conventional mill to adepth of 0.125

around pocket profile.

N65 G00 X1.25 Y1.0N70 G01 Z-0.125 F5N75 X1.75N80 Y2.5N85 X1.25

N90 Y1.0N95 Z0.125

Fourth pass: climbill d h f


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mill to a depth of 0.125 acrossremaining material.

N100 Y2.125N105 X2.625N110 Z0.125N115 G00 X-5 Y-5 Z5

N120 M05N125 M30

Advanced features:


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Execution of the part of the program in arotated or mirrored position.

Ability to scale the program and producelarger or smaller programs.Three dimensional circular interpolationwhich produces a helical shape.Parabolic and cubic interpolation.


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Program Loading:

Through keyboard

Through punched tape readerThrough diskette driveThrough RS 232 serial port

Through network interface card

Direct Numerical Control (DNC):


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A system in which a central computerdownloads the NC programs block by block to many NC machine tools simultaneously iscalled Direct Numerical Control (DNC )system.




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This system used to work with the early NCmachine tools which can not read more than ablock of information at a time. The centralcomputer feed the program information oneblock at a time. When the machine execute theinformation, the next block of informationwould be fed.

( )

Distributed Numerical Control (DNC):


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Distributed NC is known by the same acronymas Direct Numerical Control (DNC). After theintroduction of CNC, the machine tools havehad the capability of storing large amount of

information. Therefore, there have been noneed to have drip feed information system,like, Direct Numerical Control. Instead,Distributed Numerical Control is introduced. In

such a system, a host computer communicatewith many CNC machine tools via networksand download or upload programs.

Distributed Numerical Control (DNC):


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With Distributed Numerical Control systems, itis possible to monitor the activities in individualCNC machine tools on host computer.Therefore, better shop floor control can beachieved.


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NC program preparation may be tedious anddifficult if the part to be machined has acomplex geometry. The main difficulty is tofind out the cutter locations during themachining. Computers may be used to assistthe programmers in preparing the NC codes.

Computer Aided Part Programming:


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Advantages of applying computer-aided partprogramming include the following:

1. It reduces the manual calculationsinvolves in determining the geometriccharacteristics of the part.It provides the cutter path simulation.

It provides tool collision checking.It shortens the program preparation time.It makes the program preparation easier.

Th A I d t i A i ti


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The Aerospace Industries Associationsponsored the work that led to the first partprogramming language, developed in MIT in1955.This was called: Automatically Programmed Tools (APT).

APT is an English like simple programminglanguage which basically produce the Cutter Location (CL) data.

Using the cutter location data, the program cangenerate the actual NC codes by using apostprocessor .

CAD/CAM Based Part Programming:


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The output of any CAD package include thegeometric data of the part to be machined.Therefore, many CAD/CAM package canproduce cutter location (CL) data to be usedfor NC code generation.There is still to be a process planning modulefor a workable NC code generation.Some of the CAD/CAM packages that have theNC code generation capabilities areComputervision, CATIA, CADAM, ProEngineer,

19647980 cnc machine tools

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