Introduction to CNC Technology (in Powerpoint Format)

8/14/2019 Introduction to CNC Technology (in Powerpoint Format)

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CNC

TECHNOLOGY


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INTRODUCTION TO

CNC AND METALCUTTING


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HISTORY

US Air Force commissioned MIT to develop thefirst "numerically controlled" machine in 1949. Itwas demonstrated in 1952.

At 1970-1972 first Computer Numeric Controlmachines 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 amicro-computer attached to the machine.

The computer will also handle much of thecontrol logic of the machine, making itmore adaptable than earlier hard-wired

controllers.


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CNC APPLICATIONS

Machining

2.5D / 3D

Turning ~ Lathes, Turning Centre

Milling ~ Machining Centres Forming

2D

Plasma and Laser CuttingBlanking, nibbling and punching

3D

Rapid 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

Aerospace

Machinery

Electrical Fabrication

Automotive

InstrumentationMold making


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SAMPLE PRODUCTS

OFCNC MANUFACTURING

AUTOMOTIVE INDUSTRY


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AUTOMOTIVE INDUSTRY

Engine Block


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AEROSPACE INDUSTRY


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AEROSPACE INDUSTRYAircraft 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


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Utilization of computers in

manufacturing applications hasproved to be one of the most

significant advantages &developments over the last coupleof decades in helping to improve

the productivity and efficiency ofmanufacturing systems.


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ADVANTAGES of CNC

Productivity

Machine utilisation is increased becausemore time is spent cutting and less time istaken by positioning.

Reduced setup time increases utilisationtoo.


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PROFITincreases as COST decreasesand as PRODUCTIVITYincreases.

PRODUCTIVITY through AUTOMATION


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AUTOMATION

any means of helpingthe workers to performtheir tasks more

efficiently

transfer of the skill ofthe operator to themachine


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Transferred

skillResults

muscle power engine drivenmachine tools

First industrial

revolution

manipulating

skill

mechanization hard automation

vision skill use of positiontransducers,

cameras

increase of

accuracy, part

recognition

brain power cnc machines, industrialrobots, soft

automation,

computer control of

manufacturing

systems

second industrial

revolution


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EFFICIENCY OF

MANUFACTURING

COST = COST OFMANUFACTURING ANDCOST OF MATERIAL

HANDLING

PROFIT = INCOME - COST

PRODUCTIVITY =

AVERAGE OUTPUT PERMAN-HOUR


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ADVANTAGES of CNC

Quality

Parts are more accurate.

Parts are more repeatable.Less waste due to scrap.


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ADVANTAGES of CNC

Reduced inventory

Reduced 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 shapes

Slide 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 Control

CNC leads to CAD

Process planningProduction planning


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FUNDAMENTAL OFMETAL CUTTING


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The metal cutting operations (alsocalled machining)is one of the

most important manufacturingprocesses 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 relationship in

such a way as to achieve a desiredgeometric shape of the workpiece

with sufficient dimensionalaccuracy.


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Machine tool provides:

work holdingtool holding

relative motion between tooland workpiece

primary motionsecondary motion


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Primary motion

Relative motionbetween tool and

workpieceSecondary motion

Cutting motion

Cuttingspeed

Feed motion

Feed rate


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CLASSIFICATION OF THE CHIP REMOVINGMETHODS ACCORDING TO THE RELATIVE MOTION


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CLASSIFICATION OF MACHINE TOOLS

THOSE USING

SINGLE

POINTTOOLS

THOSE USING

MULTIPOIN

T TOOLS

THOSE USING

ABRASIVE

TOOLS

lathes

shapers

planersboring m/cs

etc.

drilling m/cs

milling m/cs

broaching m/cshobbing m/cs

etc.

grinding m/cs

honing m/cs

etc.


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BASIC COMPONENTSOF CNC SYSTEMS


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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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ISO MACHINE TOOL AXIS DEFINITION

ISO MACHINE TOOL AXES DEFINITIONS


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AXIS MACHINE TOOL WITH SPINDLE MACHINE TOOL WITHNO SPINDLE

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

perpendicular to work

holding surface, (+Z) as

tool goes away from theworkpiece

MACHINE

TOOL WITH

ROTATING

WORKPIECE

MACHINE TOOL WITH

ROTATING TOOL

HORIZONT

AL AXIS

VERTICAL

AXIS

X radial andparallel to

cross slide,

(+X) when

tool goes away

from the axis

of spindle

horizontal

and parallel

to work

holding

surface,

(+X) to the

right whenviewed

from

spindle

towards

work piece

horizontal

and parallel

to the work

holding

surface,

(+X) to the

right whenviewed

from

spindle

towards

column

parallel to and positive in

the principal direction of

cutting (primary motion)

Y apply right hand rules


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RIGHT HAND RULEVertical Machine Horizontal Machine

STANDARD LATHE


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STANDARD LATHECOORDINATE SYSTEM

STANDARD MILLING MACHINE


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STANDARD MILLING MACHINECOORDINATE 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 offmoving tool with respect to workpiece

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


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MACHINE TOOLAUTOMATION


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CNC SYSTEM ELEMENTS

A typical CNC system consists of thefollowing six elements

Part program

Program input deviceMachine control unit

Drive system

Machine tool Feedback system


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NC SYSTEM ELEMENTS

OPERATIONAL FEATURES f


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OPERATIONAL FEATURES ofCNC MACHINES


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PART PROGRAM A part program is a series of coded instructions required

to 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 functional

blocks as in the following exampleN10 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 beentered into the CNC control. The most

commonly used program input devices arekeyboards, punched tape reader, diskettedrivers, throgh RS 232 serial ports and

networks.

MACHINE CONTROL UNIT


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MACHINE CONTROL UNITThe machine control unit (MCU) is the heart of a CNC

system. It is used to perform the following functions:

Read coded instructions

Decode coded instructions

Implement interpolations (linear, circular, and helical) togenerate axis motion commands

Feed axis motion commands to the amplifier circuits fordriving the axis mechanisms

Receive the feedback signals of position and speed foreach drive axis

Implement 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

OPEN LOOP CONTROL


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OPEN-LOOP CONTROLSYSTEM

In open-loop control system step motors areused

Step motors are driven by electric pulses

Every pulse rotates the motor spindle through acertain amount

By counting the pulses, the amount of motioncan be controlled

No feedback signal for error correction Lower positioning accuracy

CLOSED LOOP CONTROL


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CLOSED-LOOP CONTROLSYSTEMS

In closed-loop control systems DC or ACmotors are used

Position transducers are used to generate

position feedback signals for errorcorrection

Better accuracy can be achieved

More expensive Suitable for large size machine tools


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CONTROL

Desired path (p, v, a)

3-axis position control (encoder feedback)

Velocity control (tachometer feedback) Torque control (current feedback)

Path generator

Linear interpolation Circular interpolation

Complex path interpolation (contouring)


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DRIVE SYSTEM

A drive system consists of amplifiercircuits, stepping motors or servomotorsand ball lead-screws. The MCU feeds

control signals (position and speed) ofeach axis to the amplifier circuits. Thecontrol signals are augmented to actuatestepping motors which in turn rotate the

ball 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 rotary

motion of the motor shaft into linear motion ofthe workpiece .


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STEPPING MOTORS

RECIRCULATING BALL


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RECIRCULATING BALLSCREWS

Transform rotational motion of the motorinto translational motion of the nut attached to themachine table.

RECIRCULATING BALL


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RECIRCULATING BALLSCREWS

Accuracy of CNCmachines depends ontheir rigid

construction, care inmanufacturing, andthe use of ball screwsto almost eliminate

slop in the screwsused to move portionsof the machine.

COMPONENTS OF


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COMPONENTS OFRECIRCULATING BALL SCREWS

Ball screw

Ball nut (anti-backlash)

Ways Linear bearings


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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 of0.0025 mm or better.


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MACHINE TOOL

CNC controls are used to control varioustypes of machine tools. Regardless ofwhich type of machine tool is controlled, it

always has a slide table and a spindle tocontrol of position and speed. Themachine 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 andspeed transducers to continuously monitor

the position at which the cutting tool islocated at any particular time. The MCUuses the difference between referencesignals and feedback signals to generate

the control signals for correcting positionand speed errors.


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CNC MACHINES FEEDBACK

DEVICES

ENCODERS


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ENCODERS

A device used to convert linear orrotational position information intoan electrical output signal.


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ENCODERS

INDUSTRIAL APPLICATIONS of


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INDUSTRIAL APPLICATIONS ofENCODERS


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RESOLVERS

A resolver is a rotarytransformer that producesan output signal that is a

function of the rotorposition.

SERVOMOTOR with


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RESOLVER


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DRIVE MOTORS

DC servo motors

AC servo motors

Stepper motors

Hydraulic motors

OS O C


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POSITION FEEDBACK

Incremental encoder

Quadrature

Absolute encoder

Resolver Tachometer

No feedback (open

loop)

POTENTIOMETERS


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POTENTIOMETERS

POTENTIOMETERS


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POTENTIOMETERS

CNC P i


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CNC Programming

Manual Write code directly

Computer-assisted

Draw cutter path

CAD/CAM

Draw the part

Cutter path is generated

VELOCITY FEEDBACK


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VELOCITY FEEDBACK

Tachometers:Electrical output is proportional to rate ofangular rotation.

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


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CNC MACHINES

CUTTING TOOLS (CUTTERS)

CNC CUTTERS


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CNC CUTTERS

Turning center cutters

Machining center cutters

TURNING CENTER CUTTERS


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TURNING CENTER CUTTERS

Types of cutters used on CNC turningcenters

Carbides (and other hard materials) insert

turning and boring toolsCeramics

High Speed Steel (HSS) drills and taps

STANDART INSERT SHAPES


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STANDART INSERT SHAPES

Vused for profiling, weakestinsert, 2 edges per side.

Dsomewhat stronger, used forprofiling when the angle allows it,2 edges per side.

Tcommonly used for turning

because it has 3 edges per side. Cpopular insert because the

same holder can be used forturning and facing. 2 edges perside.

Wnewest shape. Can turn andface like the C, but 3 edges per

side. SVery strong, but mostly used

for chamfering because it wontcut a square shoulder. 4 edgesper side.

Rstrongest insert but leastcommonly used.

,THREADING and PARTING


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THREADING and PARTINGTOOLS

MACHINING CENTER CUTTING


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TOOLS Most machining centers

use some form of HSS orcarbide insert endmill asthe basic cutting tool.

Insert endmills cut manytimes faster than HSS,but the

HSS endmills leave a

better finish when sidecutting.



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TOOLS (contd)

Facemills flatten largesurfaces quickly andwith an excellentfinish. Notice theengine block beingfinished in one passwith a large cutter.



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TOOLS (contd)

Ball endmills (bothHSS and insert) areused for a variety ofprofiling operations

such as the moldshown in the picture.

Slitting and sidecutters are used when

deep, narrow slotsmust be cut.



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TOOLS (contd)Drills, Taps, and Reamers

Common HSS tools such asdrills, taps, and reamers arecommonly used on CNCmachining 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 pull

stud 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 years

ago as an improvement to CAT tapers,but they are gaining acceptance slowly.


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CNC PROGRAMMING

CNC PROGRAMMING


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CNC PROGRAMMING

Offline programminglinked to CAD programs. Conversational programmingby the operator.

MDI~ Manual Data Input.

Manual Controlusing jog buttons or `electronichandwheel'.

Word-Address Codingusing standard G-codesand M-codes.

Basics of NC Part Programming


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During secondary motion, either the toolmoves relative to the workpiece or the

workpiece moves relative to the tool. InNC programming, it is always assumed

that the tool moves relative to the

workpiece no matter what the realsituation is.

Basics of NC Part Programming:


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The position of the tool is describedby using a Cartesian coordinatesystem. If (0,0,0) position can be

described by the operator, then it iscalled floating zero.


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In defining the motion of the toolfrom one point to another,either

absolutepositioningmode orincrementalpositioningmode

can be used.


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Structure of an NC Part Program:

Commands are input into the controller inunits called blocksor 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 08

0070 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

Modal commands: Commands issued in the


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Modal commands: Commands issued in theNC program that will stay in effect until it is

changed 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

INFORMATION NEEDED by a


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CNC

1. Preparatory Information: units, incremental or absolutepositioning2. Coordinates: X,Y,Z, RX,RY,RZ3. Machining Parameters: Feed rate and spindle speed4. Coolant Control: On/Off, Flood, Mist

5. Tool Control: Tool and tool parameters6. Cycle Functions: Type of action required7. Miscellaneous Control: Spindle on/off, direction of

rotation, stops for part movement

This information is conveyed to the machine through a setof instructions arranged in a desired sequenceProgram.

BLOCK FORMAT


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Sample BlockN135 G01 X1.0 Y1.0 Z0.125 F5

Restrictions on CNC blocks Each may contain only one tool move Each may contain any number of non-tool move G-

codes Each may contain only one feedrate Each may contain only one specified tool or spindle

speed The block numbers should be sequential Both the program start flag and the program number

must be independent of all other commands (onseparate lines)

The data within a block should follow the sequence

WORD-ADDRESS CODING


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WORD-ADDRESS CODING

N5 G90 G20 N10 M06 T3 N15 M03 S1250

N20 G00 X1 Y1 N25 Z0.1 N30 G01 Z-0.125 F5 N35 X3 Y2 F10 N40 G00 Z1

N45 X0 Y0 N50 M05 N55 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 ofinformation needed by the machine.

Letters used in Codes

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

G & M Codes


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G & M Codes

N5 G90 G20 N10 M06 T3 N15 M03 S1250

N20 G00 X1 Y1 N25 Z0.1 N30 G01 Z-0.125 F5 N35 X3 Y2 F10 N40 G00 Z1

N45 X0 Y0 N50 M05 N55 M30

Example CNC Program

G-codes: Preparatory Functionsinvolve actual tool moves.

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

G Codes


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G Codes

G00 Rapid traverse G01 Linear interpolation

G02 Circular interpolation,CW

G03 Circular interpolation,CCW

G04 Dwell

G08 Acceleration

G09 Deceleration

G17 X-Y Plane

G18 Z-X Plane

G19 Y-Z Plane

G20 Inch Units (G70) G21 Metric Units (G71)

G40 Cutter compensationcancel

G41 Cutter compensationleft

G42 Cutter compensation-right

G70 Inch format G71 Metric format G74 Full-circle programming

off G75 Full-circle programming

on G80 Fixed-cycle cancel G81-G89 Fixed cycles G90 Absolute dimensions G91 Incremental dimensions

Modal G-Codes


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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. Thesecommands are called modal.

Modal G-Code List


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Modal G-Code List

G00 Rapid Transverse G01 Linear Interpolation

G02 Circular Interpolation, CW

G03 Circular Interpolation,CCW

G17 XY Plane

G18 XZ Plane

G19 YZ Plane G20/G70 Inch units

G21/G71 Metric Units

G40 Cutter compensationcancel

G41 Cutter compensation left

G42 Cutter compensation right

G43 Tool length compensation(plus)

G43 Tool lengthcompensation (plus)

G44 Tool lengthcompensation (minus)

G49 Tool lengthcompensation cancel

G80 Cancel canned cycles

G81 Drilling cycle

G82 Counter boring cycle

G83 Deep hole drilling cycle

G90 Absolute positioning

G91 Incremental positioning

M Codes


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M Codes

M00 Program stop M01 Optional program stop M02 Program end M03 Spindle on clockwise M04 Spindle on counterclockwise M05 Spindle stop M06 Tool change M08 Coolant on M09 Coolant off M10 Clamps on M11 Clamps off M30 Program stop, reset to start

N Codes


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N Codes

Gives an identifying number for each blockof information.

It is generally good practice to incrementeach block number by 5 or 10 to allowadditional blocks to be inserted if future

changes are required.

X Y and Z Codes


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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 the

coordinate at the end of the move relativeto an incremental or absolute referencepoint.

I J and K Codes


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I,J, and K Codes

I, J, and K codes are used to specify thecoordinate axis when defining the centerof a circle.

Number following the code defines therespective coordinate for the center of the

circle.

F S and T Codes


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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 CodesG01 Li I t l ti


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G01 Linear Interpolation

Format: N_ G01 X_ Y_ Z_ F_

Linear Interpolation results in a straight

line feed move.

Unless tool compensation is used, the

coordinates are associated with thecenterline of the tool.



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

the axes is completed and then the balance ofthe motion occurs in the other axis. This is called

point-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 referred

to 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



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N10 G00 X1 Z1N15 Z0.1N20 G01 Z-0.125 F5

N25 X2 Z2 F10


X

Z

G02 Circular Interpolation


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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 end

point of the arc and the location of the center ofthe 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 Circular Interpolation (CW)


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The G02 command requiresan endpoint and a radius inorder to cut the arc.

I,J, and K are relative to the

start point.

N_ G02 X2 Y1 I0 J-1 F10

or

N_ G02 X2 Y1 R1



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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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The sequence of some machining operations is maybe the same for any part and for any machine. Forexample drilling a hole involves the following steps:Position the tool above the point where the hole will bedrilledSet the correct spindle speedFeed the tool into the workpiece at a controlled feedrate to a predetermined depthRetract the tool at a rapid rate to just above the pointwhere the hole started

Some Commonly Used Canned Cycle

C d F ti D f d At b tt R t ti


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Code Function Down feed At bottom Retraction

G81 Drilling Continuousfeed

No action Rapid

G82 Spot face,counterbore

Continuous

feedDwell Rapid

G83 Deep hole drilling Peck No action Rapid

G84 Tapping Continuousfeed

Reverse

spindleFeed

rate

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

G86 Through boring(inonly)

Continuous

feedStop

spindleRapid

G81 ILLUSTRATION


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Three Main parts of a CNCprogram


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program

N5 G90 G21 (Absolute units, metric)

N10 M06 T2 (Stop for tool change, usetool # 2)

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

Part 1- Program Petup



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program

N20 G00 X1 Y1 (Rapid to X1,Y1 from origin

point) 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



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program

N50 M05 (Turn the spindle off)

N55 M00 (Program stop)

Part 3- System Shutdown

EXAMPLE OPERATION on CNCMILLING MACHINE


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MILLING MACHINE

G-CODE PROGRAM


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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 Y0.125N30 Z0.125N35 G01 Z-0.125 F5

N40 X3.875N45 Y4.125N50 X0.125N55 Y0.125

Second pass:


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conventional mill to a

depth of 0.25 aroundedge profile.

N35 Z-0.250

N40 X3.875

N45 Y4.125

N50 X0.125

N55 Y0.125

N60 Z0.125

Third pass:conventional mill to a


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co e t o a to adepth of 0.125 around

pocket profile.

N65 G00 X1.25 Y1.0

N70 G01 Z-0.125 F5

N75 X1.75

N80 Y2.5

N85 X1.25

N90 Y1.0N95 Z0.125

Fourth pass: climbmill to a depth of


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mill to a depth of0.125 acrossremaining material.

N100 Y2.125

N105 X2.625N110 Z0.125

N115 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 reader Through diskette drive

Through RS 232 serial port

Through network interface card


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Direct Numerical Control (DNC):


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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 information wouldbe 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, DistributedNumerical Control is introduced. In such a

system, a host computer communicate withmany CNC machine tools via networks anddownload 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 to findout the cutter locations during the machining.Computers may be used to assist theprogrammers in preparing the NC codes.

Computer Aided Part Programming:

Advantages of applying computer aided part


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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.

The Aerospace Industries Association


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The Aerospace Industries Associationsponsored the work that led to the first part

programming language, developed in MIT in1955.

This was called:Automatically ProgrammedTools(APT).

APT is an English like simple programminglanguage which basically produce the CutterLocation(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 used for

NC code generation. There is still to be a process planning module

for a workable NC code generation.

Some of the CAD/CAM packages that have the

NC code generation capabilities areComputervision CATIA CADAM

Introduction to CNC Technology (in Powerpoint Format)

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Transcript of Introduction to CNC Technology (in Powerpoint Format)