• cnc stands for computer numerical control. • it is

8/14/2019 CNC Stands for Computer Numerical Control. It Is

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CNC

CNC stands for Computer Numerical Control.

It is a versatile system that allows you to control themotion of tools and parts through computer programs

that use numeric data.

CNC can be used with nearly any traditional machine.


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The most common CNC machines found in the

machine shop include machining centers (mills)

and turning centers (lathes).

CNC finds applications in other processes such

as sheet metal working, non-traditional

machining and inspection. Robots and Rapid

Prototyping machines are also CNC controlled


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CNC Vs Automates

Automats and Special Purpose Machines (SPMs)

require special cams / templates and clutch

settings for each part. Manufacture of these cams /templates is costly and slow. Furthermore,

changing over from one part to the other on these

machines also consumes considerable time. The

high cost and long time of these hard automatedmachines to produce parts can be justified only in

mass production. These are avoidedwith CNC


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Advantages of CNC

Flexibility

Accuracy

Speed Simplified fixture and generic cutting

tools

Storage of machining skill in NC

programs

Less skilled operators will do

Less fatigue to the operators


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Part drawingPart

programming CNC Machinetool

Programming Operation

BASIC FLOW FOR CNC PREPARATION


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Servo

MotorSlide

Axisservo

controller

Computer

Numerical

Control

Encoder

Programmable

Machine

controller

User

Interface

(keyboard,monitor)

Machine Tool

BASIC FUNCTIONAL BLOCKS OF A CNC MACHINE


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Turning center

Turning centerA sophisticated CNC machine that specializes in

turning, boring, drilling, and threading

operations, all at the same location.

Spindle

The part of the machine tool that spins. On themachining center, the spindle holds a cutting

tool. On the turning center, the spindle holds

the work piece.


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Turning center

Turret

This holds the tools required for machining.

Usually on a turret in the rear, most lathes have 8

to 12 tools on a single, indexing turret.

Gang-type lathes have no turret, tools are mounted

on a cross-slide for short motions.


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Turning center

Axis

This is the moving slide and a turning center

has a minimum of two axes.(named x and z).

controlled by the CNC.

The turret is mounted on the axes

in such a way that,The tool can be moved in

both directions.


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Turning center

z

x

Zaxis

Xaxis


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Functions

Auxiliary function ( M functions)

Preparatory functions ( G functions)

Spindle function

Feed function

Tool function


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Auxiliary function

M codes M codes are used for doing auxiliary machine

functions.

It is designated by M followed by No.

Example

M08 Coolant OnM06 Tool change


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M00 Program Stop Temporary stop of program

M01 Optional Stop Temporary stop of program ( Optiontion Stop )

M02 Program end Program end and reset

M03 Spindle normal rotation Clockwise rotation of spindle

M04 Spindle reverse rotation Counter clockwise rotation of spindle

M05 Spindle Stop Spindle rotation stop

M06 Tool Change ATC Cycle start

M08 Coolant ON Coolant DischargeM09 Coolant OFF Coolant shut

M22 IndexForward Turretindexclockwise

M23 IndexReversed Turretindexcounterclockwise

M24 Chuck open Openingofchuck

M25 Chuck close Closing ofchuck

M30 Program end and rewind Program end and reset/rewind

M98 Sub-program call Call of a sub-program from a main program

M99 Sub-program end Return from a sub-program to a main program


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Preparatory function

(G-codes)

G00 Positioning (Rapid Traverse)

G01 linear interpolation(Cutting feed)

G02 Circular interpolation (CW)

G03 Circular interpolation (CCW)

G04 Dwell G20 Input in inches


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G21 Input in millimeters

G28 Return to reference point

G32 Thread cutting

G40 Tool nose radius compensation cancel

G41 Tool nose radius compensation left

G42 Tool nose radius compensation right


(G-codes)


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G50 Programming of absolute zero point

G50 Maximum spindle speed setting

G70 Finishing cycle

G71 Stock removal in turning

G72 Stock removal in facing

G73 Pattern repeating


(G-codes)


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G74 Peck drilling cycle - z axis

G90 Absolute programming

G91 Incremental programming

G92 Thread cutting cycle

G96 Constant surface speed control

G97 Constant surface speed control cancel

G98 Per minute feed

G99 Per revolution feed


(G-codes)


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CNC programming

What is programming ?

Programming is telling the machine by

command data through numerical control

for its working of its components.

Example :

Movement of Turret..

Rotation of spindle etc


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Program block

A program block is a combination of above functions in a

single line.

Example : N01 G01 G91 X0.0 Y10.0 S2000 M03 ;

SEQUENCE

NUMBER

END OF BLOCK

Line number is optional

End of block is mandatory


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Sequence Number

Designated as N1 or N10 etc

Used to identify the blocks

Not mandatory Occupies memory

Can be used for each process rather

than for each block


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Spindle speed Function

The spindle speed can be specified by a S code followed by a

Numerical value (rpm).

Syntax :S ;

Example : S2000 M03;

Usually S command is associated with M03 or M04 to specify

the direction of rotation CW or CCW


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Spindle speed function

CONSTANT SURFACE SPEED CONTROL (CSS CONTROL)

As you know when the tool is moving towards the center the cuttingspeed changes.

Vc = DN/1000

In CSS control N is varied automatically to keep the Vc constant

when the tool moves diametrically.

Syntax : G96 S200; CSS Control on

G97; CSS control cancel

G96 and G97 are modal codes.Here S200 denotes the cutting speed.


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Spindle speed function

CLAMP OF MAXIMUM SPINDLE SPEED

When we are using G96, the CSS control, the spindle Speed

need to be clamped to a maximum speed.

This is done with a preparatory function G50

Syntax : G50 S3500;

Spindle speed is clamped to a maximum of 3500 rpm.


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Feed function

The feed can be specified by F code followed by a Numerical

value (feed per minute / feed per revolution).

Syntax :F ;

Example : G98 F100;: G99 F0.15;

G98 and G99 are preparatory functions to specify feed per

minute and feed per revolution respectively.


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Tool function

Tool selection

A 2 digit / 4 digit numeric followed by a T code is used

to select the required tool.

Syntax T

Example T0303; Selects turret 3 with offset Nr.03

T0313; Selects turret 3 with offset Nr.13

Tool number Offset number


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Tool offset

Tool offset is a value used to compensate the difference between

the actual tool and the imagined tool (standard tool) used for

programming.

Standard tool

Actual tool

Z offset

X offset


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Tool offset

Tool Geometry offset:

To compensate the difference in tool shape and mounting position.

Tool Wear offset:

To compensate the tool wear during running.

Example : T0202 Calls the offset Nr.02

: T0200 Offset cancel


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How to Enter the Tool Offset ?

There are two methods to enter the tool offset value

From the offset entry screen

From inside the program (G10 programming)


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Offset Entry Screen

OFFSET/GEOMETRYO0001 N0000

NO. X. Z R T

G 001

G 002

G 003

G 004

G 005

G 008

G 006

G 007

0.000

1.486

1.322

0.567

0.873

-0.435

-0.085

0.654

0.000

1.486

1.322

0.567

0.873

-0.435

-0.085

0.654


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Evolution of

CNC programming

Punched tape and input through tape reader Programming directly on the machine

Programming through hand held device

Programming from centralized PC


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CNC programming

Process of Programming

Part drawing - indicates which are the

characteristics to be machined

Machining plan how many set ups, fixtures, tooling,

sequence of operation etc

Part programming Writing program considering the

machining plan


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How to set the machine

Machine ON

Origin

Fixture Mounting

Fixture dialing

Locator/clamp fixing

Tool mtg on the holders

Measure the tool length

Tool pocketing


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Tool offset inputing

Programming

Find work co ordinate

Dry run with out component

/single block

Cutting in single block

Rapid /feed lesser rate

Component inspection

Correction of work co ordiante

Correction of tool offset

Component cutting @

100% feed/ speed/Rapid


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Popular CNC Controls

FanucSinumeric from Siemens

Heidenhain

Allen Bradley etc

We will discuss on FANUC .


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Program Number

Program number

The program no is used to arrange several

programs in order

The program no is expressed by putting

numerals of 4 digits after the alphabet O

Ex O 1234


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Block

O1234;

N10 GOO G9O G54 X0 Y0;

Each line is block


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Work piece zero point

The reference point on the work piece is called

work piece zero point.

Determine the work piece zero point wrtdrawing dimensioning or having easy

reference to drawing.


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Absolute command

The point with reference to the work piece

zero point is referred as absolute command

Always referred by G90


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Incremental command

The point with reference to the present

position . No reference to the work piecezero point

Always referred by G91


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Basic Programming rulesCNC lathe :

X = The diameter of the part.Z = The length dimension

Usually Z is set at the finished face of thepart, any cut into the part is a minus value.

A positive value in the program indicates it isclear of the part, a minus value indicates it isinto the part.


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Programming for Turning center

Turning center - Work coordinate principle

x +

Spindle

z(-) z (+)

Work Zero

x (-)


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Turning center

Diametrical programming

The Diametrical value of the work piece

is directly input in to the program .

X 50.05

50


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Turning center

G00 POSITIONING IN RAPID

N_ G00 X_ Z_

The G00 is a command for rapid traverse

from a starting point to a command point.


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Turning center

G01 LINEAR INTERPOLATION

N_ G01 X_ Z_ F_

The G01 is the command bywhich the tool travels to the point

specified with X & Z at thespeed specified with F code.


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Turning center

G02 CIRCULAR INTERPOLATION

(CW)

N_ G02 X_ Z_ R_ F_The G02 is a clockwise

radial feed move

Z axis

GO2

X axis


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Turning center

G03 CIRCULAR INTERPOLATION

(CCW)

N_ G03 X_ Z_ R_ F_The G03 is a counter

clockwise radial

feed move

Z axis

GO3

X axis


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Turning center

G04 DWELL

N_ G04 U or P_

The G04 is a dwell command that halts the

feed movement for the time as specified

by U or P.


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Turning center

G20 INCH UNITS

N_ G20

The G20 command defaults the system to

inch units. When a program is being run

and the G20 command is encountered, all

coordinates are stated as inch units


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Turning center

G21 METRIC UNITS

N_ G21

The G21 command defaults the system to

metric units. When a program is being run

and the G21 command is encountered, all

coordinates are stated in as millimeter units.


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Turning center

G28 AUTOMATIC RETURN TO

REFERENCE

N_ G28 X_ Z_The G28 allows the existing tool to be

positioned to the machine zero point via an

intermediate position.


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Turning center

G32 threading

G32 is used to cut straight & taper thread

G32 Z F for straight thread , F is the Pitch

G32 X Z F for taper thread ,F is the Pitch


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Turning center

G40 CUTTER COMPENSATION

CANCEL

N_ G40The G40 cancels any cutter compensation that was

applied to the tool during a program and acts as a

safeguard to cancel any cutter compensation

applied to a previous program or G-codes.


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Turning center

G41 CUTTER COMPENSATION LEFT

N_ G41

The G41 compensates the cutter a specified

distance to the left-hand side of the

programmed tool path. Shift the offset

amount to the left of machining surface.


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Turning center

G42 CUTTER COMPENSATION

RIGHT

N_ G42

The G42 compensates the tool a specified

distance to the right-hand side of the

programmed tool path. Shift the offsetamount to the right of machining surface.


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Turning center

CUTTER COMPENSATION

G40 G41 G42


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Turning center

G50 Co ordinate setting

Max spindle speed setting.

To assign the work co ordinate value as

well as max spindle speed setting this

command is used

G 50 X_ Z_ Co ordinate setting

G50 S 2500 max spindle speed setting


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Turning center

G 50 X 200. Z100

100

100

STOCK REMOVAL IN TURNING G71


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STOCK REMOVAL IN TURNING G71

G71 U(dd)__ R__

G71 P__ Q__ U(du)__ W__ F__ S__ T__

G71 Stock Removal in Turning

U(dd) Depth of cut

R Escaping amount

P Sequence no. of the first block for the program of finishingshape.

Q Sequence no. of the last block for the program of finishingshape.

U(du) Distance and direction of finishing allowance in X direction

W Distance and direction of finishing allowance in Z direction F Feed

S Speed

T Tool No

STOCK REMOVAL IN TURNING G71STOCK REMOVAL IN TURNING G71


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STOCK REMOVAL IN FACING G72


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STOCK REMOVAL IN FACING G72

G72 W(dd)__ R__

G72 P__ Q__ U__ W(dw)__ F__ S__ T__

G72 Stock Removal in Facing

W(dd) Depth of cut

R Escaping amount

P Sequence no. of the first block for the program of finishing shape.

Q Sequence no. of the last block for the program of finishing shape.

U Distance and direction of finishing allowance in X direction

W(dw) Distance and direction of finishing allowance in Z direction F Feed

S Speed

T Tool No

STOCK REMOVAL IN FACING G72STOCK REMOVAL IN FACING G72


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PATTERN REPEATING CYCLE G73


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PATTERN REPEATING CYCLE G73

G73 U(di)__ W(dk)__ R__

G73 P__ Q__ U(du)__ W(dw)__ F__ S__ T__

G73 Pattern Repeating

U(di) Distance and direction of relief in the X-axis direction

W(dk) - Distance and direction of relief in the Z-axis direction

R No of division ( repetitive count for rough cutting )

P Sequence no. of the first block for the program of finishing shape.

Q Sequence no. of the last block for the program of finishing shape.

U(du) Distance and direction of finishing allowance in X direction

W(dw) Distance and direction of finishing allowance in Z direction

F Feed

S Speed

T Tool No

PATTERN REPEATING G73PATTERN REPEATING G73


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PATTERN REPEATING G73PATTERN REPEATING G73


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FINISHING CYCLE G70

After rough cutting by G71, G72 or G73, thefollowing command permits finishing

G70 P__ Q__

G70 - Finishing cycle

P - Sequence no. of the first block for the program offinishing shape.

Q - Sequence no. of the last block for the program offinishing shape.


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Turning center

34

4

3 1

2

70

G92 THREAD CUTTING CYCLE

G28 U0 WO

G50 X 220. Z167.0

G97 S650 T5005 M3

G99

G00 X70.0 Z80.0 M8

M36

G92 U-10.8 Z34.0 F3.0

U-12.0

U-12.5

U-12.8

U-12.9

U-13.0

G28 U0 WO M9


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Turning center

G96 Constant surface speed control

G96 is used when cutting speed is required

to be specified

G96

Ex facing To have common cutting speed


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Turning center

G97 Constant surface speed control cancel

G97 is used when spindle speed is required to

be specified

G97

Ex Drilling To have common cutting speed


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Turning center

G98 Feed per minute

G98 is used to specify the tool movement inmm per minute

G98

Ex bar bulling


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Turning center

G99 Feed per Revolution

G99 is used to specify the tool movement inmm per spindle revloution

G99

Ex Regular turning


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- OD THREAD -

N9G28U0W0G50X220.0Z163.5G97S400T500M3G99G00X110.0Z80.0T5M8G92U-10.7Z51.0F2.0U-11.2U-11.6

U-11.92U-12.12U-12.26U-12.36U-12.46U-12.5G28U0W0M9

M1M30

• cnc stands for computer numerical control. • it is

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