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What is CNC?

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CNC stands for Computer Numerical Control.

It is a versatile system that allows you to

control the motion of tools and parts throughcomputer programs that use numeric data.

CNC can be used with nearly any traditionalmachine.

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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 ofthese 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 timeof these hard automated machines 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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Slide

Axis servo

controller

Computer

Numerical

Control

Encoder

Programmable

Machine

controller

User

Interface

(key board,monitor)

Machine Tool

BASIC FUNCTIONAL BLOCKS OF A CNC MACHINE

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Popular CNC Controls

FanucSinumeric from Siemens

Heidenhain

Allen Bradley etc

We will discuss only FANUC .

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What is a turning center?

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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 theturning center, the spindle holds the work

piece, On the machining center, the spindle

holds a cutting tool.

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TurretThis holds the tools required for machining.

Usually on a turret in the rear, most latheshave 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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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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z

x

Z axis

Xaxis

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Turning center Operations

Facing

Turning

DrillingBoring

Grooving on OD or ID

Face grooving

Chamfering

Thread Cutting

Etc.,,

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Functions

Auxiliary function ( M functions)

Preparatory functions ( G functions)

Spindle function

Feed function

Tool function

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M codes

M codes are used for doing auxiliary

machine functions.

It is designated by M followed by No.

Example

M08 Coolant On

M06 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 Discharge

M09 Coolant OFF Coolant shut

M22 Index Forward Turret index clockwise

M23 Index Reversed Turret index counter clockwise

M24 Chuck open Opening of chuck

M25 Chuck close Closing of chuck

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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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

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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

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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

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What is programming?

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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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What are various Functions ?

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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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CONSTANT SURFACE SPEED CONTROL (CSS CONTROL)

As you know when the tool is moving towards the center the cutting

speed changes.

Vc = DN/1000In CSS control N is varied automatically to keep the Vc constant

when the tool moves diametrically.

Syntax : G96 Vc; CSS Control on

G97; CSS control cancel

G96 S200;

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

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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

Example : 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

T0300; Cancels current offset.

Tool number

Offset number

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Lets see some G codes

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G01 Linear interpolation

N_ G01 X_ Z_ F_

The G01 is the command by which the tool

travels to the point specified with X & Z at the

speed specified with F code.

G01 X-50.0F0.15;

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G90- Absolute command

The point with reference to the work piece

zero point is referred as absolute command

Always referred by G90

Example : G90 X20.0 Z20.0;

Refers to a point 20mm away from the work

zero in both x and z directions.

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G91 - Incremental command

The point with reference to the present

position . No reference to the work piece zero

point. Always referred by G91

Example : G91 X20.0 Z20.0;

Refers to a point 20 mm away from the

current position in both x and z directions.

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G02 Circular interpolation (cw)

N_ G02 X_ Z_ R_ F_

The G02 is a clockwiseradial feed move

Z axis

GO2

X axis

http://www.cncezpro.com/Images/GCodes/Milling/g02/g02m.gif',%20'Demo',%20'width=260,height=200,toolbar=0,location=0,directories=0,status=0,menuBar=0,scrollBars=0,resizable=0http://www.cncezpro.com/Images/GCodes/Milling/g02/g02m.gif',%20'Demo',%20'width=260,height=200,toolbar=0,location=0,directories=0,status=0,menuBar=0,scrollBars=0,resizable=0

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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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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, allcoordinates are stated as inch units

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G28 Automatic return to

reference point

N_ G28 U_ W_

The G28 allows the existing tool to bepositioned to the machine zero point via an

intermediate position.

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G30 Automatic return to

2nd reference point

N_ G30 U_ W_

The G28 allows the existing tool to be

positioned to the machine zero point via an

intermediate position.

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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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G 50 X 200. Z100

100

100

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G96 Constant surface speed

Control

G96 is used when cutting speed is required to be

specified

G96 S425;

Ex facingTo have common cutting speed

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G97 Constant surface speed

control cancel

G97 is used when spindle speed is required to bespecified

G97

Ex DrillingTo have common cutting speed

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G98 Feed per minute

G98 is used to specify the tool movement in mm

per minute

G98

Ex bar bulling

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G99 Feed per Revolution

G99 is used to specify the tool movement in mm

per spindle revolution

G99

Ex Regular turning

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Tool offset is a value used to compensate the difference between

the actual tool and the imaginary tool (standard tool) used forprogramming.

Standard tool

Actual tool

Z offset

X offset

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Structure of a CNC program

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Evolution

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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Process of Programming

Part drawing - indicates which are the

characteristics to be machined

Machining planhow many set ups,

fixtures, tooling, sequence of operation etc

Part programmingWriting program

considering the machiningplan

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Part drawing

Part

programming CNCMachine

tool

Programming Operation

BASIC FLOW FOR CNC PREPARATION

How to set the machine

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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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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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Programming for Turning center

Turning center - Work coordinate principle

x +

Spindle

z(-) z (+)

Work Zero

x (-)

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Basic Programming rules CNC lathe :

X = The diameter of the part.

Z = The length dimension

Usually Z is set at the finished face of the part, any

cut into the part is a minus value.

A positive value in the program indicates it is

clear of the part, a minus value indicates it is into

the part.

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O ti l t d bl k ki

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Optional stop and block skip

Whenever the CNC encounters the code M01 it stops atthe same line.

Pressing Cycle start again will enable it to movefurther.

A SLASH / is used to tell the machine to skip the

particular block.

Example: /G00 X200.0;

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O7130

(PILATUS PROGRAM FOR 4130

ZEN)

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ZEN)

IF[#530NE4130]GOTO8

M98P6000

M86

G04X2.0

M01

N1 (R0UGH TURNING)

T0606

G30U0.0W0.0

G50S2000

G90G00G54X105.0Z-29.55

G96G99S375M04 M08

G01X46.0F0.4

U0.5W0.25

G00U6.0

Z0.5

X48.0

G01X20.0

G00X36.625Z1.5

G01X41.125Z-0.75

Z-29.55

G00U2.0W1.0

T0000

G30U0.0W0.0

M09

M05

#506=#506+1

M01

41.125

29.55

Turning & facing

O7130

(PILATUS PROGRAM FOR 4130

ZEN) Turning & facing

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)

IF[#530NE4130]GOTO8

M98P6000

M86

G04X2.0

M01

N1 (R0UGH TURNING)

T0606

G30U0.0W0.0

G50S2000

G90G00G54X105.0Z-29.55

G96G99S375M04 M08

G01X46.0F0.4

U0.5W0.25

Z0.5

X48.0

G01X20.0

G00X36.625Z1.5

G01X41.125Z-0.75

Z-29.55

G00U2.0W1.0

T0000

G30U0.0W0.0

M09

M05

#506=#506+1

M01

41.125

29.55

Turning & facing

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N2

(ROUGH C.BORE DV 2135)

T0808

G30U0.0W0.0

G90G00X0.0Z6.0

G97G99S1600M03

M08

G01Z-21.80F0.2

G00Z5.0

T0000

G30U0.0W0.0

M09

M05

#508=#508+1

M01

29.55

21.80

Drilling

G i

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Grooving

N6

(BOOT GROOVE)

T0303

G30U0.0W0.0

G90G00G54X44.0Z-19.85

G97G99S2000M03

M08

G01X37.625F0.25

G00X50.0

T0000

G30U0.0W0.0

M09

M05

#503=#503+1

M01

37.625

19.85

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Sub program call by M98

If i fi d f l

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If a program contains a fixed sequence or frequently

repeated pattern such a sequence or pattern can be stored

as a sub program in memory to simplify the program.

A sub program can be called from a main program

A called sub program can also call another subprogram.

EXAMPLE:

O0001;

.

.

.

M98P1000

.

.

.

M30;

O1000;

.

.

.

M98P2000

.

.

.

M99;

O2000;

.

.

.

M98P3000

.

.

.

M99;

O3000;

.

.

.

M98P4000

.

.

.

M99;

O4000;

.

.

.

.

.

.

.

M99;

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programmable data input - G10

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Offset values can be changed during run time from inside the

program by using programmable data input G10 command.

Syntax : G10 P_X_Z_;

G10 P_U_W_;

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Writing Comments in a program

A i f ti l d b t f i l b k t

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Any information enclosed by a set of circular brackets

() is regarded as a comment and the CNC

skips that line.

Comments are useful to describe the section of the program.

Example:

O0001;

(Main program for part 29665688-Pilatus);

N1;

T0101;

(Rough turning TCGX102-AL804);

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You are aware that sub programs are useful for repeating the same

operation.

Custom macro function allows use of variables,arithmetic and

logical operations and conditional branches for easy development

of general programs.

It is useful to develop custom designed canned cycles.

They are very useful in generating alarms under stated conditions.

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A macro variable is always prefixed with a

symbol.

Example : #100

Arithmetic expressions can be used to storethe values into macro variable.

Example #100 = #112-12;

Types of variables

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Types of variables

Null variable #0 is always represents a zero;

Local variables #1 to #33 are temporary locations to storeresults. Volatile.

Common variables #100 - #199 they can be shared amongmany programs. Volatile.

Common variables #500-#999 are common variables. Non-Volatile.

#1000System variables used to read and write NC dataitems like pallet in work zone, tool number, axis current

position etc.,

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Variable values-1047to -10-29

0

10-29to 1047

Referencing the variables in a part program.

N1 G01 X#500 F#501;

N2 S#503;

Macro alarms

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Macro alarms

We can build our own alarms using macro

#3000=1(TOOL OFFSET WRONG);

Will stop the machine and display an alarm in the screen

3001 TOOL OFFSET WRONG

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The current position of each axis is available in a macro

#5021 gives the machine current position for X

#5022 gives the machine current position for Y

#5081 and #5082 gives tool offset value.

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Arithmetic operations

Sum,Difference,Product and Quotient can be performed.

For example

#500 = #500+1;

Trigonometric and logarithmic operations

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g g p

#I=SIN [#j];

#I=COS [#j];

#I=TAN [#j];

#I=SQRT [#j];

#I=ABS [#j];

#i=LN [#j];

#I=EXP [#j];

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Conditional branch

IF [#100 GT 10] GOTO 2;

EQ = EQUAL TONE= NOT EQUAL TO

GT= GREATER THAN

GE= GREATER THAN OR EQUAL

LT= LESS THAN

LE= LESS THAN OR EQUAL

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BRANCHING EXAMPLE

O0003;

IF[#530 NE 5142] GOTO7;

.

.

.

.

.

.

N7;

IF[#501GT5000]#3000=1(TOOL LIFE END);

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WHILE STATEMENT

WHILE [conditional expression] DO m;

End m;

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G CODE INFORMATION

The present value of a modal G code can be

read from a macro variable.

If the machine is in G00 mode then #4001=00

G01 #4001=01

G02 #4002=02

G03 #4002=03

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Thank you