25 CNC programming.pdf

Information Needed by a CNC

Machine

CNC Programming

1. Preparatory Information: units, incremental or

absolute positioning

2. Coordinates: X,Y,Z, RX,RY,RZ

3. Machining Parameters: Feed rate and spindle

speed

4. Coolant Control: On/Off, Flood, Mist

5. Tool Control: Tool and tool parameters

6. Cycle Functions: Type of action required

7. Miscellaneous Control: Spindle on/off, direction

of rotation, stops for part movement

Lecture 25

Engineering 475

Automated Production Systems

This information is conveyed to the machine through a set

of instructions arranged in a desired sequence – Program .

Cartesian Coordinate Systems

Right Hand Rule

Consists of three axes positioned 90

degrees from each other.

Chang, Fig. 10.1

The right hand rule is used to define the

positive direction of the coordinate axes.

Nanfara, Fig. 2.1

Standard Lathe

Coordinate System

Gantry Mill Coordinate

System

Coordinate System

System

Nanfara, Fig. 2-4

Nanfara, Fig. 2-3

Information Needed by a CNC

Lecture 25

Engineering 475

Standard Lathe

Gantry Mill Coordinate

Vertical Mill or Drill

Coordinate System

Milling Tool Coordinate System

Coordinate System

Chang, Fig. 10.3

Nanfaro, Fig. 2-6(b)

Cartesian Coordinate

System Planes

Absolute Coordinates

X-Y Plane

X-Z Plane

Y-Z Plane

Nanfaro, Fig. 2-7

Nanfaro, Fig. 2-10

Incremental Coordinates

Coordinate System Exercise

Nanfaro, Fig. 2-11

Vertical Mill or Drill

Cartesian Coordinate

System Planes

Letter Codes

(G and M Codes)

Example CNC Program

• Each instruction to the machine

consists of a letter followed by

a number.

Example CNC Program

• G-codes : Preparatory Functions

– involve actual tool moves.

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

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

• Each letter is associated with a

specific type of action or piece

of information needed by the

machine.

• M-codes : Miscellaneous

Functions – involve actions

necessary for machining (i.e.

spindle on/off, coolant on/off).

Letters used in Codes

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

Letter Codes

(G Codes)

Letter Codes

(M Codes)

G00

Rapid traverse

G40 Cutter compensation – cancel

G41 Cutter compensation – left

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

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

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

Absolute dimensions

G20

Inch Units (G70)

G91

Incremental dimensions

G21

Metric Units (G71)

Letter Codes

(N Codes)

Letter Codes

(X,Y, and Z Codes)

(N Codes)

(X,Y, and Z Codes)

Example CNC Program

• N-codes : Gives an

identifying number for each

block of information.

• X, Y, and Z codes are used to

specify the coordinate axis.

• Number following the code

defines the coordinate at the end

of the move relative to an

incremental or absolute

reference point.

• The number may require that a

specific format be used (i.e. 3.4

means three numbers before

the decimal and four numbers

after the decimal).

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

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

It is generally good practice to

increment each block number by

5 or 10 to allow additional

blocks to be inserted if future

changes are required.

Letter Codes

Letter Codes

(I,J, and K Codes)

Letter Codes

(F, S, and T Codes)

(I,J, and K Codes)

(F, S, and T Codes)

Example CNC Program

• I, J, and K codes are used to

specify the coordinate axis

when defining the center of a

circle.

• Number following the code

defines the respective coordinate

for the center of the circle.

• The number may require that a

specific format be used (i.e. 3.4

means three numbers before

the decimal and four numbers

after the decimal).

Example CNC Program

F-code : used to specify the feed

rate

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

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

S-code : used to specify the

spindle speed

T-code : used to specify the tool

identification number associated

with the tool to be used in

subsequent operations.

Letter Codes

(R and P Codes)

Program Start Flag and Program

Identification Number

(R and P Codes)

Example CNC Program

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

R-code :

•Retract distance when used with

G81, 82, and 83.

•Radius when used with G02 and

G03.

Example CNC Program

:1045

N5 G90 G20

N10 M06 T3

N15 M03 S1250

N20 G00 X1 Y1

N25 Z0.1

N30 G01 Z-0.125 F5

Program start flag. Placed at

the beginning of each program.

:1025 Program identification number.

Follows the program start flag

at the beginning of each

program.

P-code : Used to specify the

dwell time associated with

G04.

Only two commands that

don’t start with a letter.

Three Major Phases of a CNC

Program

Three Major Phases of a CNC

Program

Phase 1 - Program Setup

Program Setup

Phase 2 – Material Removal

Material Removal

(Program start flag)

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

N25 Z0.125 (Rapid down to Z0.125)

N30 G01 Z-0.125 F5 (Feed down to Z-0.125 at 5 ipm)

N35 G01 X2 Y2

:1001

(Four digit program number)

N5 G90 G20

(Absolute units, inches)

(Feed diagonally to X2,Y2)

N10 M06 T2

(Stop for tool change, use tool # 2)

N40 G00 Z1

(Rapid up to Z1)

N15 M03 S1200

(Turn the spindle on CW to 1200 rpm)

N45 X0 Y0

(Rapid to X0,Y0)

Nanfara, pg. 36

Letter Codes

Program Start Flag and Program

Letter Codes

Three Major Phases of a CNC

Phase 1

Phase 2

Three Major Phases of a CNC

Program

Block Format

Program

Sample Block

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

Phase 3 – System Shutdown

System Shutdown

• 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 (on separate lines)

• The data within a block should follow the sequence shown

in the above sample block

N50 M05

(Turn the spindle off)

N55 M30

(End of program)

Nanfara, pg. 36

Modal G- Codes

Codes

Modal G- Code List

Code List

Example CNC Program

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

G43

Tool length compensation (plus)

Most G-codes set the

machine in a “mode”

which stays in effect

until it is changed or

cancelled by another G-

code. These commands

are called “modal”.

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

G44

Tool length compensation (minus)

G49

Tool length compensation cancel

G80

Cancel canned cycles

G81

Drilling cycle

G82

Counter boring cycle

Cutter compensation cancel

G83

Deep hole drilling cycle

G41

Cutter compensation left

In the example, G00 and

G01 are modal.

G42

Cutter compensation right

G90

Absolute positioning

G43

Tool length compensation (plus)

G91

Incremental positioning

Assignment

Review the material presented.

Next class we look at an example,

and will develop G-code programs

in class.

Three Major Phases of a CNC

Phase 3

Modal G

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