Preparatory Function: This information is given by word, which is prefixed by letter G followed by numerical code for the operation for which the control unit is to instruct machine tool. For example, G03 means the instruction for Circular Interpolation in Counter Clock Wise (CCW) direction. The other parameters necessary for carrying out the operation will follow. The word G will not be able to operate the machine tool till all relevant information, which follows is processed.
|
Code |
Function |
|
G00 |
Point
to point positioning |
|
G01 |
Linear
Interpolation |
|
G02 |
Circular
Interpolation (Clock Wise –normal dimension) |
|
G03 |
Circular
Interpolation (Counter Clock Wise-normal dimension) |
|
G04 |
Dwell |
|
G05 |
Hold |
|
G08 |
Acceleration |
|
G09 |
Deceleration |
|
G10 |
Linear
Interpolation (Long Dimension) |
|
G11 |
Linear
Interpolation (Short Dimension) |
|
G12 |
3D
Interpolation |
|
G13-G16 |
Axis
Selection |
|
G17 |
XY
Plane Selection |
|
G18 |
ZX
Plane Selection |
|
G19 |
YZ
Plane Selection |
|
G20 |
Circular
Interpolation Arc CW (Long Dimension) |
|
G21 |
Circular
Interpolation Arc CW (Short Dimension) |
|
G25 |
Start
of Subroutine |
|
G26 |
End
of Subroutine |
|
G28 |
Return
to Home Position |
|
G30 |
Circular
Interpolation Arc CCW (Long Dimension) |
|
G31 |
Circular
Interpolation Arc CCW (Short Dimension) |
|
G33 |
Thread
Cutting Constant Lead |
|
G34 |
Thread
Cutting, Increasing Lead |
|
G35 |
Thread
Cutting, Decreasing Lead |
|
G40 |
Cutter
Compensation Cancel |
|
G41 |
Cutter
Compensation Left |
|
G42 |
Cutter
Compensation Right |
|
G43 |
Cutter
Compensation Positive |
|
G44 |
Cutter
Compensation Negative |
|
G53 |
Linear
Shift Cancel |
|
G54 |
Linear
Shift X |
|
G55 |
Linear
Shift Y |
|
G56 |
Linear
Shift Z |
|
G57
|
Linear
Shift XY |
|
G58 |
Linear
Shift XZ |
|
G59 |
Linear
Shift YZ |
|
G62 |
Positioning
Fast |
|
G63 |
Tapping |
|
G64 |
Change
of Rate |
|
G78,
G79 |
Milling
Cycle |
|
G81 |
Drilling
cycle |
|
G82 |
Drill
Dwelling Cycle |
|
G84 |
Tapping
Cycle |
|
G85 |
Reaming
Cycle |
|
G86 |
Boring
Cycle |
|
G80 |
Fixed
Cycle Cancel |
|
G90 |
Absolute
Coordinate |
|
G91 |
Incremental
Coordinate |
|
G92 |
Work
Shift |
|
G94 |
Feed
Per Minute |
|
G95 |
Feed
Per Revolution |
|
G96 |
Spindle
RPM |
|
G98 |
Return
To Initial Level |
|
G99 |
Return
To Retract Plane |
Absolute
& Incremental Preparatory Functions:
Preparatory
function G 90 means that the data in the following block is in absolute mode
(relative to common datum) and G91 means the data is in incremental mode
(relative to current position). G90 can be cancelled by G91 or vice versa.
Canned Cycles
In many of machining operations, some preliminary movements are required before actual machining starts. Let us take the example of drilling operation: the tool has to first approach the position of actual drilling, then the tool will move down till it is close to work surface and it starts to move down into the work piece with instructed feed rate. After the hole has been drilled the tool will retract to a position above the work piece. Same sequence of motions will be followed by the tool for drilling another hole. It will be more precise if the sequence of tool motions related to a particular operation can be addressed by certain preparatory functions. This purpose is served by canned cycles (packed cycles).
Let us take an example of one such canned cycle: G81 (drilling cycle). This cycle starts with rapid movement in X or Y direction to position the work below the tool spindle, then rapid motion takes place in Z direction up to a plane 1-2 mm above the surface of the work. Such plane just above the work surface is called R-plane. Then further motion takes place in Z direction and into the work till the required depth is obtained. After that the tool rapidly retracts to R –plane. And the cycle completes.
G82
for dwell cycle is similar to G81 except that the tool dwells for an
amount of time pre-selected when full
Z-depth is achieved.
G80
for canceling cycle:
All cycles mentioned above would continuously take place again and again at newer coordinate positions given. This saves a lot of time in programming, tape preparation and reading of tape. However if the cycle in operation has to be terminated a preparatory code G80 is necessary to be given. The statement for termination of a canned cycle in effect would look like
N__ G80 Z0 F0 M05 *
The
R-Plane:
The R-plane refers to the rapid plane, which is kept 1-2 mm above the surface of the part since all the operations prior to actual machining and reaching R plane and also tool retraction (after the operation0 up to R plane take lace at the highest feed rate possible on the machine.