Programming Systems | CNC programming Basics | G-Code | M-Code | Incremental and Absolute Programming System | Interpolation | Linear Interpolation | Circular Interpolation

Interpolation
The method by which contouring machine tools move from one programmed point to the next is called interpolation. This ability to merge individual axis points into a predefined tool path is built into most of today’s MCUs.


There are five methods of interpolation:

  • linear

  • circular

  • helical

  • parabolic

  • cubic

All contouring controls provide linear interpolation, and most controls are capable of both
linear and circular interpolation. Helical, parabolic, and cubic interpolation are used by industries that manufacture parts which have complex shapes, such as aerospace parts and dies for car bodies.


Linear Interpolation


Linear Interpolation consists of any programmed points linked together by straight lines, whether the points are close together or far apart

Curves can be produced with linear interpolation by breaking them into short, straight-line segments. This method has limitations, because a very large number of points would have to be programmed to describe the curve in order to produce a contour shape. A contour programmed in linear interpolation requires the coordinate positions (XY positions in two-axis work) for the start and finish of each line segment. Therefore, the end point of one line or segment becomes the start point for the next segment, and so on, throughout the entire program.


01-example of Linear Interpolation-straight line motion of a cutter-2 axis-2 position


Circular Interpolation


The development of MCUs capable of circular interpolation has greatly simplified the process of programming arcs and circles. To program an arc, the MCU requires only the coordinate positions (the XY axes) of the circle center, the radius of the circle, the start point and end point of the arc being cut, and the direction in which the arc is to be cut (clockwise or counterclockwise)


01-circular Interpolation


Codes:


The most common codes used when programming CNC machines tools are

  • G-codes (preparatory functions), and

  • M codes (miscellaneous functions).

Other codes such as F, S, D, and T are used for machine functions such as feed, speed, cutter diameter offset, tool number, etc.



G-Code


G-codes are sometimes called cycle codes because they refer to some action occurring on the X, Y, and/or Z axis of a machine tool.


01-G-Codes example-rapid transverse-Linear Interpolation-Straight line path

01-G-Codes-Circular Interpolation colockwise-Anticlockwise or Counterclockwise

GroupCodeFunction
01G00Rapid Positioning
01G01Linear Interpolation
01G02Circular Interpolation  clockwise (CW)
01G03Circular Interpolation Counter clockwise (CCW)
06G20*Inch input (in.)
06G21*Metric Input (mm)
G24Radius Programming (**)
00G28Return to Reference Point
00G29Return from Reference Point
G32Thread Cutting (**)
07G40Cutter Compensation Cancel
07G41Cutter Compensation Left
07G42Cutter Compensation Right
08G43Tool length compensation positive
08G44Tool length compensation minus
08G49Tool Length Compensation Cancel
G84Canned Turning Cycle (**)
03G90Absolute Programming
03G91Incremental Programming
(*) – on some machines and controls, these may be G70 (inch) and G71 (metric)
(**) – refers only to CNC lathes and turning centers.


M-CODE:


M or miscellaneous codes are used to either turn ON or OFF different functions which control certain machine tool operations.


01-M-Codes-Direction of Rotation-Clockwise-Counter clockwise-Tool Change - End of program-return to beginning



Code     Function

M00     Program stop
M02     End of program
M03     Spindle start (forward CW)
M04     Spindle start (reverse CCW)
M05     Spindle stop
M06     Tool change
M08     Coolant on
M09     Coolant off
M10     Chuck – clamping (**)
M11     Chuck – unclamping (**)
M12     Tailstock spindle out (**)
M13     Tailstock spindle in (**)
M17     Tool post rotation normal (**)
M18     Tool post rotation reverse (**)
M30     End of tape and rewind
M98     Transfer to subprogram
M99     End of subprogram
(**) – refers only to CNC lathes and turning centers.
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