CNC machine programming

1. Manufacturing Processes
CNC part programming

2. How CNC machine performs an operation on the work
piece?
To perform an operation we have to write a Part Program
which can be prepared manually(generally for small
programs) or automatically prepared(for complex
geometrical shapes) with the help of software packages.
The program need to specify:
- Which tool should be loaded on the machine spindle?
- What are the cutting conditions (speed, feed, coolant ON/OFF etc.)?
- What is the start point and end point of a motion segment?
- How to move the tool with respect to a work piece in a machine?

3. Program Structure

4.  The CNC machine receives a series of commands via CNC program through the
machine control.
 These commands are structured using letters and numbers such as G00 and S2300.
 There are some code differences between the various machine tool and control
manufactures.
 Each machine and control manufacturer provides a specific manual listing all the
commands.
 Most letter address codes fall into two categories: modal or non modal.
 Non modal codes are command codes that are only active in the block in
which they are specified and executed.
 Modal codes are command codes that once executed will remain active
throughout the program until another code in the same group overrides or
cancel it.

5. Address

6. Preparatory Function (G Address)

13. Basic codes and terms used are:
o Preparatory Codes (G ) for initial machining setup and
operating conditions.
o Miscellaneous Codes ( M) for on/off of coolant flow, spindle
rotation etc.
o Spindle Speed (S)
o Feed Rate (F)
o Tool number (T)

17. Cutting speed (SFM) and spindle speed (RPM) for hole
operation:
 The cutting speed is defined as the speed of any point on the
circumference of the cutter.
 It is usually expressed in surface feet per minute ( SFM).
 The tool speed and cutter diameter selected will be used to
calculate the spindle RPM.
 The cutting speed (SFM) selected for a particular hole operation will
depend on:
o Type of hole operation
o Material type
o Material hardness
o Hole depth
o Type of tool to be used
o Type of coolant system used
o Rigidity of the tool

18.  For reaming the cutting speeds ( SFM) are approximately one-half of what
is used for drilling.
 The cutting speeds (SFM) for tapping are usually much slower than for
drilling.
 Counter boring and countersinking speeds are approximately one-forth f
what is used for drilling.
 The cutting speeds of boring are approximately five times faster than for
drilling.
 For a drilling operation of mild steel plate:
o Part material is mild steel.
o Drill diameter is 0.750 inch
o Drill material is HSS.
o Choose cutting speed (CS), say 80 SFM
o RPM= ( 4 x CS)/ DIA = (4 x 80)/0.75 = 427 RPM
Cutting speed (SFM) and spindle speed (RPM) for hole
operation:

19. Tool Feed rate (IPR and IPM)for hole operations:
 The tool feed rate for hole operation (IPR) is defined as the amount (
inches) at which the tool advances into the work per one revolution.
 IPM= IPR x RPM ( of spindle).

20. • Tool speed ( RPM) for milling operations:
o Part material is mild steel
o Use a 4 inch cutter with 6 inserts ( coated carbide).
o Choose cutting speed (CS), say 700 SFM.
o RPM= 4 x CS/ Dia
• Tool Feed rate ( IPM) for milling operations:
o The tool feed rate, which is expressed in IPM, is defined as the rate at which
the cutter advances into the work.
IPM=RPM x T x N
o RPM= speed of milling cutter.
o T=feed per tooth (FPT)
o N= number of inserts on the milling cutter.

22. Rapid Traverse and feed moves:
G00Rapid Movement:
o The G00 rapid code is primarily used to move the X-, Y-, or Z- axis as fast as
possible.
o Therefore, after the G00 code an axis or combination of axes follows.
o G00 code is modal and will remain active for each subsequent line until it
is canceled.
o Therefore, any axis letter present in a subsequent line of the CNC program
will move in rapid traverse mode whether the G00 code is present or not.
o The G00 code is canceled by either the G01, G02, or G03 code.

23. Rapid Positioning

24. G00 X- axis Rapid Traverse Description for VMC:

25. G00 Y- axis Rapid Traverse Description for VMC:

26. G00 Z- axis Rapid Traverse Description for VMC:

27. G00 X- axis Rapid Traverse Description for HMC:

28. G00 Y- axis Rapid Traverse Description for HMC:

29. G00 Z- axis Rapid Traverse Description for HMC:

30. G01 Feed Movement: (Linear Interpolation)
o The G01 feed code is primarily used to move the X-, Y-, Z- axis at a
predetermined feed rate to cut the work piece.
o For the G01 code a feed rate value is required.
o The G01 code and the F code are also modal and will remain active for
each subsequent line until they are changed or canceled.
o feed move are mainly executed for cutting the part material, and
therefore the spindle must be rotating prior to reading the G01 command
code.

31. Linear Interpolation

32. G01 X- axis Feed Move Description for VMC:

33. G01 Y- axis Feed Move Description for VMC:

34. G01 Z- axis Feed Move Description for VMC:

35. G28 Machine Home Return:
o The CNC machine must be homed in all axes ( X,Y, Z, and B for HMC) before
the CNC program can be cycled.
o The CNC machine axes can be homed manually with the control, or
automatically with the G28 code.

36. Part Programming
M03, M04 and S spindle function code:
o M03 code is used to rotate the spindle in a CW direction.
o M04 code is used to rotate the spindle in a CCW direction.
o To start the spindle rotation, the CNC program must read the S code
and RPM value. Either before or at the same time that the M code
is read.
o S1525 M03

37. M05 spindle stop code:
o The M05 code is used in situation when the spindle rotation needs to be
stopped during the automatic execution of the CNC program.
o The M05 spindle stop code is required in situations such as the following:
o Before tool changes
o To inspect a machines feature size.
o To remove machining metal chips
o To unload or load a workpiece
o To manually change a tool.
o There are also situations when the spindle rotation is stopped without an
M05 code. The spindle rotation is stopped internally by the MCU in
situations such as the following:
o When the emergency stop button is pressed.
o During the execution of an automatic tool change.
o During the execution of some canned cycles.

38. Circular Interpolation:
o Circular interpolation is used to cut circular features on a work piece.
o To perform circular interpolation basically requires a code ( G02 or G03),
the arc radius size, and the starting and ending coordinates of the arc.
o For CNC machining centers, circular interpolation is typically performed
using an end mill cutter to machine the work piece.

39. Circular Interpolation:

40. Circular Interpolation

41. Cutter Compensation

42. Cutter Compensation

43. Cutter Compensation

46. Program Example 1

48. CNC Turning Program

49. CNC Turning Program