This document provides an overview of computer numerical control (CNC) and programming. It discusses the history of NC machines from 1945 onwards. It then defines numerical control and describes how the control strategy is applied to machine tools like lathes and mills. The document outlines the advantages of CNC machining over conventional machining and lists some common applications. It also discusses elements of the NC system like data processing units, classification of systems, and CNC axes nomenclature. Finally, it provides a brief introduction to CNC programming concepts like workpiece and machine zero, G and M codes, programming methods like point-to-point and continuous path, and examples of simple CNC programs.

1. Computer Numerical Control and Programming
Dr. Mandeep Dhanda, PIED, PEC Chandigarh

2. 1945
▫ First digital electronic computer ENIAC
1952
▫ MIT demonstrated First NC Machine in laboratory
NC Development
▫ Direct Numerical Control DNC
▫ Computer Numerical Control CNC
▫ Distributed Numerical Control DNC
▫ Flexible Manufacturing System FMS
▫ Computer Integrated Manufacturing CIM
2
History of NC

3. 3
Numerical Control ?
A CONTROL Strategy
to
operate a machine tool
using
NUMBERS, LETTERS and SYMBOLS.

4. Control Strategy applied to various machine
tools.
• Lathe/Turning Centers
• Milling Centers – Simple/Complex 2-5 Axis
• Grinding
• EDM/Wire EDM
• Laser Cutting
• Tool Grinding
4
NC MachineTools

5. 5
Applications of CNC
CNC Plasma Cutter CNC Engraving
CNC Electric Discharge Machining CNC Milling

6. 6
Why CNC Machining ?
• For the parts
 having complex contours
 requiring very high accuracy and repeatability
 requiring many set-ups and/or the setups very
expensive
 subjected to frequent design changes, flexibility

7. • Reduction of Lead Time from Design to Mfg.
• Accurate machining of Complex surfaces/parts
• Excellent repeatability and Interchangeability
• Greater Machine utilization – scrap reduction
• Improved Productivity
• Quick Turn-around for design revisions, Prototyping
7
Advantages of NC Technology

8. 8
Elements of NC tool operation

9. Data Processing Unit & Control loop unit
Function
• Reading Program
• Decoding
• Data Computation
• Axis Control Data Creation
• Data transfer to motors, relays
• Feedback control of axes
• Machine control functions
9
Elements of NC tool operation

10. BS 3635
• Motion Control
▫ Point to Point p
▫ Paraxial- Straight Line L
▫ Continuous Path / Contouring C
• Capabilities
▫ No. of Axes controlled Simultaneously
▫ Interpolation
 Linear, Circular, Helical, Parabolic
• Axis Definition
• Machine Configurations
▫ 2-5 axis
10
Classification of CNC system

11. 11
Classification of NC system
NUMERICAL CONTROL
FINITE POSITIONING
CONTROLS
POINT TO POINT
SYSTEMS STRAIGHT CUT
SYSTEMS
CONTINUOUS PATH
SYSTEMS
CONTOURING
SYSTEMS
Ex. Drilling, Boring, Robotics Frame Milling, CNC Turning 2,3 axis contouring, SSM

12. • Moving at Maximum Feed rate from point to
point
• Accuracy of the destination is important but not
the path
• Drilling is a typical application
12
Point To Point - PTP

13. • Precise control of both the displacement and
velocity along the path (Both pos. and path
are important)
• Machining of profiles
• Uses Linear and Circular interpolators
13
Continuous Path Control

14. 14
2. Point-to-point(P-T-P) control is applicable in case of
(a) CNC drilling machine
Short Quiz
(b) CNC milling machine (c) CNC lathe (d) None of these
1. There is a stepper motor rotating at 20 rpm and is connected with a table through gear box, lead screw-nut
connection as shown in Fig. 1. The table has single axis of motion and is developing a speed of 20 mm/min
along that axis due to motor rotation. The stepper motor covers one rotation in 200 steps and moves one
step per pulse of the pulse generator. The Basic length unit (BLU) of the drive is (motion of table per pulse of
pulse generator) ?
(a) 0.01mm (b) 0.05mm (c) 0.1mm (d) 0.005mm (e) None of these
3. CNC machining has the following main advantage over conventional automated machining
(a) Ability to employ higher
cutting speed, feed, doc
(b) Flexibility (c) Feedback control (d) None of these
4. An interpolator is definitely present in
(a) A CNC P-T-P control machine (b) A CNC P-T-P control machine with feedback
(c) A CNC continuous control machine (d) All CNC machines
20 rpm 20mm/min
1rev 1mm
1/200 rev 0.005mm

15. CNC Axes Nomenclature and
Configuration
15

16. 16
CNC Axes Nomenclature
Linear : X, Y, Z (Primary)
U, V, W (Secondary)
P, Q, R (Tertiary)
Rotary : A, B, C
Control : Sequential
Simultaneous
Spindle axis is always Z

17. 17
CNC Axes Designation
Vertical axis Milling machine CNC turning center

18. Rotating and Tilting Head (B, C)
18
Rotating and Tilting Table (A,C) Rotating Table, Tilting Head (A,C)
5 Axes CNC Machine Configuration

19. 19
CNC 5 Axes Configuration
HMC with 5 axes-Rotary table
VMC with 5 axes-Tilting tool head

20. Turbine Blade - 5 axis CNC machining
https://www.youtube.com/watch?v=SNoj5XtpEa8
20
Video-5 axis CNC Machining
V8 Engine Block - 5 axis CNC machining
https://www.youtube.com/watch?v=wHstzxuryMk

21. CNC Programming
21

22. 22
CNC Program
1. Reading drawing
2. Programming
3. Inputting Program
4. Manufacturing
From the drawing to the workpiece

23. 23
Machine and Part Zero
• Each CNC machine has a built-in location that is called Machine zero.
• Before moving and cutting a block, the CNC machine needs to know where to start, the start
position is the part zero used in programming.
• This location acts as the origin from which all the other dimensions are calculated during the
program and it is usually located on the edge of a workpiece.

24. N010 G20 G40 G80 G90;
N020 S3000 M03;
• Program consists of BLOCKS.
• Each BLOCK has WORDS.
• Each WORD denotes ACTION.
• Program has to EXPLICITLY specify the
ACTION to be done by Tool/Machine.
24
CNC Program
M/c tool action:
• Feed the Tool. Start the Machine. Rotate Spindle.
• Clamp the Job.
• Start the Coolant.
• Stop the Machine.

25. 25
G00
RAPID TRAVERSE
G01
LINEAR INTERPOLATION
(STRAIGHT LINE MOVEMENT)
G02
CIRCULAR INTERPOLATION
(CLOCKWISE)
G03
CIRCULAR
INTERPOLATION
(COUNTERCLOCKWISE)
CNC Command G/M code
(Deckel Maho, Inc.)
G – Preparatory code

26. 26
M03
DIRECTION OF ROTATION
(CLOCKWISE)
M04
DIRECTION OF ROTATION
(COUNTERCLOCKWISE)
M06
TOOL CHANGE WITH
AUTOMATIC RETRACTION
M30
END OF PROGRAM
AND
RETURN TO BEGINNING
OF PROGRAM
Word Address Format
(Deckel Maho, Inc.)
M – Miscellaneous code
CNC Command G/M code

27. 27
(Kelmar Associates)
Absolute/Incremental Programming
G90- Absolute Programming G91- Incremental Programming

28. 28
Tool Path without Cutter Compensation Tool Path with Cutter Compensation
Cutter Compensation G41/42
G40- Cancel Cutter Compensation
Cutter Compensation: G41- Left
and G-42 Right

29. Part
Entry
Exit
Tool Path Stages
• Entry – RAMP ON
• Machining Profile
• Exit – RAMP OFF
29
When to start Compensation?

30. Point to Point (PTP) Programming
• Repetition – GOO, X, Y
• Modal Words - Create Compact Code
30
Programming

31. 31
15 Holes
8 Dia, 5 Deep
100
100
200
300
Plate: 400 X 200 X 25 mm
25
25
Example (PTP)

32. 32
-- -- -- --
N – G99 G81 X100 Y100 Z-5 R2 F50
N- M98 P300
N- X200 Y100
N- M98 P300
-- -- -- --
N- M30
:300
N10 G91 X25
N20 X-25 Y25
N30 X-25 Y-25
N40 X25 Y-25
N50 G90
N60 M99
25
25
CNC PTP Program, Subroutine
Absolute – G90
Incremental – G91
(X100 Y100)
100 100
100

33. 33
% O0001
---Initialization------(G90 G21 G40 G80)
---Zero Setting------(G92 X0 Y0 Z0)
-Tool Selection(M06T1),Spindle On(M03)
G41 G01 X0 Y-40.0 F 300
Y250.0
X200.0
G02 Y0 R125.0;
G01 X-40.0
G40 G00 X-100.0 Y100.0
-Spindle Stop(M05),Return Home(G28)
---Program Stop – (M30)
Part Program- Contouring

34. 34
• https://academy.titansofcnc.com/files/Fundamentals_of_CNC_Machining
• https://www.engr.uvic.ca/~mech410/CAM_references/CNC_Computer_Numerical_Control_Programmig_Basics
• CNC Programming Handbook (3rd edition) by Peter Smid
• Computer Numerical Control Simplified by Steve Krar and Arthur Gill
• CNC Programming Techniques by Peter Smid
• CNC Trade Secrets by James Harvey
• Programming of CNC Machines by Ken Evans
• Deckel Maho inc.
References