1. Unit -5
CNC MACHINE
TOOLS AND PART
PROGRAMMING

2. History of CNC
• .

3. INTRODUCTION
• In 1940 Mr.T.Parson
develops a numerical co-
ordinate system to control the
machines.
• He uses card reader and
tape reader to feed the data

4. .
• In 1949, he demonstrate his NC machine
and its concept in U.S.Airforce.
• Then it was taken as a series of research project
at the servo mechanism laboratory of the
Massachutts Institute of Technology (MIT)

5. .
• In 1952, the first demo of prototype was held.
• So the usefulness of NC machine proven
• This initiate the commercial use of NC machine
for production in industry.

6. .
• Then the series of improvement involves
in the change of part programming.
• APT – Automated Programming tool
language developed.
• This become a base to other languages

7. Limitations in NC machine
1. Part programming mistakes
2. Punched card wear and tear
3. Punched tape wear and tear
4. Lack of speed and feed
5. Least reliability
6. Poor data communication

8. ,
• In 1968, DNC –direct numerical control
developed.
• This machine eliminates the previous NC
machine Problems.
• Using the common computer control system, all
the NC machines are controlled
• But the cost and size of the computer is more

9. .
• In 1970, CNC –computer numerical control
• A small less expensive computers are
attached to the machine body to control its
operations.

10. Mechanical Engineering Department 10
Numerical Control
• Numerical control is a method of
automatically operating a manufacturing
machine based on a code of letters, numbers,
and special characters.
• The numerical data required to produce a
part is provided to a machine in the form of a
program, called part program or CNC
program.
• The program is translated into the appropriate
electrical signals for input to motors that run
the machine.

11. NC SYSTEM

12. NC
• .

13. Mechanical Engineering Department 13
Hardware Configuration of NC Machine
Machine Control Unit (MCU)
the brain of the NC machine.
The Data Processing Unit (DPU)
reads the part program.
The Control Loop Unit (CLU)
controls the machine tool operation.

14. Types of NC system
1.Point to point NC system
2.Straight cut NC system
3.Contouring NC system

15. Mechanical Engineering Department 15
1.Point-to-Point Tool Movements
Point-to-point control systems cause the tool to move to a point on the
part and execute an operation at that point only. The tool is not in
continuous contact with the part while it is moving.
Drilling, reaming, punching, boring and tapping
are examples of point-to-point operations.

16. 2.Straight cut method NC system
Here the cutting tool moving parallel to one of the
major axes at a controlled rate for machining.
Its preferred for milling operations.
So only one axis of tool movement.
Angular cuts are not preferred.

17. Mechanical Engineering Department 17
3.Continuous-Path Tool Movements
Continuous-path controllers cause the tool to maintain continuous contact
with the part as the tool cuts a contour shape. These operations include milling
along any lines at any angle, milling arcs and lathe turning.

18. Mechanical Engineering Department 18
Hardware Configuration of NC Machine
Machine Control Unit (MCU)
the brain of the NC machine.
The Data Processing Unit (DPU)
reads the part program.
The Control Loop Unit (CLU)
controls the machine tool operation.

19. Co – Ordinate system in NC
system
• Depend on the
machining to be
done, the axes are
selected.

20. Advantages NC over traditional
machine
• Tool operation by hand is minimized by
part programming.
• A ready made set of data card or tape is
used for machining at any time.
• Semi – skilled labors are enough
• Worker fatigue minimized.
• Complex shapes are machined easily.
• But Need programming knowledge

21. CNC
COMPUTER NUMERICAL
CONTROL

22. CNC
• The CNC having the same operation as that of
NC.
• The only difference is the usage of computer.
• The part program is stored in the inbuilt
computer.
• So when ever the machining needed or altered
, they have simply altered the saved program
Mechanical Engineering
Department

23. Configuration in CNC

24. CNC
COMPUTER NUMERICAL
CONTROL

25. Mechanical Engineering Department 25
HAAS CNC Machines

26. Mechanical Engineering Department 26
CNC Machines
Machining Centers, equipped with automatic tool changers, are capable
of changing 90 or more tools. Can perform milling, drilling, tapping,
boring… on many faces.

27. Mechanical Engineering Department 27
CNC Machines
Turning Centers are capable of executing many different types of lathe
cutting operations simultaneously on a rotating part.

28. Mechanical Engineering Department 28
CNC Controllers
The NC controller is the brain of the NC system, it controls all functions of
the machine.
• Motion control deals with the tool position, orientation
and speed.
• Auxiliary control deals with spindle rpm, tool change, fixture
clamping and coolant.
Many different types of controllers are available in the market (GE,
Fanuc, Allen-Bradley, Okuma, Bendix, …).
There are two basic types of control systems:
point-to-point and continuous path.

29. Advantages of CNC over NC
• Flexibility in changing the part program
• Storage facility
• Card reader , tape reader errors
minimized.
• More suitable for mass production
• System also flexible.
• Very less manual work

30. DNC
Direct Numerical Control

31. DNC
• Here number of NC machines are controlled by a
common central computer.
• From the bulk memory storage the data send to
individual machines.
• It also receive the feed back.
• The two way information flow occurs in real time between
central computer and individual machine tools.

32. Difference between
CNC and DNC
• CNC can do operations on only one
machine at a time.
• But DNC involves doing different
operations in number of NC machines by
using only one central computer.

33. Machining centers
• .

34. Machining centers
• Its one of the important type of CNC machine
tools.
• Automatic tool changer (ATC) used.
• Milling, drilling, reaming, boring, tapping
operations are carried out.
• Indexing tool changer is the specialty of this
center. (having 60 – 100 tool)
• Automatic pallet changer is used and time will be
reduced

35. classification
• Horizontal spindle machining center
• Vertical spindle
• Universal center

36. Horizontal center

37. Vertical center

38. Universal center
• Single spindle
• Combination of both vertical and horizontal
machining center.

39. .
DRIVE SYSTEM

40. Basic systems
The NC and CNC machines are divided
into two groups.
1. Electromechanical devices
2. Digital Circuits
The drives are hydraulic actuators, DC motors
or stepping motors.

41. AC DRIVES
• Now a days the CNC manufacturers avoiding the
use of DC motors.
• Due to the brush maintenance problem they go
for using AC Drives

42. Principle of operation
• The velocity of the AC synchromotor is controlled
by manipulation of the voltage frequency supplied
to the motor.
• The frequency manipulation requires the use of
an electrical inverter.
• The inverter convert the DC to AC voltage with a
continuous controllable frequency

43. Advantages of AC over DC motor
• Ac motors are more reliable than DC
• AC motors provides stable and smooth drive
• AC cooling system allows high speed , high
output with compact size
• AC motors are free from brushes which avoid
maintenance
DIS-ADVANTAGE
• Inverter cost and size is more

44. .
DC MOTORS

45. DC MOTORS
• This is most widely used in controlling all
small , medium sized NC and robot system
drives
• It gives a fine speed control in all operating
ranges of voltage given to the motor.
• This is also used in the drives of spindles in
lathe and milling machines.

46. Principle of DC motors
• This DC motor is actually a DC machine function either as motor or
as generator
• Its operation based on the rotation of an armature winding with in a
magnetic field.
• Armature – Rotor Field winding – Stator
The armature winding is connected to a commutator which is a
cylinder of insulated copper segments mounted on the rotor
shaft.
• Carbon brush is connected to the machine terminal are held against
the commutator surface to transfer DC current

47. Constructional Features of
CNC Machine Tool
• Some of the important parts of CNC machines tool are as follows:
(a) Machine structure,
(b) Slideways or guideways,
(e) Spindle / spindle bearings
1) Hydrodynamic
2) Hydrostatic
3) Antifriction
(d) Spindle drives
1) Electrical drives
2) Hydraulic drives
3) Pneumatic drives
(e) Feed drives
1) Servo motor
2) Mechanical transmission system
(f) Measuring systems
1) Direct
2) Indirect
(g) Controls, software and user interface
(h) Gauging
(i) Tool monitoring systems
1) Direct
2) Indirect.

48. Slideways Used in CNC
Machine Tools
Precise positioning and repeatability of
machine tool slides are the major
functional requirements of CNC machines.
The inaccuracies are mainly due to the
stick-slip motion when the plain (metal to
metal contact) slideways are used.

49. Requirement of a good slideway system:
A good slideway system must possess the
following functions.
1. Low coefficient of friction at varying slide
velocities.
2. Minimum difference between static and
dynamic friction coefficient – positiveslope
for friction - velocity characteristics.
3. Low rate of wear.
4. High stiffness at the sliding joints.
5. Sufficient damping.

50. Types of slideways used in CNC
machines:
1. Hydrostatic slideways
(i) Oil lubricated slideways
(ii) Air bearing slideways.
2. Anti-friction slideways
(i) Ball bearing slideways
(ii) Roller bearing slideways
(iii) Wear-resistant slideways.

51. Linear bearings with ball /
roller:

52. Wear-resistant recirculating ball
screw/Power screw:

53. Spindle Drives in CNC
Machines:
• The spindle drives are used to provide angular motion to the workpiece or a
cutting tool.
• Spindle drives are used to provide the main spindle power for cutting.
• As large material removal rates are used in CNC, large power motors are
used for spindle drives.
• Also, the speed required during operations is infinitely variable.
• Hence to provide such a speed control for infinitely variable speed DC
motors are used.
• The speed control for DC motors can be achieved by varying the voltage
infinitely
• The use of AC motors are preffered in the generation of currents in CNC
machine tools. This is achieved by developments in the frequency
converter.

54. Feed drives:
• CNC machines are provided with independent
axis drive to provide the feed movements for the
slides.
• In order to obtain fast response and positional
accuracy a special type of motor called
servomotor is used to power the slides.
• Following are the feed drives that are used in the
CNC machine tools :
i) DC servomotors ii) Brushless DC
servomotors iii) AC servomotor iv)
Stepper motor v) Linear motor

55. Compensations for Machine Accuracy
• Machine accuracy is the accuracy of the movement of
the carriage and it is influenced by
(i) Geometric accuracy in the alignment of the slide ways
(ii) Deflection of the bed due to load
(iii) Temperature gradients on the machine
(iv) Accuracy of the screw thread of any drive screw and
the amount of backlash(lost motion)
(v) Amount of twist (wind up) of the shaft which will
influence the measurement of rotary transducers

56. • Lead screw pitch error compensation
• Backlash compensation
• Sag compensation
• Tool nose compensation
• Cutter diameter
compensation
The CNC systems offer compensation for the various machines
accuracy. These are detailed below:

57. PART PROGRAMMING FUNDAMENTALS

58. Part Program

59. Methods of Creating Part
Programming
(i) Manual part programming.
(ii) Computer-assisted part programming
(CAD/CAM based programming system).
(iii) Manual data input
(iv) NC programming using CAD/CAM
(v) Computer automated part programming.

60. MANUAL PART PROGRAMMING
To be able to create a part program manually, it needs the following
information:
(a) Knowledge about various manufacturing processes and machines.
(b) Sequence of operations to be performed for a given component.
(c) Knowledge of the selection of cutting parameters.
(d) Editing the part program according to the design changes.
(e) Knowledge about the codes and functions used in part programs.

61. Function Address
Sequence number N
Preparatory function G
Coordinate word X, Y, Z
Parameters for Circular Interpolation I, J, K
Feed function F
Spindle function S
Tool function T
Miscellaneous function M

62. Preparatory Function(G)
 Preparatory commands which prepare the machine
or tool for differ modes of movement like positioning
countering, thread cutting and also preceeed the
dimension word. They are grouped .
 group cannot affect each other. only one function
from the same group can be at the same time.
 The preparatory functions and their codes used are
given in below.

63. • G00 point to point postioning
• G01 Linear interpolation
• G02 Circular interpolation
clockwise
• G03 Circular interpolation
anticlockwise
• G04 Dwell
• G06 Parabolic interpolation
• G08 Acceleration
• G09 Decealeration
• G17 XY plane selection
• G18 XZ plane selection
• G19 YZ plane selection
• G29 unassigned
• G33 Tread cutting, constant lead
• G34 thread cutting, increasing
lead
• G35 tread cutting decreasing lead
• G39 Unassigned
• G40 Tool offset cancel
• G42 Tool offset
• G59 Linear shift
• G60 Fine postioning
• G61 Medium postioning
• G62 Coarse postioning
• G63 Tapping
• G70 Inch programming
• G71Metric(mm)
• G80 Canned cycle cancel

64. Miscellaneous Function(M)
The function not relating the
dimensional movement of the machine
but denotes the auxiliary or switching
information is called as miscellenous
function for example are given below
M00 Programmed stop

65. • M00 Programmed stop
• M01 Optional Stop
• M02 End of program without skip
back
• M03 Spindle clockwise
• M04 Spindle anticlockwise
• M05 Spindle stop
• M06 Tool change
• M07 High pressure coolant ON
• M08 Low pressure coolant ON
• M09 Coolant OFF
• M10 Clamp workpiece
• M11 Release workpiece
• M12 Hydralic power rotatry table ON
• M13 Latreplacemnrt tool
• M14 Oil hole frill coolant ON
• M16 Heavy tool change
• M17 Tap cycle confirmation
• M18 Tap cycle cancel
• M19 Spindle orientation
• M20 Coolant nozzle up
• M21 Coolant nozzle middle
• M22 Coolant nozzle down
• M23 Detection of coolant in –X
• M24 Detection of coolant in+X
• M25 Detection of coolant in –Y
• M26 Detection of coolant in +Y
• M27 Tool breakage detection
• M28 Quill forward
• M29 Quill back
• M30 End of program with skip back

66. Co-ordinate System Group,
G90 and G91
• G90 Absolute
• N007 G90 G01 X5.0 Y10.0 F...
• N008 X25.0 Y15.0
• N009 X35.0 Y5.0
• G91 Incremental
• N007 G91 X5.0 Y10.0 F...
• N008 X20.0 Y5.0
• N009 X10.0 Y-10.0

67. Active Plane Selection Group, G17, G18, G19

68. N015 G92 X-150.0 Y200.0 Z50.0
Setting the work piece on the machine table
Preset, G92

69. Rapid Positioning, G00
N105 G90 G00 X150.0 Y30.0

70. Circular Interpolation, G02/G03
• F to G in XY plane, the program block would be,
as per ISO,
N125 G02 X65.0 Y60.0 I35.0 J-10.0 F250
• G to F, then it would be
N130 G03 X15.0 Y30.0 I-15.0 J-40.0 F250

71. Tool Length Compensation
• N003 M06 T01
• N006 M06 T02

72. Cutter Radius Compensation
G40 Compensation ‘off’.
G41 Used when the
cutter is on the left
G42 used when the cutter
is on the right

73. Automatically Programmed Tools
APT is a language of computer assisted part programming
for CNC machine tools. In this case, the programmer gives
instruction to the computer in the form of programming
language.

74. Structure of APT
Symbol Name Description
/ Slash
It divides a statement. Major words are at the left
of slash while minor words, symbols modifying the
words are on the right side. example : Go/To, L6
, Comma It is used as a separator between various
elements. Normally, it is on right side of slash.
= Equal to It is used to assign an entity to a symbolic name.
Example : SP = POINT / 80, 30, 50
( ) Parenthesis These are used to enclose the nested definitions.
$ Dollar It is placed at the end of line. This indicates that
the statement continues in next line.
$ $ Double Dollar Any statement after this sign is comment. It is not a part of
program

75. Mathematical Operations in APT
Symbol Operation Symbol Operation
+ Addition - Subtraction
* Multiplication / Division
** Exponential ABS Absolute value
SQRT Square root SIN Sin of angle
COS Cosine of angle TAN Tangent of angle
EXP Value of e to the power LOG Natural log

76. ADDITIVE MANUFACTURING
• Additive manufacturing is the formalized term for what used to
be called rapid prototyping and what is popularly called 3D
Printing.
• The term rapid prototyping (RP) is used in a variety of
industries to describe a process for rapidly creating a system
or part representation before final release or
commercialization.

77. Stages of AM process

78. Benefits of AM
• The speed advantage is not just in terms of the time it takes to build
parts. The speeding up of the whole product development process
relies much on the fact that we are using computers throughout.
• Since 3D CAD is being used as the starting point and the transfer to
AM is relatively seamless, there is much less concern over data
conversion or interpretation of the design intent.
• The seamlessness can also be seen in terms of the reduction in
process steps. Regardless of the complexity of parts to be built,
building within an AM machine is generally performed in a single step.
• Even a relatively simple change in the design may result in a
significant increase in the time required to build using conventional
methods.
• AM can, therefore, be seen as a way to more effectively predict the
amount of time to fabricate models, regardless of what changes may
be implemented during this formative stage of the product
development.

79. Features that represent problems using
CNC machining