This document provides information on numerical control systems and computer numerical control (CNC) systems. It defines numerical control and describes traditional NC, CNC, and DNC systems. It discusses the basic components of NC systems including software, machine control units, and machine tools. It also covers CNC machine construction, driving systems, tooling systems, applications, advantages, and disadvantages of NC and CNC machines. Finally, it discusses topics like part programming fundamentals, coordinate systems, canned cycles, and micromachining.

1. UNIT 4

2. NUMERICAL CONTROL SYSTEM
– Numerical control refers to the automation of machine tools
operated by programmed commands encoded on a storage
medium against to manual control through hand wheels or
mechanically automated through cams alone.
– Controlling a machine tool by means of a prepared programme is
known as Numerical Control or NC

3. Definition of NC System
– A system in which actions are controlled by the direct insertion of
numerical data at some point is known as NC system.

5. TYPES OF NC SYSTEM
– Traditional numerical control (NC)
– Computer numerical control (CNC)
– Distributed numerical control (DNC)

6. Controlled axes in NC systems

7. NC axis conventions

8. Basic components of NC
– Software
– Machine Control Unit (MCU)
– Machine tool

9. Machine Control Unit

10. – Input or reader unit
– Memory
– Processor
– Output channel
– Control panel
– Feed back channel

11. CLASSIFICATION NC MACHINES
BASED ON CONTROL SYSTEM
– Open- loop system in NC machines
– Closed loop system in NC machines

12. Open- loop system in NC machines

13. Closed loop system in NC
machines

14. Classification NC machines based
on numerical control system
– Point to point NC system
– Straight cut NC system
– Contouring NC system

15. Point to point NC system

16. Straight cut NC system

17. Contouring NC system

18. Driving system of NC Machines
– Electromechanical devices
– Digital circuits

19. AC Drives
Principle of operation
The velocity of AC synchro motor is controlled by
manipulating the voltage frequency supplied by the motor. The
frequency manipulation requires the use of an electrical inverter, the
inverter contains DC power supply and the circuit inverts DC voltage
into AC voltage with a continuously controllable frequency.

20. DC MOTORS

21. STEPPING MOTOR
– Principle of operation
The drive unit contains a steering circuit and a power
amplifier. It translates the input pulses into the correct switching
sequence required to step the motor.

22. HYDRAULIC SYSTEMS

23. PNEUMATIC DRIVES

24. TOOLING SYSTEMS IN NC
MACHINES
– Using quick change tool holders
– Automatic tool selection
– Changing tools automatically for sequence of operations

25. APPLICATIONS OF NC
MACHINES
– Metal cutting machine tools
– Press working machine tools
– Welding machines
– Inspection machines
– Assembly machines
– Industrial robots
– Cloth cutting

26. ADVANTAGES OF NC
MACHINES
– It provides greater accuracy
– Less production cost
– Less operator skill is required
– Machine utilization is better
– Tooling cost is less
– Cycle time is reduced thereby increasing the tool life.

27. DISADVANTAGES OF NC
MACHINES
– Machine cost is high
– Highly knowledgeable person in this field
– Flexible is not there

28. CNC SYSTEM
– Computer numerical control is a NC system that utilizes a stored
programme to perform the basic numerical control functions. A
mini or micro computer based controller unit is used.

30. The type of CNC used in these
above- said fields are given below
– CNC lathes
– CNC turning centres
– Gear hobbing machines
– Gear shaping machines
– Tube bending
– Electron beam welding
– Press brakes
– Abrasive water jet machines
– Coordinate measuring machines

31. Types of CNC
– Hybrid CNC
– Straight CNC

32. Major Elements of CNC systems
– Hardware
– Software
– Information

33. CNC Machine Constructional
details

34. Special features of CNC
machines
– CNC drive systems
– Feed drive
– Slide movement element
– Swarf and coolant control
– Working of automatic tool changer
– Work holding system
– CNC controller
– Type of CNC machines

35. Special features of CNC
machines
CNC drive systems
1.Cutting spindle
A spindle drive is a primitive type of transmission. A rod, referred to
as a spindle, is attached to the output of an engine. This rod then
comes in direct contact with a tired. A spindle tooling provides an
objective connection between cutting tool and spindle of the
machine tool.

36. Special features of CNC machines
CNC drive systems
1.Spindle heads
Types
i) Inclinable head
ii) Robot-head
iii) Horizontal spindle head
iv) Vertical spindle head
v) Universal head.

37. CNC drive systems
Feed drive
Feed drive consists of a feed servomotor and electronic controller. Unlike a spindle drive, the feed
drive motors has some special characteristics such as constant torque and positioning. Also, in
contouring operations, several feed drives have to work simultaneously because of the requirement
to follow a prescribed path continuously.

38. Slide movement Element

39. Working of automatic tool changer
– Drum type
– Chain type

40. Swarf and coolant control
In CNC grinding process metal chips are formed in the form
of micro particles. This particles is known as swarf.
During of CNC machining process, the coolant will be mixed
with the swarf and the mixture will be deposited on the
tray.

41. Work holding system
– Collet chuck
– Jaw chuck
– Arbors
– Fixtures

42. MACHINING CENTRES
The following operations are carried out
– Milling
– Drilling
– Reaming
– Boring
– Tapping

43. Classification of machining centres
– Horizontal spindle machining centres
– Vertical spindle machining centre
– Universal machining centre

44. Horizontal spindle machining
centres

45. Vertical spindle machining centre

46. TURNING CENTRES
– Horizontal machines
– Vertical machines

47. CLASSIFICATION OF
HORIZONTAL MACHINES
– Chucking machines
– Shaft machines
– Universal machines

48. Chucking machines

49. CNC ELECTRICAL DISCHARGE
MACHINING
– RAM type EDM CNC machine
– Orbital type EDM CNC machine
– Wire cut EDM CNC machine

50. DESIGN CONSIDERATIONS OF
CNC MACHINES
– Static load
– Dynamic load
– Thermal load
– Guideways
– Measuring system
– Tool monitoring system

52. APPLICATION OF CNC MACHINES
– Metal cutting industry for processes
– In addition to metal cutting machines, CNC has also been applied
to the following
– Press working machine tools
– Welding machines
– Inspection machines
– Assembly machines
– Industrial robots
– Cloth cutting

53. ADVANTAGES OF CNC
MACHINES
– It increases in capacity for storing large part programs
– It increases the memory for part programme processing
– It is easy to edit the part programs on the control console
– CNC is more compatible

54. DISADVANTAGES OF CNC
MACHINES
– Costly setup and skilled operators are required
– Computer programming knowledge is essential
– Maintenance is difficult
– Machines have to be installed in air conditioned places

55. DNC
– DNC can be defined as a manufacturing system in which a number
of CNC machines are controlled by a single computer through
direct connection and in real time.

57. Configuration of a DNC System

58. ADVANTAGES OF DNC
– The computer can be remotely located even a thousand miles
away
– The computer can simultaneously programme for many NC
machines

59. PART PROGRAMMING
FUNDAMENTALS
– The conversion of engineering blueprint to a part
programme can manually be performed or with the
assistance of a high level computer language.
– Part program
– Methods of creating part programming

60. Part program
– The part programme is a set of instructions proposed to get the
machined part starting with the desired blank and NC machine
tool.

62. Methods of creating part
programming
– Manual part programming
– Computer assisted part programming (CAD/CAM)
– Manual data input
– Computer automated part programming

63. CNC MANUAL PART
PROGRAMMING
– To prepare a part programme using a manual method, the
programmer writes the machining instructions on a special format
called part programming manuscript.
– The manual programming jobs can be divided into two categories
– Point to point jobs
– Contouring jobs

64. DATA REQUIRED FOR PART
PROGRAMMING
– Job dimensions/workpiece
– Work holding
– Feed/cutting speed
– Finished dimension with tolerance
– Sequence of operation
– Types of tools
– Mounting of tools

65. COORDINATE SYSTEMS IN
PART PROGRAMMING

66. ZERO POINTS
– Origin is considered as zero point of the coordinate
system. NC machines have either of two methods for
specifying the zero point.
– Fixed zero
– The origin is always located at the southwest corner (lower left
hand corner).
– Floating zero
– The machine operator sets zero point at any positions on the
machine table.

67. REFERENCE POINT
– The part programmer decides the zero point to be located. It is
known as reference point.

68. NC related dimensioning in part
programming
– There are two type of positioning
– Absolute positioning
– The tool locations are always defined in relation to zero point. G90
code is used in a part programme to represent absolute mode
– Incremental positioning
– The next tool location must be defined with reference to the
previous tool location. G91 code is used in a part programme to
represent incremental mode

70. There are two types of unit system
follows
– Inch system
– G70 command is used
– Metric system
– G71 command is used

71. The following steps should be kept in
mind while writing the programme
– Fixation of coordinate system
– Reference of G and M codes
– Dimensions of work and tools
– Locating the fixture and machine table
– Speed and feed according to the work and tool material.

73. PREPARATORY FUNCTIONS (G) IN
PART PROGRAMMING
– Preparatory commands which prepare the machine or
tool for different modes of movement positioning.

76. MISCELLANEOUS FUNCTION IN
PART PROGRAMMING
– The function not relating the dimensional movement of the
machine but it denotes the auxiliary or switching information is
called miscellaneous functions.
– For example coolant on/off, spindle speed

81. Address characters and their
meaning

83. INTERPOLATION IN PART
PROGRAMMING
– It is the process of developing coordinate points in between start
and finish coordinates.
– Interpolation in NC machining is required to calculate the
intermediate points of a curve or straight line when its start and
end coordinates are given. Interpolation may be linear, circular or
cubic/parabolic.

84. INTERPOLATOR
– External interpolator
– Internal interpolator

85. CLASSIFICATION OF
INTERPOLATION
– Linear interpolation
– Circular interpolation
– Parabolic interpolation

86. SUBROUTINES
– The same machining operation which was carried out already is to
be performed at many different operations on the work piece. It
can be executed by means of a means of programme called as
subrouties.

87. CANNED CYCLE
– A canned cycle is a combination of machine moves that performs
anyone particular machining function drilling, turning, milling,
boring, tapping etc.
– G81 to G89 are used for canned cycles
– G80 is used for cancelling the canned cycle

88. MICROMACHINING
– Micromachining refers of the technique for the fabrication of 3D
structure on the micrometer scale. Micromachining refers the
super finishing, a metalworking process for producing very fine
surface finishes.
– The various types of micromachining process are given below
– Bulk micromachining
– Surface micromachining

90. SURFACE MICROMACHINING
– In surface machining process, the structures are created on top of
a substrate. In this case, a silicon substrate (wafer) is selectively
etched to produce structures.
– In this machining the microstructures are built by deposition and
etching of different structural layers on top of the substrate.

91. WAFER MACHINING