NC AND CNC

MANUFACTURING TECHNOLOGY-II

1. UNIT 5 Numerical Control (NC) machine tools – CNC types, constructional details, special features, machining centre, part programming fundamentals CNC – manual part programming–micromachining – wafer machining.

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.

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

5. Controlled axes in NC systems

6. NC axis conventions

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

8. Machine Control Unit

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

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

11. Open- loop system in NC machines

12. Closed loop system in NC machines

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

14. Point to point NC system

15. Straight cut NC system

16. Contouring NC system

17. Driving system of NC Machines Electromechanical devices Digital circuits

18. 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.

19. DC MOTORS

20. 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.

21. HYDRAULIC SYSTEMS

22. PNEUMATIC DRIVES

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

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

25. 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.

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

27. 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.

28. 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

29. Types of CNC Hybrid CNC Straight CNC

30. Major Elements of CNC systems Hardware Software Information

31. CNC Machine Constructional details

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

33. CNC drive systems Cutting spindles Spindle heads

34. Working of automatic tool changer Drum type Chain type

35. Work holding system Collet chuck Jaw chuck Arbors Fixtures

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

37. Classification of machining centres Horizontal spindle machining centres Vertical spindle machining centre Universal machining centre

38. Horizontal spindle machining centres

39. Vertical spindle machining centre

40. TURNING CENTRES Horizontal machines Vertical machines

41. CLASSIFICATION OF HORIZONTAL MACHINES Chucking machines Shaft machines Universal machines

42. Chucking machines

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

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

45. 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

46. 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

47. 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

48. 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.

49. Configuration of a DNC System

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

51. 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

52. 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.

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

54. 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

55. 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

56. COORDINATE SYSTEMS IN PART PROGRAMMING

57. 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.

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

59. 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

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

61. 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.

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

63. 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

64. Address characters and their meaning

65. 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.

66. INTERPOLATOR External interpolator Internal interpolator

67. CLASSIFICATION OF INTERPOLATION Linear interpolation Circular interpolation Parabolic interpolation

68. 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 .

69. 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

70. 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

71. 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.

72. WAFER MACHINING