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MANUFACTURING PROCESS-II UNIT-5 NC MACHINE TOOLS
- 1. UNIT 5 – NumericalControl (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 NCSystem – 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 NCSYSTEM – Traditional numerical control (NC) – Computer numerical control (CNC) – Distributed numerical control (DNC)
- 6. Controlled axes inNC systems
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- 8. Basic components ofNC – Software – Machine Control Unit (MCU) – Machine tool
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- 10. – Input orreader unit – Memory – Processor – Output channel – Control panel – Feed back channel
- 11. CLASSIFICATION NC MACHINES BASEDON CONTROL SYSTEM – Open- loop system in NC machines – Closed loop system in NC machines
- 12. Open- loop systemin NC machines
- 13. Closed loop systemin NC machines
- 14. Classification NC machinesbased on numerical control system – Point to point NC system – Straight cut NC system – Contouring NC system
- 15. Point to pointNC system
- 16. Straight cut NCsystem
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- 18. Driving system ofNC Machines – Electromechanical devices – Digital circuits
- 19. AC Drives – Principleof 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.
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- 21. STEPPING MOTOR – Principleof 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.
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- 24. TOOLING SYSTEMS INNC 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 – Computernumerical 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 ofCNC 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 ofCNC systems – Hardware – Software – Information
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- 34. Special features ofCNC 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
- 35. CNC drive systems –Cutting spindles – Spindle heads
- 37. Working of automatictool changer – Drum type – Chain type
- 38. Work holding system –Collet chuck – Jaw chuck – Arbors – Fixtures
- 39. MACHINING CENTRES The followingoperations are carried out – Milling – Drilling – Reaming – Boring – Tapping
- 40. Classification of machiningcentres – Horizontal spindle machining centres – Vertical spindle machining centre – Universal machining centre
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- 43. TURNING CENTRES – Horizontalmachines – Vertical machines
- 44. CLASSIFICATION OF HORIZONTAL MACHINES –Chucking machines – Shaft machines – Universal machines
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- 46. CNC ELECTRICAL DISCHARGE MACHINING –RAM type EDM CNC machine – Orbital type EDM CNC machine – Wire cut EDM CNC machine
- 47. DESIGN CONSIDERATIONS OF CNCMACHINES – Static load – Dynamic load – Thermal load – Guideways – Measuring system – Tool monitoring system
- 49. APPLICATION OF CNCMACHINES – 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
- 50. 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
- 51. 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
- 52. DNC – DNC canbe 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.
- 54. Configuration of aDNC System
- 55. ADVANTAGES OF DNC –The computer can be remotely located even a thousand miles away – The computer can simultaneously programme for many NC machines
- 56. PART PROGRAMMING FUNDAMENTALS – Theconversion 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
- 57. Part program – Thepart programme is a set of instructions proposed to get the machined part starting with the desired blank and NC machine tool.
- 59. Methods of creatingpart programming – Manual part programming – Computer assisted part programming (CAD/CAM) – Manual data input – Computer automated part programming
- 60. 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
- 61. DATA REQUIRED FORPART PROGRAMMING – Job dimensions/workpiece – Work holding – Feed/cutting speed – Finished dimension with tolerance – Sequence of operation – Types of tools – Mounting of tools
- 62. COORDINATE SYSTEMS IN PARTPROGRAMMING
- 63. ZERO POINTS – Originis 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.
- 64. REFERENCE POINT – Thepart programmer decides the zero point to be located. It is known as reference point.
- 65. NC related dimensioningin 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
- 67. There are twotypes of unit system follows – Inch system – G70 command is used – Metric system – G71 command is used
- 68. The following stepsshould 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.
- 70. PREPARATORY FUNCTIONS (G)IN PART PROGRAMMING – Preparatory commands which prepare the machine or tool for different modes of movement positioning.
- 73. MISCELLANEOUS FUNCTION IN PARTPROGRAMMING – 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
- 78. Address characters andtheir meaning
- 80. 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.
- 81. INTERPOLATOR – External interpolator –Internal interpolator
- 82. CLASSIFICATION OF INTERPOLATION – Linearinterpolation – Circular interpolation – Parabolic interpolation
- 83. SUBROUTINES – The samemachining 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.
- 84. CANNED CYCLE – Acanned 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
- 85. MICROMACHINING – Micromachining refersof 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
- 87. SURFACE MICROMACHINING – Insurface 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.
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