Numeric control

numerical control

1. 1 Introduction to Numerical Control Kana Ram Meena (TME15B012) Monil Kantwala (TME15B014)

2. 2 15th century - machining metal. 18th century - industrialization, production-type machine tools. 20th century - tool metal – HSS Automated production equipment - Screw machines Transfer lines Assembly lines Programmable automation - NC PLC Robots Historical Development

3. What is Numerical control? 3 Numerical Control is a system in which actions are controlled by the direct insertion of numerical data at some point. In other words Programmable automation in which the mechanical actions of a ‘ machine tool ’ are controlled by a program.

4. 4 Components of NC Machines MCU Machine Tool CLU DPU MCU – Machine Controlled unit It consists of some electronic hardware that reads the NC programme , interprets it and conversely translates it for mechanical actions of the machine tool . Machine Tool Machine tool is the main components of a numerical control system , which executes the operations . CLU – Control loops unit DPU – Data Processing unit Units which control the input data and execute the required operations .

5. 5 Preparatory functions : Which unit, which interpolator , absolute or incremental programming, which circular interpolation plane, cutter compensation, etc . Coordinates : T hree translational, and three rotational axes . Machining parameters : F eed , and speed . Tool control : Tool diameter, next tool number, tool change . Cycle functions : Drill cycle, ream cycle, bore cycle, mill cycle , clearance plane . Coolant control : Coolant on/off, flood, mist . Miscellaneous control : Spindle on/off, tape rewind, spindle rotation direction, pallet change, clamps control, etc . Interpolators : Linear , circular interpolation Basic Requirement of NC Control

6. 6 Convectional Numerical Control (NC) Direct Numerical Control (DNC) Computer Numerical Control (CNC) Types of Numerical Control

7. 7 Data is sent to the machine tool by means of punch cards or tapes . The reader at the machine performs no calculations or interpolations. Conventional Numerical Control (NC)

8. 8 Direct numerical control (DNC) – control of multiple machine tools by a single (mainframe) computer through . direct connection and in real time 1960s technology Two way communication Distributed numerical control (DNC) – network consisting of central computer connected to machine tool MCUs, which are CNC Present technology Two way communication DNC

9. 9 DNC

10. 10 Computer numerical control (CNC) is the automation of machine tools by means of computers executing pre-programmed sequences of machine control commands. In modern CNC systems, the design of a mechanical part and its manufacturing program is highly automated. The part's mechanical dimensions are defined using computer-aided design (CAD) software and then translated into manufacturing directives by computer-aided manufacturing (CAM) software. The resulting directives are transformed into the specific commands necessary for a particular machine to produce the component, and then are loaded into the CNC machine. Computer Numerical Control (CNC)

11. 11 Advantages : Reduces scrap rate of material Reduces tooling costs Reduces layout time Increases machine and tool life Reduces storage problems Less setup time Reduces actual machining time Allows rapid design changes in part Less jigs and fixture sare needed Advantages and Disadvantages Disadvantages : High investment cost High maintenance effort Need for skilled programmers High utilization required

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13. 13 • Coordinate systems : for flat and prismatic parts, for rotational parts • Motion control : point to point ( PTP), continuous (contouring) path • Control loops : open loop and closed loop • Power drives : hydraulic, electric, pneumatic • Positioning systems : absolute positioning and incremental positioning • Hardware and software : Hardware NC software computer numerical control (CNC ) CLASSIFICATION OF NUMERICAL CONTROL

14. 14   For flat and prismatic (block-like) parts:- -Milling and drilling operations - Rotational axes about each linear axis Coordinate Systems:

15. 15 -Turning operations -Conventional Cartesian coordinate system, but only  x  and z axes -y-axis not needed in turning For rotational parts:- Radial location of the tool Longitudinal axis ( parallel to the rotation axis )

16. 16 Motion Control Systems :- 1-Point-to-Point Systems:- To move the machine table or spindle to a specified position so that machining operations may be performed at that point . Accuracy of the destination is important but not the path . e.g (drilling)

17. 17 2 -Continuous Path Systems :- To control not only the destinations, but also the paths through which the tool reaches these destinations . Use linear and circular interpolators. e.g.(milling and turning) y

18. 18 NC Interpolation methods for continuous path Control : Linear interpolation Straight line between two points in space 2. Circular interpolation Circular arc defined by starting point, end point, center or radius, and direction 3. Helical interpolation Circular plus linear motion 4 . Parabolic and cubic interpolation Free form curves using higher order equations

19. 19 Control Loops:- 1-Open loop:- No position feedback. 2-Closed-loop control :- To measure displacement of table motion. the advantage of a closed-loop system is its positioning accuracy .

20. 20 • Electric motor -widely used -small size, ease of control, low cost • Hydraulic drive -much larger power/size ratio • Pneumatic drive -rarely used in NC positioning system -can be used to drive the auxiliary devices Power Drives:-

21. 21 Positioning systems:- Positions are defined Relative to the origin of the coordinate System (axis system) [x=40, y=50] Absolute:- Incremental:- Positions are defined relative to the previous location of the tool (or next position relative to the present) [X=20, y=30 ]

22. 22 Part Programmer's Job Two main tasks of the programmer: 1.Define the part geometry 2.Specify the tool path

23. 23 Underlying assumption: no matter how complex the part geometry, it is composed of basic geometric elements and mathematically defined surfaces Geometry elements are sometimes defined only for use in specifying tool path Examples of part geometry definitions: P4 = POINT/35,90,0 L1 = LINE/P1,P2 C1 = CIRCLE/CENTER,P8,RADIUS,30 Part Programmer's Job… 1.Define the part geometry

24. 24 Tool path consists of a sequence of points or connected line and arc segments, using previously defined geometry elements Point-to-Point command: GOTO/P0 Continuous path command GOLFT/L2,TO,C1 2.Specify the tool path Part Programmer's Job…

25. 25 Other Functions in Part Programming Specifying cutting speeds and feed rates Designating cutter size (for tool offset calculations) Specifying tolerances in circular interpolation Naming the program Identifying the machine tool

26. 26 • Accuracy =control resolution and hardware accuracy. • Control resolution: the minimum length distinguishable by the control unit (BLU). • Hardware inaccuracies are caused by physical machine errors ( Component tolerances, Machine operation, Thermal error). Note:- • BLU (basic length unit ) NC ACCURACY

27. 27 Example- A machine has 1 BLU = 0.001".To move the table 5" on X axis at a speed (feed rate) of 6 ipm . Calculate pulse rate and pulse count. • pulse rate = speed/BLU = 6 /0.001 = 6,000 pulse/min • pulse count = distance/BLU = 5/0.001 = 5,000 pulses

28. Thank You 28