Introduction

1. Introduction History, Advantages, Disadvantages, Applications, Elements of Machine Control

2. Introduction to the concept of computer numerical control

3. Definition of Numerical Control (NC): • A versatile form of programmable automation in which machine movements and various other functions are controlled by instructions expressed as a series of letters, numbers and symbols initiated via an electronic control system.

4. History • 1725; England, punched cards were used to control the cloth pattern of knitting machine operation • 1863; automatic player piano, used air passing through holes in a perforated paper drum to control keyboard mechanism in a preprogrammed sequence. • 1952; first NC machine built by MIT

5. Direct Numerical Control: NC machines are operated directly from a remote computer

6. Computerized Numerical Control (CNC): late 60's early 70's: • When the control system utilizes a dedicated internal computer positioned on the machine. A dedicated computer is built into the Machine Control Unit (MCU) of one machine tool.

7. The internal computer allows for the following: • Storage of additional programs • Program editing • Running of programs from memory • Machine and control diagnostics • Special routines • Inch/metric-incremental/absolute switchability

8. 6 Elements of CNC system: • 1. Part program • 2. Program input device • 3. Machine control unit (MCU) • reads and interprets coded instructions for machining the particular work piece, then generates electric output signals • 4. Drive system • 5. machine tool • 6. Feedback system (sometimes)

9. Advantages of CNC: • Increases productivity • High accuracy and repeatability • Reduced production costs • Reduced indirect operating costs • Complex machining operations • Greater flexibility

10. Adv. (Continued) • Lower operator shill required • Facilitates flexible automation • Reduced rejection rates • Reduced tooling costs • Improved production planning and control

11. Limitations of CNC: • 1. High initial investment • 2. High maintenance • 3. Not cost effective for low production levels

12. Applications of CNC: • 1. Chip removal • 2. Grinding • 3. Unconventional Machining • 4. Fabrication

13. Specifically: • Metal, wood, plastic, etc. cutting • Flame cutting, waterjet cutting, laser cutting • Sheet metal forming and punching • Electrical discharge machining (EDM) • Welding

14. Fewer employees will be required but those needed will be technicians with knowledge of metal-cutting methods, cutting speeds and feeds, work holding, and tool set-up

15. Cannot eliminate human involvement totally from the machining process. • There is no automatic control system capable of making a decision in the true sense of the word. Its capability is restricted to responding to a manual or computer prepared program

16. Elements of Machine Control

17. 1. Slide movements • Hydraulically actuated pistons • Electric servo motors (common) • Axis of movement are X, Y, & Z (sometimes referred to as U, V, & W) • Z axis is always related to motion parallel to the spindle axis • Length of travel of slide movement is called “Coordinate Dimension” • Slide movement caused by Servo

18. Parameters of control for slide movements • Starting and stopping • Direction • Feed rate (how fast) • Distance

19. Rotary Movements • A about X • B about Y • C about Z

20. 2. Machine spindles • Electric motors • Hydraulic motors

21. Parameters of control for spindles • Stopping and starting • Direction (CW or CCW) • Speed of rotation

22. 3. Tooling • Turrets • Magazines (chain) • Manual intervention

23. 4. Work holding • Automatic (electric, hydraulic, pneumatic actuated vises, chucks, collets, robots, pallets) • Manual intervention

24. 5. Supporting functions • Apply coolant • Blast of air to clear chips • etc.