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.