1. Numerical Control

2. Machines Machines are everywhere
Utility machineries eg. Buses, Planes
Manufacturing machineries eg. Injection moulder
Tool-making machineries eg. Lathes, Drills
Tool-making machines are most relevant to Design Engineers

3. Manual machines Control by levers, cams, etc.
Can you identify common operations?

4. Dimensions of control On/Off, Speed Linear motion Circular motion
Position
Direction
Circular motion
Angle
Process specific
Tool changes
Current

5. Control system Input – Compare – Output Input: Sensors
Compare: Computer
Output: Servo motor, speed controller, etc.

6. How a NC machine know its state?
Open-loop
Initialisation
State updated on every operation
Close-loop
State feed-back from sensors

7. How a NC machine know its state?

8. Sensors
Limit switches
Electronic position sensors

9. Control system Small, reliable computer Data input and storage
Execute control code
Drive peripherals and motors

10. Output Most common output is servo motor
A smart motor that can turn a specific, small angle accurately
The control system send a PULSE
On receiving the PULSE, the motor turn an angle (an increment)

11. Output

12. Drive Ball-screw connected with the servo motor
Most CNC controller can specify up to 0.001mm
Good CNC can achieve 0.001mm position accuracy
Low-end CNC can achieve around 0.01mm

13. Limit of resolution 0.001 X 0.001 mm theoretically
Freeform curves and surfaces are approximated

14. Real-world limitations
In real-world it is affected by
Motor start/stop
Backlash
Momentum
Vibration

15. Tool paths The most common control code for NC machines is G-Code
Specialised NC tool-path generators (sometime categorised as CAM applications)
WorkNC
HyperCAM
MasterCAM
Tool-path generation modules
Pro/E NC-POST
CATIA
Unigraphics

16. Tool-path generation Define machine steps Generate proprietary codes
Convert proprietary codes to G-Code
Transfer to NC controller

17. Tool-path generation

18. Common CNC milling tool-path types
Rough cut
UV cut
Parallel plane cut
Pencil trace

19. Machining issues CAM operator has to know Tool radius Flute length
Tool length
Machine’s zero position
Workpiece’s zero position
Machine’s working envelope
Clamp and fixture position

20. CAD issues
Surface gaps
Boundary edges
Minimum radii

21. 5-axis Machining
Capable of approaching a tool from an optimum direction.
The metal molds can be machined by cutting, which have been able to be machined only by a spark erosion machine.
Capable of machining the workpieces by one-time chucking, where conventional machines require setup change.
Reduce metal mold manufacturing time (lead time).
Labor-saving, unmanned operation.
Capable of reducing machining time and improving the quality of machined surfaces.
More roughing allowance can be taken by using a flat end mill in place of a conventional bowl end mill
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22. 5-axis Machining
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