Numerical Control

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Numerical Control
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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

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Manual machines

• Control by levers, cams, etc.
• Can you identify common operations?

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Dimensions of control

• On/Off, Speed
• Linear motion
• Position
• Direction
• Circular motion
• Angle
• Process specific
• Tool changes
• Current

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Control system

• Input Compare Output
• Input Sensors
• Compare Computer
• Output Servo motor, speed controller, etc.

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How a NC machine know its state?

• Open-loop
• Initialisation
• State updated on every operation
• Close-loop
• State feed-back from sensors

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How a NC machine know its state?
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Sensors

• Limit switches
• Electronic position sensors

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Control system

• Small, reliable computer
• Data input and storage
• Execute control code
• Drive peripherals and motors

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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)

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Output
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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

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Limit of resolution

• 0.001 X 0.001 mm theoretically
• Freeform curves and surfaces are approximated

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Real-world limitations

• In real-world it is affected by
• Motor start/stop
• Backlash
• Momentum
• Vibration

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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

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Tool-path generation

• Define machine steps
• Generate proprietary codes
• Convert proprietary codes to G-Code
• Transfer to NC controller

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Tool-path generation
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Common CNC milling tool-path types

• Rough cut
• UV cut
• Parallel plane cut
• Pencil trace

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Machining issues

• CAM operator has to know
• Tool radius
• Flute length
• Tool length
• Machines zero position
• Workpieces zero position
• Machines working envelope
• Clamp and fixture position

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CAD issues

• Surface gaps
• Boundary edges
• Minimum radii

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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

Adapted from http//www.mitsuiseiki.co.jp/en/mach
ine/vertex/02.html
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5-axis Machining
Adapted from http//www.mitsuiseiki.co.jp/en/mach
ine/vertex/02.html