numerical control. machines machines are everywhere utility machineries eg. buses, planes ...
Post on 15-Jan-2016
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Numerical Control
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
Manual machines
Control by levers, cams, etc.
Can you identify common operations?
Dimensions of control
On/Off, Speed Linear motion
Position Direction
Circular motion Angle
Process specific Tool changes Current
Control system
Input – Compare – OutputInput: SensorsCompare: ComputerOutput: Servo motor, speed controller, etc.
How a NC machine know its state?
Open-loop Initialisation State updated on every operation
Close-loop State feed-back from sensors
How a NC machine know its state?
Sensors
Limit switchesElectronic position sensors
Control system
Small, reliable computerData input and storageExecute control codeDrive peripherals and motors
Output
Most common output is servo motorA smart motor that can turn a specific,
small angle accuratelyThe control system send a PULSEOn receiving the PULSE, the motor turn
an angle (an increment)
Output
Drive
Ball-screw connected with the servo motorMost CNC controller can specify up to
0.001mmGood CNC can achieve 0.001mm position
accuracyLow-end CNC can achieve around
0.01mm
Limit of resolution
0.001 X 0.001 mm theoretically
Freeform curves and surfaces are approximated
Real-world limitations
In real-world it is affected by Motor start/stop Backlash Momentum Vibration
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
Tool-path generation
Define machine stepsGenerate proprietary codesConvert proprietary codes to G-CodeTransfer to NC controller
Tool-path generation
Common CNC milling tool-path types
Rough cut UV cut Parallel plane
cut Pencil trace
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
CAD issues
Surface gaps Boundary edges Minimum radii
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/machine/vertex/02.html
5-axis Machining
Adapted from: http://www.mitsuiseiki.co.jp/en/machine/vertex/02.html