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