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Product category: Probes, sensors, tool detection, calibration for machine tools
News Release from: Renishaw | Subject: MP700 machine tool probes
Edited by the Manufacturingtalk Editorial Team on 11 July 2001

Probes spark productivity in machining
electrodes

Western Industrial Tooling, an ISO-certified toolmaker has turned electrode machining into a production operation, for competitive moulds with "plug-and-play" 1.3+ Cpk capability

Western Industrial Tooling (WIT), Redmond, Washington, an ISO-certified toolmaker has turned electrode machining into a production operation, for competitive moulds with "plug-and-play" 1.3+ Cpk capability It's ironic that one of the most productive manufacturing processes - plastics injection moulding - has often started out with one of the most laborious, low-production processes; mouldmaking

In addition to all the computer technology that has come on line to shorten mould build time, WIT is using high-accuracy Renishaw MP700 machine tool probes to "spark productivity" in machining its EDM electrodes.

Refusing to pigeonhole probes solely as set-up tools, WIT has developed advanced probing methods both for set-up and post-process electrode inspection, allowing unattended electrode machining at production quantities.

Employing solid state technology to collect accurate data regardless of axis approach, WIT uses the MP700 to probe all its CNC-machined graphite electrodes including very small, very detailed electrodes using ultra-thin styli down to 0.3mm in diameter.

WIT churns out electrodes to keep pace with its CNC EDMs, while maintaining accuracies of +0.000 to -0.013mm.

It is this initial step in the mouldmaking process that demands the tightest tolerances.

WIT builds complex moulds that produce plug-and-play process capabilities of 1.3 Cpk or greater, translating to a defect rate of <1 per million.

They also allow for complete tooling interchangeability from cavity to cavity, mould to mould and are guaranteed for one million cycles, even for telephone connection plugs, printer ink cartridges, and computer mice - some of the most dimensionally critical injection mouldings.

Electrode machining Each new mould begins with a customer-supplied 3-D database for a new part.

WIT programmers use Surfcam to write both the machining program and the probing routine from that database, ensuring that potential mistakes in the machining program are not repeated in the probing routine.

The machining program is downloaded from a central computer to the machine control of one of four vertical milling centres.

WIT machines electrodes, primarily on Mori Seiki and Matsuura machining centres, and doesn't see a need to use dedicated graphite mills.

Each vertical centre is equipped with way scrapers and vacuum systems to handle graphite dust.

WIT has never had to replace a spindle due to dust contamination.

It ensures customer confidence in its machines through annual laser calibration and complete documentation which meets its ISO 9001 commitment.

MP700 for machine set-up Before production begins on a new batch of electrodes, WIT uses the MP700 for machine set-up.

With electrode blanks fixtured, an operator launches a WIT-written macro that directs the MP700 into a ring gauge mounted in the middle of the table.

If the probe determines that the ring gauge has moved from its previous location, all machine coordinate positions are reset in relation to the gauge's new position.

After all milling work has been completed and graphite dust cleaned from the electrode, the MP700 is again loaded for post-process inspection.

The probe inspects the electrode and the data is compared with tolerances defined by the customer (WIT works with 25% of the customer's tolerance).

Any necessary compensating cuts are made at this time, and since the electrode remains mounted on the machine, no refixturing errors are introduced.

With inspection completed and the electrode removed, the MP700 again inspects the ring gauge and makes compensation for any position changes before the next electrode is machined.

After machining and probing, the electrodes are delivered to the EDM department where mould burn-in begins only after a quick check of control dimensions.

After burning, first article and final checks of succeeding moulds are made on the CMM.

MP700 for sensitive on-machine electrode inspection On-machine inspection of an EDM electrode demands that probes are extremely sensitive so as not to break off a delicate part feature or deflect the graphite which would generate erroneous data.

However, the probe must also be rugged enough to withstand jolting machine movements without registering false triggers.

Trigger force on conventional touch-trigger probes is too great and typically non-uniform in different approach directions resulting in unacceptable variations.

The MP700 uses a solid state triggering system employing strain gauge sensors.

When used with a 50mm-long stylus, a low trigger force of only 2gf in X and Y axes and 15gf in the Z axis, allows the use of thin styli to 1.0mm.

However, WIT altered the Renishaw software to permit use of smaller, more delicate 0.3mm CMM styli, necessary because of the ultra-small details on many of its electrodes. Request a free brochure from Renishaw ...

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