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Zinc casting specialist boosts precision with laser scanning

29 September 2013

At PMS Diecasting, products are inspected by non-contact, 3D laser scanning to an accuracy of 2.5 microns, mirroring the precision of touch probing.

This is made possible by the deployment of a laser scanner and LK ceramic bridge co-ordinate measuring machine supplied by Nikon Metrology. The combination has proved to be the answer to the challenge PMS was facing to bring its products to market faster and reduce development costs.

Widely regarded as one of Europe's leading and best equipped manufacturers of zinc castings, Rotherham based PMS has many high profile customers including returnable transit packaging specialist, Loadhog, window and door hardware supplier, Avocet, and wire joining and tensioning product manufacturer, Gripple, for which PMS makes 36 million castings annually. 

The diecaster prides itself on using the most advanced technology and incorporates robotics wherever possible to streamline processes and make them more efficient and cost-effective. Automated part separation, 100 percent quality control and management control systems ensure consistent quality. PMS managing director, Gordon Panter takes up the story:

"To avoid zinc flash forming at the parting line when a mould closes, the maximum allowable tolerance when machining the two die halves is plus or minus ten microns. Our optical profile projector and measuring microscope do not have the necessary resolution to inspect to this level of accuracy, but the Nikon equipment does. We considered both laser and white light scanning systems, but decided on the Nikon Metrology LC15Dx laser scanner, as it was the only solution that could inspect our tooling to the accuracy we wanted.”

Order of magnitude improvement
The equipment is easily capable of inspecting tolerances of ±20 microns required on cast parts as well as features down to half that limit on the tooling that produces them. Freeform surfaces as well as geometry can be captured to the same high level of accuracy, ten times better than previously possible at PMS. As a result, time-to-market for new products has been reduced and development costs are lower. Mr Panter again:

"Our improved measuring capability led us to become increasingly critical of the tools we were buying in from external suppliers and this led to the decision to start making our own tools to gain control over their accuracy. It resulted in the formation in 2012 of our ‘GoTools’ subsidiary, which not only produces die casting tools for PMS, but also enables us to reliably design and manufacture plastic injection moulds, forging dies and press tools for other companies."

One of the drivers for PMS investing in the new metrology equipment was an increasing amount of work being carried out for the automotive sector - Jaguar Land Rover included - that required a higher level of accuracy and repeatability than was needed in the past. The diecaster also intends to target the medical industry, which also demands top precision components. 

High quality tooling is key to successful die casting. The laser scanner is able to monitor the toolmaking process as it progresses to make sure that the moulds, and hence the cast components, will be within tolerance.

Cavities, cores, slides, electrodes, ejector pin plates and other features are inspected individually after they have been machined, along with the jigs and fixtures holding components during manufacture. The approach avoids introducing errors into the tool as it is assembled.

As Mr Panter points out, people usually assume that what comes off a modern CNC machine tool is correct, but often it is not. "With the Nikon equipment, we know definitively if each part is within tolerance, so our tools are always spot-on and right first time, guaranteeing the precision and quality of our products and those of customers using our tooling," he adds.

Combining laser scanning and touch probing
3D scanning is today the default inspection mode at PMS for freeform parts and standard features, while cores and other deep features are measured with a touch probe, which is also used to align components on the granite table prior to inspection.

Either the laser scanner or a probe is mounted in a Renishaw PH10M motorised indexing head for maximum flexibility when programming measuring cycles using Nikon Metrology's multi-sensor CAMIO software platform. It supports laser scanning and touch probe scanning where needed and has highly productive reporting functionality, ideal for ISIR (initial sample inspection report) approval in the automotive industry.

Using Nikon Metrology Focus software, which manages the point clouds acquired during laser scanning, inspection data can be compared against the customer's original CAD model. Colour deviation analysis shows how the 3D scanned model differs from the nominal CAD file.

This provides a detailed insight into form and features, providing many more data points compared to touch probing. The colour map scales can be adjusted to reflect manufacturing tolerances and annotations quantify deviations from nominal at selected areas. 

If two or more products are scanned - for example, to monitor wear - multiple objects can be compared showing where each differs from the other. Dimensions extracted from sections of the scan model can be correlated with those on an original 2D drawing, creating an instant ISIR report.

New ventures
3D laser scanning at Rotherham has spurred another PMS venture – the provision of a reverse engineering service for local firms. Highly accurate CAD files have already been produced for plastic injection moulders that did not have any digital data to work from, only physical parts, allowing faithful reproduction of the components.

Mr Panter was surprised at how many enquiries he received after announcing the service on the PMS website and has decided to open a new reverse engineering division to expand this side of the business.

Die casting manufacture and the new toolmaking and reverse engineering divisions were consolidated earlier this year into new premises opposite the company's existing facility in Rotherham, which will double the available floor area. It will also accommodate the plant and staff of a separate toolmaking company recently purchased by PMS to strengthen its prismatic machining, grinding, spark erosion and general toolmaking capabilities.

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