At Rotherham-based PMS Diecasting, products are inspected by non-contact 3-D laser scanning to an accuracy of 2.5µm, mirroring — the company says — the precision of touch probing. This inspection has been made possible by the use of a laser scanner on a ceramic-bridge co-ordinate measuring machine. The combination has proved to be the answer to the challenge PMS was facing with regard to bringing its products to market faster and reducing development costs.

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

The die-caster 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% quality control and management control systems ensure consistent quality.

Gordon Panter, managing director of the employee-owned company, says: “To avoid zinc flash forming at the parting line when a mould closes, the maximum allowable tolerance when machining the two die halves is ±10µm. Our optical profile projector and measuring microscope do not have the necessary resolution to inspect to this level of accuracy, but our CMM with laser scanner does.”

The equipment — an LC15Dx laser scanner and LK CMM supplied by Nikon Metrology (www.nikonmetrology.com) — is easily capable of inspecting the tolerance of ±20µm required on cast parts, as well as features down to half that limit on the tooling that produces them. Moreover, both geometry and free-form surfaces can be captured to the same high level of accuracy, which is 10-times better than previously possible at PMS. As a result, the time-to-market for new products has been reduced, and development costs are lower.

Tool production

Mr Panter says: “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. This resulted in the formation in 2012 of our GoTools subsidiary, which not only produces die-casting tools for PMS but also enables us to 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 the increasing amount of work being carried out for the automotive sector (including Jaguar Land Rover), which required a higher level of accuracy and repeatability (the die-caster is intending to target the medical industry, which also demands the supply of top-precision components).

High-quality tooling is key to successful die-casting. The laser scanner can monitor the tool-making 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 that hold components during manufacture. This approach avoids introducing errors into the tool as it is assembled.

Mr Panter says: “People usually assume that what comes off a modern CNC machine tool is correct, but often it is not. However, 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.”

Combined operations

For free-form parts and standard features, 3-D scanning is today the default inspection mode at PMS; 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. The laser scanner and the probe are both used in conjunction with a Renishaw PH10M motorised indexing head for maximum flexibility when programming measuring cycles using Nikon Metrology’s multi-sensor CAMIO software platform. This supports laser scanning and touch-probe scanning where needed and has a particularly productive reporting functionality; it is ideal for ISIR (initial sample inspection report) approval in the automotive industry.

Moreover, by using Nikon Metrology Focus software, which manages the point clouds acquired during laser scanning, inspection data can be compared with the customer’s original CAD model. Colour deviation analysis shows how the 3-D scanned model differs from the nominal CAD file, providing a detailed insight into form and features and offering many more data points than touch probing. Moreover, the colour map scales can be adjusted to reflect manufacturing tolerances, and annotations quantify deviations from nominal at selected areas; and if two or more products are scanned, for example to monitor wear, multiple objects can be compared showing where each differs from the others. Dimensions extracted from sections of the scan model can also be correlated with those on an original 2-D drawing, creating an instant ISIR report.

3-D laser scanning has given rise to another new venture for PMS: 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 (just physical part), allowing faithful reproduction of the components.

Mr Panter was surprised how many enquiries he received after announcing the service on the PMS Web site; he has decided to open a new reverse-engineering division to expand this side of the business. Die-casting manufacture, along with the new tool-making and reverse-engineering divisions, will be consolidated in August into new premises opposite the company’s existing facility in Rotherham. This will not only double the available floor area to 2,600m2 but also accommodate the plant and staff of a separate tool-making company recently purchased by PMS to strengthen its prismatic machining, grinding, spark erosion and general tool-making capabilities.