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Vacuum casting process speeds prototyping

A Paragon Rapid Technologies product story
Edited by the Engineeringtalk editorial team Sep 13, 2005

Paragon Rapid Technologies has produced a range of prototype radiation detection devices using its advanced two-shot vacuum casting process.

Paragon Rapid Technologies has produced a range of prototype radiation detection devices using its advanced two-shot vacuum casting process.

Paragon was selected as the preferred prototype supplier to Cambridge Design Partnership in the development of the first isotopic personal dosimeter (IPD) for the first response market.

Existing radiation monitors used by the fire service were sometimes impractical and this new pocket sised IPD is designed to be wearable and capable of detecting a broader range of radiation more accurately.

The product measures the intensity of incident radiation through a cadmium-telluride pixilated sensor.

Paragon produced a range of prototype models of the main casing including SL models for evaluation and then two-shot vacuum castings for marketing and field trials.

Two-shot vacuum casting simulates multimaterial injection moulding and, according to Paragon's Phil Adamson, has always been perceived as a technical challenge by many prototyping companies.

Alignment between the substrate and elastomer parts is often difficult and this, coupled with other problems such as coloured substrates showing through the rubber parts, often leads to impractical scrap rates of up to 30 or 40%.

Adamson and his partner, Peter Humphrey, therefore decided to invest substantial R and D time in developing, refining and testing their own multi-step process, particularly the production and setting up of the silicone tools, so they could guarantee high quality prototypes for their clients.

Paragon's two-shot vacuum casting involves a four step process, commencing with the production of two SL models - the first of just the rigid element of the component and the second of the complete component.

These models are then finished to an exceptionally high standard.

Silicone tools are then produced of both models using special tooling techniques developed by Paragon to ensure faultless filling and venting.

Rigid parts are then vacuum cast in the normal way, in the case of the IPD using ABS and polycarbonate simulants.

Then, again using positioning techniques developed by Paragon, the substrate parts are located into the combined tool for overmoulding with a PU rubber.

In addition to the IPD, Paragon has produced other flawless two-shot vacuum cast parts to simulate multimaterial injection moulding, including a variety of electronic enclosures, razors, mobile phones and soft grip handles for power tools.

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