Pinpoint accuracy

UK company adapts its own pin tooling process to create injection moulded components without the need for machining.

A UK rapid tooling technology company has developed a production process that can create injection moulded components, such as customised car parts, without machining by using arrays of precision placed pins.

Surface Generation is using a variant of its Subtractive Pin Tooling process that has drastically reduced time and cost for manufacturing components such as military body armour.

The system works by raising arrays of precision pins to create the front face of the tool, and with little or no machining it can produce final specification injection moulded components. ‘It’s a hybridised additive and subtractive technology,’ explained Surface Generation chief executive Ben Halford. ‘A CAD file is processed to provide data to move the pins into the desired shape, and this can either be used directly as an infinitely reconfigurable mould or we skim the top of the pin array by milling to create an exact surface.’

After use, the pin bed can be reformatted for the next job. And if a shape needs modification or the surface is damaged, the affected region can selectively be re-formed in the bed in minutes. ‘It’s fundamentally the same technology platform we’ve been using for three years, but we’ve increased the pin precision and tolerance and the material specification,’ said Halford.

Pins are being made in arrays ranging in sizes from 0.2m x 0.2m to 2m x 1m with a tolerance of up to ± 2.5 microns. The gaps between them are below 15 microns, which means with injection moulding processes no polymer flashes into the joins. ‘The vent on a traditional injection moulding tool would be 20 microns, so we’re below the level where polymer will flash,’ said Halford.

The technology to do this is only possible now because of better CNC equipment and increased economic availability of high-speed grinding, which Surface Generation uses to make its tools. Over the last three years, Halford said his company has demonstrated that its technology can achieve material savings of 60 per cent and a 90 per cent reduction in tooling time for a variety of manufacturers. Individual pins heads can be replaced cheaply and easily and they can be made quickly, which significantly reduces the time for manufacturing the final product.

The only area where the new technology is not yet applicable is stamping of heavy gauge steel. Halford said the company has made significant improvements on the technology. ‘Three years ago, we operated at six bar (90 psi) and 100º C while now we are over 2,000 bar and 350º.’

The major technology step this year was adding injection moulding capabilities, which he claimed no other pin tooling company can boast. ‘We’ve taken a fundamentally different approach to building a reconfigurable mould,’ said Halford.

While the pins on other pin tool technologies platforms beds have been arranged in a 0/90º array, those on Surface’s Generation’s beds are arranged on a ± 45º basis. This is crucial as it simplifies how the pin beds are reconfigured. With other approaches, the middle pin can only move if it has a relatively large gap around it.

Halford explained that these methods can’t cast a liquid on to their pin beds without a membrane in front. He added: ‘We can because we have such small gaps between the pins — that’s why we can injection mould in there.’

The small gaps give the added benefit of allowing the tool to vent excess air which means smaller, more efficient moulding machines can be used. Within the next six months, said Halford, the company will add conformal heating and cooling to the process to reduce cycle times by up to 25 per cent. It is now working with leading European and North American OEMs to optimise the technology prior to full commercialisation next year.