Rapid prototyping 'shows its metal'

Written by: Tom Shelley | Published:

Tom Shelley reports on advances in rapid prototyping, such as the manufacture of more efficient heat exchangers and hydraulic manifolds.

Additive methods are allowing the manufacture of heat exchangers that are more efficient than conventional devices and can handle multiple fluids, while it also possible to make hydraulic manifolds which more than halve fluid flow losses.

Initial applications are seen in aerospace and motorsport but, as costs of machines reduce and technology continues to improve, such techniques are likely to expand into a wider range of industries. As an example of what can be done, 3T RPD in Newbury has made a novel heat exchanger out of 316L stainless steel using DMLS – Direct Metal Laser Sintering. CEO Ian Halliday explains that, as well as being of a very unusual geometry, which could not be made any other way, it possesses struts or 'Turbulators' inside the tubes to prevent laminar flow and encourage turbulence and so improve heat transfer.

DMLS using metal is not quite as straightforward as SLS (selective laser sintering) using plastic, because metal, particularly stainless steel, has a melting point well over 1000°C and conducts heat. This means, according to Halliday, that normally "you have to support it or it sags". However, the demo heat exchanger was self-supporting, without any pillars or supports that would need to be cut off afterwards. "The trick is", Halliday explains, "to make all surface parts so that they are more than 35° to the horizontal." This was achieved in the design by making use of Within Enhance software and working in partnership with Dr Siavash Mahdavi, managing director of Within Technologies, to generate the structure. The tubes are tear drop shaped and the outside has also been designed to increase the cooling surface area.

The construction has additionally been designed to impart structural strength into whatever product it is intended to form part of and can be made in any shape.

As well as generating the shape and ensuring a minimal angle to the horizontal, the software allows the design to be optimised for structural strength and/or minimal mass. Initial potential applications are in motorsport, particularly F1 and aerospace. Saving 100kg is said to save 4 million tonnes of CO2 emissions, as well as a substantial cost saving over the working life of an aeroplane.

The other project on which 3D RPT has been working is a hydraulic manifold. As Halliday explains, by using additive manufacturing "you can have curved tubes, inside instead of right angled bends, which reduces fluid pressure drop and improves flow by one and a half to two and a half times". He cites here studies undertaken by Red Bull Racing.

DMLS can be applied to titanium and Inconel alloys and aluminium is now also available. In other RPD developments, Glidewell Laboratories, which provides dental laboratory services to North America has announced its latest collaboration with Objet Geometries using Objet's 'Eden' 3D printing systems. Z Corp, on the other hand, has introduced two new 3D printers, the monochrome ZPrinter 150, priced at £10,900 and the multicolour ZPrinter 250, priced at £17,900. Resolution is 300 x 450dpi, minimum feature size is 0.4mm, vertical build speed is 20mm/h and build size is 236 x 185 x 127mm. Finally, the trophies presented at this year's Hungarian F1 grand prix were made by Materialise using SLS polyamide and subsequently lacquered in gold, silver and bronze. The Eni trophies are made as a series of linear elements that represent a fire-breathing, six-legged dog.

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