Materials and technologies advance rapid prototyping

Tom Shelley reports on some the latest steps forward in equipment and processes for rapid prototyping and short run manufacturing

Ink jet 3D printing and curing has taken a step forward with the launch of a new and greatly improved machine, and users are taking 3D laser sintering into new regions with new designs and new materials, hard or impossible to make with conventional technologies.

The InVision si2 3D printer, announced towards the end of last year by 3D Systems, has finally come to market with ten times tougher material at 25% less cost than its Thermojet predecessor. Material is inkjet printed, along with a support wax with a microscopic lattice structure that can be melted away in an oven. The work piece moves beneath the print head and is cured by an ultra violet flash in a separate compartment after the deposition of every third layer. Curing away from printing improves the lives of print heads, which clean themselves at the start of each build and according the company, "Should last for years."

The base material costs $100 for a 0.45 kg cartridge with $50 for a similar amount of support material. A small figurine costs about £3 to prototype, and can be produced within a few hours. Senior Director, Product Management, Mervyn Rudgley explained that the factor limiting speed of production is heat build up - the time for each layer to cure and solidify. Refrigeration has apparently been considered but is so far rejected on account of cost.

Selective Laser Sintering, originally developed by DTM, is increasingly being used to make short run production parts, particularly complex air ducts for advanced fighter aircraft and short run luxury cars, where tooling costs for conventional injection moulding would be prohibitively expensive. In addition, SLS can be used to make parts with internal fins and dividers that could not be made in one piece by any other method. Rudgley told Eureka that in addition to the stainless steel powder infiltrated with bronze that the company has developed to make injection mould tools, an unnamed aerospace customer has expressed a strong interest in infiltrating steel powder with epoxy resin. Their intention is, apparently, to produce parts with higher stiffnesses per unit weight than can easily be made out of conventional materials. Others are infiltrating aluminium alloys powders with a second aluminium alloy of lower melting point and a next generation of powders from 3D Systems is to include mixtures based on tungsten carbide.

Researches into producing components whose mechanical properties vary by using powders of changing composition and into producing rapidly prototyped micro girders by various methods continue. An InVision si2 machine currently costs £55,000.

Durham Pipeline Technology
Mervyn Rudgley


* Invision si2 works with 0.04mm layers. Build envelope is 300 x 185 x 203mm. Build speed is 6.5mm/hour

* Prototype material is an acrylate gel at room temperature, supported by a wax, melted out subsequently

* New materials are becoming available for the separate SLS process with a view to produce short run production parts with properties and geometry difficult or impossible to achieve using conventional technologies

Tom Shelley

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