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Saab Avitronics has developed a hand-held test apparatus for military operational environments using rapid manufacturing technologies such as the selective laser sintering technology and Windform® materials from CRP Technology S.r.l.
(Published on March-April 2009 – JEC Magazine #47)
Saab Avitronics – a joint venture of Saab (Sweden) and Grintek (South Africa) – started to look into the selective laser sintering (SLS) technology at the beginning of the 90s and even used rapid prototyping (RP) for several projects. Unfortunately, the resins available at the time were rather brittle, semi-translucent, and had little use other than for the production of fitment and display models. Saab Avitronics continued to test new RP materials in an attempt to find the best way to produce high-performance parts that save time and money.
New materials, new applications
The strong growth in the land combat vehicle arena heralded the need for a portable, hand-held test apparatus for laser warning systems, such as the LS31 laser warner test set designed for airborne, fixed and rotary winged platforms, maritime applications, and land combat vehicles. The LS31 enclosure had to meet the following specifications: compact, comfortable to use, waterproof, rugged, -25°C to +85°C working temperature range.
Since the customer’s initial request was only for two prototypes, followed by a further eight production units, traditional injection moulding was not considered as an appropriate technology to meet the delivery price and timescale requirements. Machining the components from bar stock aluminium would also be too expensive. Rapid manufacturing was proposed as a solution after discussing the project and the environmental and performance criteria for the test enclosure, whereas Windform® was suggested as a material offering a viable alternative for the production of high-quality, lowvolume enclosures. For all these reasons, Saab decided to use the SLS technology.
Four prototypes were produced with different materials available on the market. For the fourth prototype of the LS 31 laser warner test set, Saab decided to use CRP’s Windform® XT carbon-filled powder. This material was chosen due to its superior performance compared to previously-used materials.
Windform® XT made it possible to 1) produce a significantly lighter part much more rapidly, 2) make more complex shapes, and 3) save money on the cost of the machined part.
The parts were delivered a couple of days after the order was placed. Even though the new design had a much curvier shape, no faceting or steps were visible either on the exterior or the interior. The parts had a beautiful, black, “spark erode” type finish, as if they were produced in an injection tool. As Paul Du Plessis, design manager at Saab Avitronics, comments: “We were astounded. Prototype 4 was very definitely the quality standard we were hoping for, and certainly at a level that we felt comfortable delivering to customers”.
The engraving had good definition and the parts seemed to be quite strong. An added bonus was the conductivity which was accidentally discovered by Saab Avitronics while trying to figure out why the onboard battery of the LS31 kept running flat. (A solder joint touched the inside of the enclosure). This property allowed a certain level of electromagnetic interference (EMI) suppression. The only changes envisaged were small detail design improvements to ensure better sealing and fit of the switches and LEDs. The font size of the engraved characters was also increased and made deeper.
Rapid manufacturing is a versatile technology that enables the manufacture of lowvolume, high-performance enclosures. Parts manufactured directly on a SLS machine benefit from zero tooling costs, and the first batch can be produced in a matter of days. Deliverable high-performance parts are now a possibility due to the availability of more suitable RM materials such as the Windform XT composite material.