Fast performance for performance vehicles

Automotive Design & Production, Dec, 2006 by William Kimberley

CRP's Windform laser sintering process family currently comprises Windform GF, Windform PRO and Windform PRO B whose identifying characteristics are the stiffness and the Ultimate Tensile Strength (UTS). The latest addition to the family, though, is Windform XT, a carbon fiber-based material for SLS technology for true rapid manufacturing applications. It is similar to CarbonMide, the carbon fiber filled polyamide material marketed by German company EOS, the two companies getting into something of a squabble earlier in the year over patents rights. CRP's Windform XT material has a low density (1.1g/cm3) and a high tensile strength (77.85MPa) and tensile modulus (7320.8MPa), which means that it has an exceptional ultimate tensile strength per unit density of 70.71 MPacm3/g and a tensile modulus per unit density of 6649.2MPAcm3/g. The surface finish on as-built parts is 6.0microns (Ra), and a finish of 1.8microns (Ra) can be achieved after finishing. For parts up to 150mm the standard tolerance is [ or -]0.3mm, while the tolerance on larger parts is [ or -]0.05mm per 25mm. Its excellent detail definition, stiffness, resistance to vibration and can be used to create thin and intricate parts with high strength.

Its light weight, high UTS characteristics, excellent surface finish, and resistance to wear, compared to standard SLS Duraform and SLS GF Duraform, also lends the technology to the low-volume direct manufacture of parts for race cars and motorcycles without the weight penalty. CRP was already using its Windform GF material to create parts for Formula One cars but things like brake ducts, air intakes, cooling ducts and bodywork flaps are now produced in Windform XT. The material is also being used for components on World Championship motorbikes including the chain pad, head cover, water pump cover, seat, mudguards, windscreens and airbox. It is also the preferred SLS material for wind tunnel models due to its strength and stability under wind load and vibration while it has even found applications on a road car even if it is at the exotic end of the scale and found on the Lamborghini Gallardo.

"The main improvement with Windform XT," says Cevolini, "is the homogeneity of the material. It is now very easy to achieve good surface quality, reliability during the build process and accuracy. It is also quite simple to attain good mechanical properties without any warpage at all." Some of the potential applications for Windform XT are also related to vehicle engines, so laboratory tests have been performed to quantify the material's characteristics at elevated temperatures. After soaking the test pieces in an environmental chamber for at least 90 minutes, the material's tensile strength, yield strength and tensile modulus (E) have been analyzed from data collected at five temperatures ranging from 60[degrees] up to 150[degrees]C. All three material properties were found to decrease moderately with an increase in temperature, with values at 150[degrees]C being in the region of half those at 60[degrees]C. Indeed, the pattern observed is very similar to that for PA6BG-35, a glass-filled polyamide that is typically used to produce injection-molded components for automotive applications.