Rapid prototyping and rapid manufacturing technologies have revolutionised product development over the past 10 years, yet further advances continue to be announced by suppliers of both equipment and materials.
Rapid prototyping and rapid manufacturing technologies have revolutionised product development over the past 10 yearsyet further advances continue to be announced by suppliers of both equipment and materials.
In particularthere is a drive to create new materials for use in selective laser sintering (SLS) and stereo lithography (SLA) that will enable truly functional components to be built.
In the early days of rapid prototyping (RP) and rapid manufacturing (RM)it was accepted that relatively accurate models could be produced for visual appraisal.
Both of these approaches to creating functional prototypes or production components require intermediate stages in the processwhich adds cost and time. Hence there has been demand from users of RP and RM technologies for equipment and materials capable of creating parts with enhanced mechanical propertieshigher accuracy and a better surface finish.
Considerfor examplewind tunnel testing. If a wind tunnel test is to give meaningful resultsthe model needs to be an extremely accurate representation of the as-designed component or assembly. For instanceif rivet head forms are inaccuratethe model might not promote the correct transition from laminar to turbulent flowwhich could mean the data gathered is all but worthless. Furthermorewind tunnel models of aerodynamic components may well be subjected to significant loadsso the material must have good mechanical properties if the model is not to deflect and give misleading results.
One company that has responded to the demand is CRP Technologiesof ModenaItaly. CRP Technologies has developed a family of
high-performance materials for use in SLS machines (see panel)the latest of which is WindformXT. This has already been widely used for wind tunnel models and production parts for race cars and motorbikesas well as specialist road vehicles. Now that the powdered material has been shown to have good recyclabilitythe true cost of components is lower than might be expectedwhich is leading to Windform XT being used for less exotic applications where a combination of accuracy and excellent material properties is required.
Windform XT is based on a carbon-filled polyamide and produces black parts with a smooth finish and a sparkling appearance. It 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 70.71MPacm3/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 ±0.3mmwhile the tolerance on larger parts is ±0.05mm per 25mm.
When used for wind tunnel modelsWindform XT offers excellent detail definitionstiffnessresistance to vibration and can be used to create thin parts with high strength. In additionthe black colour assists visibility in wind tunnel testing.
Prior to the launch of Windform XTCRP Technologies was already using its Windform GF material to create parts for Formula 1 race cars. Many of these are now produced in Windform XTsuch as brake ductsair intakescooling ducts and bodywork flaps. Windform XT is also being used for components on World Championship motorbikes (Fig.1). These include the chain padhead coverwaterpump coverseatmudguardswindscreens and airbox. Several bodywork components on the Lamborghini Gallardo road car are also manufactured from Windform XT.
Some of the potential applications for Windform XT are related to vehicle enginesso 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 minutesthe material’s tensile strengthyield strength and tensile modulus (E) have been analysed. Data has been collected at five temperatures: 6090110120 and 150°C.
All three material properties were found to decrease moderately with an increase in temperaturewith values at 150°C being in the region of half those at 60°C. Indeedthe pattern observed is very similar to that for PA6BG-35a glass-filled polyamide that is typically used to produce injection-moulded components for automotive applications.
For applications where temperature is not an issueWindformXT’s advantages lie in its strengthstiffness and the accuracy with which parts can be created. To illustrate these pointsthe manufacturer recently built a scale model of an old design of bicycle (Fig.2). This features epicyclic gears within the front wheelwhich calls for high-precision components and good strength (Fig.3). Components are held together using conventional mechanical fasteners such as circlips and screws inserted in holes tapped in the Windform materialand low-friction bushings are used to ensure smooth operation of the gears and rear wheels .
Although the bicycle is not a typical application for WindformXTit illustrates some of the material’s capabilities. Howeverwhen you also consider that the same material is being used to create production parts for Formula1 race cars and exotic road carsthe huge potential for Windform XT can be appreciated.
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