3D printed steel frame is lighter than titanium
The Materials and Advanced Manufacturing Research Group (MOD3RN) at Nebrija University in Madrid has created a motorcycle frame by 3D printing it from powered steel - the result is lighter than conventional designs made from aluminium or even titanium.
Backed by steel producer AcelorMittal, the project uses readily available materials in the form of powered steel and known 3D printing technology, using lasers to selectively fuse the material together in layers, building up the entire frame in a series of slices. The challenge was to meet the rigidity requirements of a motorcycle frame while using the absolute minimum amount of material.
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The project had to develop computer algorithms that allow the operator to enter details of key hardpoints of the chassis - the engine mount positions, for instance, and the steering head and swingarm pivot location - as well as the required level of rigidity. The computer can then work out a layout of frame struts that meets those requirements and which can be 3D printed with the least material.
It is the latter part of the process that is critical - the frame struts are all hollow, with walls between 0.8 mm and 1 mm thick, and normal 3D printing would require those hollow areas to be filled with support structures. By placing the frame struts at particular angles, and orienting the frame correctly during the print process, the Nebrija algorithms eliminate these supports, significantly reducing weight.
Sergio Corbera, engineering director at the university, said: "The possibility of generating hollow parts was the main unknown in metal 3D printing. We are talking about wall thicknesses of between 0.8 and 1 millimetre in the chassis. This involved addressing several issues within 3D printing: stability of the piece during the printing process as a result of the very low thicknesses, control of porosities and mechanical properties in these thicknesses, and orientation of the geometric shape to avoid internal supports."
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The resulting prototype frame, designed to suit a single-cylinder race bike, weighs just 3.8 kg, compared to around 5 kg for a similar frame made from aluminium using conventional processes. A normal steel trellis frame of the same size would be 6 to 7 kg.
Since the 3D printing process is relatively slow, taking hours to build up the frame, layer after layer, it's not ideally suited to mass production (yet!). However, it could be a game-changer for prototyping during the R&D phases of a new bike's design, allowing new iterations of chassis to be created relatively quickly and with minimal manual engineering input into either the design or construction.
