3D-printed bike made from Titanium alloy
Renishaw, the UK's only manufacturer of a metal-based additive manufacturing machine, has worked with a British bicycle design and manufacturing company to create the world's first 3D printed metal bike frame.
Empire Cycles designed a mountain bike to take advantage of Renishaw's additive manufacturing technology, allowing them to create a titanium frame that would be both strong and light – using topological optimization – the new frame is 33 percent lighter than the original.
The frame has been additively manufactured in titanium alloy in sections and bonded together, and it's strong – having been tested to EN 14766.
Renishaw and Empire Cycles epitomized the bicycle design for additive manufacture, eliminating many of the downward facing surfaces that would otherwise have needed wasteful support structures.
Titanium alloys have a high ultimate tensile strength (UTS) of more than 900MPa when processed using additive manufacturing, and near perfect densities of greater than 99.7 percent are achieved; this is better than casting and, as any porosity is both small and spherical, it has little effect on strength.
The project's aim is to produce a fully functioning bicycle, so the seat post bracket was tested using the mountain bike standard EN 14766; it withstood 50,000 cycles of 1,200 N. Testing continued to six times the standard without failure.
Testing of the completed bicycle frame will continue, both in the laboratory using Bureau Veritas UK, and on the mountainside using portable sensors in partnership with Swansea University.
From the Greek word for place, “topo”, topological optimization software is the term given to programs that are used to determine the “logical place” for material – normally using iterative steps and finite element analysis.
Material is removed from areas of low stress until a design epitomized for load bearing is evolved. The resulting model is both light (due to the low volume) and strong. The historical challenge in manufacturing these shapes can now be overcome with additive manufacturing, enabling physical 3D models to be realised.
Titanium alloys are more dense than aluminium alloys, with relative densities of around 4 g/cm3 and 3 g/ cm3 respectively. Therefore, the only way to make a titanium alloy version of a part lighter than its aluminium alloy counterpart is to alter the design to remove any material not contributing to the overall strength of the part.
The original aluminium alloy seat post bracket is 360g and the hollow titanium version is 200g, a weight saving of 44 percent. This is just the first iteration; with further analysis and testing it could be reduced further.
The original bike frame weighs in at 2100g. Redesigned to make use of additive manufacturing, the weight drops to 1400g, a 33 percent weight saving.
There are lighter carbon fibre bikes available, but Chris Williams, managing director at Empire Cycles, says: “The durability of carbon fibre can't compare to a metal bike, they are great for road bikes, but when you start chucking yourself down a mountain you risk damaging the frame.”
The key benefit for Empire Cycles is the performance advantages that this construction method offers. The design has all of the advantages of a pressed steel ‘monocoque' construction used in motorbikes and cars, without the investment in tooling that would be prohibitive for a small manufacturer.
Research into bonding methods resulted in Mouldlife providing the adhesive, and 3M providing test facilities. Renishaw will develop this further in partnership to look at iterative improvements in bonding methods, such as specific surface finishes.
A 3D printed mountain bike made by Rennishaw in the UK is given a tough workout on rough terrain.