Test-riding a 3D-printed mountain bike

Among the displays at the MACH 2014 event, an exhibition for manufacturing technologies held in Birmingham, UK from 7 to 11 April, was a prototype mountain bike designed by Empire Cycles and built by Renishaw. This particular bike was special in that its frame was 3D-printed. At a total cost of £20,000 it’s not cheap, but illustrates the functional abilities of additive manufacturing (AM).

And there has been a lot of interest in the bike, according to Chris Williams, managing director at Empire Cycles. ‘It seems that the world of mountain biking is watching. I am keen to keep people talking. We have spoken to literally hundreds of people and they are very intrigued. Most of the other parts [excluding the frame] were donated by companies, because they wanted to be part of the project, part of something new and innovative. We are very fortunate that everyone wants to be involved.’

The 150mm travel full suspension MX6-R mountain bike came out of an initial project with Renishaw to build just the seat tower using additive manufacturing. The resulting component proved so successful that both parties committed to constructing the whole MX-6 frame using the technique. Williams said that now second and third models of the prototype bike are in the pipeline and should be functional and ready for extensive testing soon.

Both the seat tower and the subsequent bike frame were built from titanium using Renishaw’s AM250 machine. The seat tower was significantly lighter than the standard aluminium version – 200g versus 360g – and proved to be strong, passing EN testing standards by a factor of six. The complete frame weighs 1.4kg compared to the standard aluminium MX6-EVO frame, which weighs 2.1kg.

But the choice of material was not solely down to weight savings, as Williams explained: ‘Renishaw suggested titanium would be a better option for the material because the aluminium powders are not high enough quality at the moment. The grades used are not very high-performance, so the geometries may have to be thicker. Also the heat treatments are potentially problematic.’

However, titanium is expensive and the AM machines aren’t cheap either. Williams said: ‘The major drawback is the cost of the machine that grows the components, and the cost of the materials. Post processing costs are relatively low; the fixturing is often low in cost as well. The big thing to get over is the length of time that the machine needs to build the part, and the amount of material used to do so. These are inherently linked. I don’t think that anybody today knows the answer to get around these issues.’

Williams said that the number of materials that can be processed is quoted to be around 400. He said that, realistically, when designing a functional piece, that this is not the case because the requirements of the material hugely reduce the number of options. He said that for the MX6-R project the team needed a material that ‘needs to be light, so that’s all the steel’s gone; it’s got to take certain stresses, so that’s all the aluminium gone. It’s still in its infancy and they [AM manufacturers] are still developing the materials and their understanding of the machines.’

Williams noted that there’s a lack of standardisation in additive manufacturing – since, often, the powder materials are developed for particular AM machines. He commented: ‘Everybody is trying to develop machines that are commercially viable, but a lot of it is still quite cloak and dagger. A lot of the stuff they are manufacturing is covered by disclosure agreements and the components are sensitive. This is part of why we have been so successful with the marketing of this project, because we have been so open.’ He continued: ‘Doing the bike project has allowed everyone to see what can be done. That’s not to say that this is the best way to do it, we are just having a go.’

The other hurdle that needs to be overcome, in Williams’ opinion, is in the design process, as components should be designed specifically for additive manufacturing. ‘They [parts] are often designed in the traditional way, but grown on an AM machine, and you don’t really want to do that,’ he said. ‘Sections need to be very thin wherever possible because of the heat stresses, you need to try and use small radiuses so that it will self-support, and you need to try and grow the part without overhangs so you don’t need support structures.’

With AM in its infancy, there is a lot of testing and research needed to realise the full potential of the technology.

It is projects like these though that will further AM and show the potential for making metal parts with additive machines.

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