BMW said this carbon-fiber swingarm was manufactured in a resin-transfer molding process that can help cut the cost and manufacturing time of structural carbon-fiber components (image: BMW).


BMW’s back at carbon fiber with award-winning motorcycle swingarm

BMW rocked the composites world late last year when it announced it was selling its stake in the heralded Moses Lake, WA carbon-fiber production joint venture called SGL Automotive Carbon Fibers. BMW’s pullout from the JV was widely interpreted as a signal that the project to markedly reduce the cost of producing carbon-fiber components for the BMW i8, i3 and 7-Series wasn’t bearing fruit.

BMW insisted it “will continue to rely on lightweight construction and an intelligent mix of materials, with carbon remaining a significant component,” and noted that carbon-fiber will “play an important role” in its iNEXT battery-electric vehicle.

And a recent award to BMW’s Motorrad motorcycle division indicates the company remains intent on “injecting” cost-cutting new efficiencies into the carbon-fiber production process: in March, BMW won a 2018 JEC Innovation Award for the development and manufacture of a carbon fiber-reinforced plastic (CFRP) swingarm manufactured in a newly-developed resin-transfer molding (RTM) process.

BMW said, “The aim of this cooperative venture, bringing together seven partners from industry and research, was to develop a process that enabled the cost-effective, volume-production use of carbon fiber composite materials in structural components subject to high levels of continuous stress. In the case of this particular part,” the company’s statement added, “it was also possible to establish a cost-efficient manufacturing process suitable for the large-scale production of injection-mold components made of carbon fiber reinforced plastic, with CFP tape reinforcements using thermoplastic material.”

In a release, project manager Elmar Jäger said, "We opted for chassis components under continuous load since the requirements involved are especially demanding. Our production technique uses CFP in the form of high-strength endless fibers, where this is required by the stress pattern, while an injection-mold part with short CFP recycling fibers is used where the stress levels are not as high. In this way, we developed a cost-efficient design that can be scaled according to requirements by inserting endless fibers with varying levels of strength in the same tool. The insights we gained from this motorcycle component are equally valuable from the point of view of car development and can be applied accordingly."

Dr. Joachim Starke, the BMW executive with responsibility for funding lightweight composite-fiber projects, said that in addition to reducing the cost and weight of the swingarm, the process enables precise control of the component’s properties “by using a variety of composite and metal inserts” and that there is scalability to enable a single tool to produce a broad range of parts at cycle times of less than a minute.

“All this impacts significantly on cost efficiency as well as part properties,” Starke said.

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