AUG 2018


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47 CF SMC Front Chassis Subframe body-mount connections and two steering-mount connections where stainless steel sleeves are overmolded into the composite part. "For attachment, each body-mount bushing gets press-fit into the sleeve for an interference fit," Krull explains. "Stress is driven into the molded part through the circumference of the sleeve. We looked at forces when the bushing is inserted and input those into the computer design models. We also looked for cracks in the composite material during the physical testing but saw none." Wagner points out that the bolts used are big. "ese are M12 and larger, and must have tight positional, diameter and angular tolerances." is necessitated post-machining once the subframe was molded and assembled. Testing and teamwork Wagner says the prototype subframes will be tested through 2018. "We hope to finish in early 2019 and publish papers on what we've learned," he adds. Ford will perform a suite of corrosion tests at component and vehicle level to explore various corrosion mitiga- tion strategies. Component and vehicle level durability tests will also be conducted, including stone impingement, testing of bolt- load retention and high-temperature cycles. Component tests will include high-cycle fatigue, joint overload, vibration and safety tests. "We are doing our own testing of prototype subframes," says Krull. "is is a very large, complex part to be made from SMC, enabled by the co-molding development. We are looking at how to change the design, the SMC flow during molding and fiber alignment to understand where else we might be able to use these materials." "We wanted to understand the largest cost drivers with this kind of CFRP-intensive part," says Wagner. "Secondary machining is one of the most significant costs. We need to think more creatively to eliminate machining after part molding." He also notes that one of the biggest challenges was developing the absolute material properties of the as-molded part for the design. "We spent a lot of time on material characterization to feed the design analyses," he explains. "is was time-consuming and expensive. It was a real challenge to get from flat plaques to properties that were representative of real parts because of the material flow during the molding process." Cordoba says the biggest achievement is the teamwork, "not only with Ford as our customer, but as a global team. Wagner agrees: "is is a great example of how we can push our suppliers and ourselves to use advanced, lightweight materials." Overmolding and co-molding Stainless steel sleeves are overmolded into the SMC subframe (top) for four body- mount and two steering-mount connections. Co-molded patches of noncrimp fabric SMC (bottom) were also key, resisting high loads at high-load areas, such as where the top and bottom parts are riveted and adhesively bonded together. CW senior editor Ginger Gardiner has an engineering/ materials background and more than 20 years of experience in the composites industry.

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