NOV 2018


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47 Pushing EVs Forward also channel air from crush cans — that double as air intakes — at the front of the car through internal aluminum radiators to cool the batteries. is eliminates conventional radiators up front, minimizing the entire front structure of the car, as well as the aerodynamic drag of heat exchangers. e aluminum- finned radiators also work as controlled crush zones around the batteries, increasing impact protection. e 38 battery modules located within the monocoque provide not only the EV's power but also structure. Each 136-mm-wide battery module contains 10 pouch-type lithium-ion batteries (think thin, as for a laptop) from LG Chem (Seoul, South Korea). Pouches are stacked and protected within a CFRP box. Each of the 38 battery module boxes are made using flat CFRP sheet and the highly automated 223 process. Portions of the sheet for the box faces are cured, leaving flexible uncured hinges in between. ese hinges allow the folding of the partially cured sheet into a box, followed by final cure and bonding to produce a rigid enclosure. Each box is an impact-resistant, load-bearing exoskeleton, aiding in crash safety. e boxes are individu- ally located and secured together to provide significant torsional and bending stiffness through the monocoque. is, in turn, handles some of the load that otherwise would be managed by the CFRP side rails, and thus, allows the design to be further lightweighted. rCF wishbones e FW-EVX uses CFRP wishbones to cut weight 40% vs. conventional aluminum versions, yet cost is comparable to aluminum forgings thanks to the RACETRAK process. As reported in a May 2017 article by Engineering UK magazine, RACETRAK is based on high-pressure resin transfer molding (HP-RTM) and was developed with the National Compos- ites Centre (NCC, Bristol, UK). e FW-EVX wishbone design combines three fiber formats with one resin. Unidirectional material wraps around an anchor point to increase strength with near-zero waste, while recycled carbon fiber (rCF) — up to 80% of the composite part, by weight — in the form of a nonwoven mat, helps reduce cost and increase sustainability. Epoxy and polyurethane resin are already in use for high-volume HP-RTM composite suspension parts (see Learn More). According to Iain Bomphray, Williams Advanced Engineering's chief tech- nology specialist for lightweight structures, the rear wishbone was the thickest part ever made in the NCC's press. e resulting CFRP structural control arm (photo, above) can be molded in 90 seconds, with a 5-min total cycle time, including layup. Flexibility for future development ough it uses CFRP extensively, the FW-EVX platform was designed to also use aluminum in the monocoque and suspen- sion. e materials and forming technologies selected are opti- mized and located to meet overall vehicle performance and efficiency goals. e platform was also designed to be flexible. For example, the battery module currently uses LG pouch cells, but can accommodate multiple battery formats. e off-the-shelf powertrain components, chosen for high performance, may also be readily exchanged for manufacturer-specified alternatives. Meanwhile, Williams is working to further develop and test the FW-EVX platform. "We've applied our extensive knowledge in composites and systems to totally rethink how electric vehicles are designed and built," says Bomphray. "What sets us apart is not just our abilities in design and manufacturing, but getting all of the systems and structures to work together. We've been able to reduce aerodynamic drag and weight, as well as complexity, and invest those savings into greater power, safety and vehicle range." CW senior editor Ginger Gardiner has an engineering/ materials background and more than 20 years of experience in the composites industry. RACETRAK rCFRP wishbones The FW-EVX uses CFRP wishbones made using unidirectional and recycled carbon fiber (rCF) in an HP-RTM process called RACETRAK. Source | Williams Advanced Engineering

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