CompositesWorld
Issue link: https://cw.epubxp.com/i/517026
JUNE 2015 62 CompositesWorld FOCUS ON DESIGN Prepreg compression molding makes its commercial debut Ultra-thin, preformed laminate designs enable CFRP decklid manufacture at lower-than-expected mass and at cycle times approaching mass-production speed. » One of the biggest hurdles for automakers is developing faster production processes to mold laminate-based carbon fber-rein- forced polymer (CFRP) parts, particularly those with thermoset matrices, which need extra time to crosslink. Conventional auto- clave-cured prepreg produces parts with exceptional mechanical performance, but is capital- and labor-intensive, generates signif- cant consumables waste, requires a great deal of energy and has production cycles typically measured in hours. Fortunately, in the past decade, out-of-autoclave (OOA) processes have been developed that ofer autoclave-like perfor- mance and quality at less cost and several orders of magnitude faster cycle times (see "Learn More," p. 64). One of these is prepreg compression molding (PCM), which makes use of specially formu- lated CFRP prepregs that are preformed, transferred to a conven- tional hot compression molding press, and become Class A parts. Developed by Mitsubishi Rayon Co. Ltd. (MRC, Tokyo, Japan), PCM made its commercial debut on 2014 model year decklid inner and outer panels for the Nissan GT-R supercar, produced by Nissan Motor Co. Ltd. (Yokohama, Japan). But the composite decklid's successful debut was the result, in part, of resourceful design work under a somewhat restrictive set of goals and imperatives. Developmental-turned-commercial part Researchers at MRC started developing the PCM process and its special prepreg around 2007. During development, the viscosity of the prepreg's epoxy resin was increased to prevent resin running out of the tool during high-pressure molding. Further, rapid-cure hard- eners were used to achieve either a 3- or 5-minute cure — the latter ofering longer shelf life at ambient temperatures. Te 5-minute- cure prepreg grade used in this project, called Pyrofl TR361 E250S, was developed by MRC at its Toyohashi Research Center. As work progressed beyond simple test plaques, researchers looked for a prototype automotive part with more complex surfaces to validate the material/process and to demonstrate to OEMs that the system made sense for high-volume part production. MRC had a longstanding relationship with Nissan, and the automaker, for its part, had its own aggressive programs for improving vehicle fuel efciency. Because it recognized that CFRP held promise for mass reduction if cost and cycle-time could be managed, Nissan agreed to share with MRC the geometry and CAD fles for the design of a decklid (trunk lid) on its fagship GT-R supercar. Te understanding was that if MRC's development work showed promising results, then Nissan's engineering team would consider using a PCM'd CFRP part on an upcoming vehicle. MRC's design team worked with the GT-R decklid data between 2009 and 2011. At that point, both organizations believed the material/process had evolved to commercial-part readiness. Te design for a 2014 GT-R model's aluminum decklid was selected, and work on a CFRP version began in 2012. Program goals & challenges As the commercial program began, Nissan and MRC were joined in a team efort by system supplier Chiyoda Manufacturing Corp. (Ota, Japan), material processor Challenge Co. Ltd. (Sayama, Japan) and tooling supplier Yasuda Moldtec Inc. (Kinokawa, Japan). Goals were to produce a part with equal or better mechanical performance but at least 30% less mass than the benchmark aluminum assembly. Because this is a performance car often used on the racetrack, energy management/crash performance was important. Although the failure mode of CFRP parts difers from that of aluminum, the decklid must manage energy well enough to survive a high-speed rear collision, without shattering into small projectiles/debris. Molding speed also was important. Although the frst commer- cial decklid was for the highest performance and, therefore, lowest- volume GT-R model, Nissan was interested in expanding it to higher volume models, and that required a fast process. Further, no one expected CFRP parts to be less costly than aluminum, but they had to remain afordable. Finally, aesthetics mattered. Te decklid's inner and outer panels had to meet automotive Class A require- ments. Te outer shell would be painted to match body color; the By Peggy Malnati / Contributing Writer PCM test case The Nissan GT-R supercar's decklid was a good test platform for the new out- of-autoclave, prepreg compression molding (PCM) technology. The high-end vehicle's two models made it possible to start small and grow into fairly high-volume production. Source (decklid, top) | SPE Automotive Dv. / (car) Nissan Motor Co. Ltd.