CompositesWorld
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JUNE 2015 64 CompositesWorld FOCUS ON DESIGN (including repetitive open/close, ball impact and hot/cold and humidity resistance) was likewise evaluated. Te capstone was a long-term driving test on Germany's famed Nürburgring track (Nürburg, Germany). Te driver reported the test car handled better with the lighter decklid, which lowered the vehicle's center of gravity. In production, prepreg is frst layed up, debulked and cut out. Next, the prepreg is preformed by heating for 1 minute until it reaches 60-70 ° C and immediately shaping it in an air-cylinder press under light pressure (0.3 MPa) using a two-sided tool made from polyurethane modeling board. Preforms are then cooled to room temperature for a total preforming time of <5 minutes. An optional step, when aesthetics are critical, involves covering the preform with a silicone rubber sheet and pulling a vacuum to smooth out wrinkles prior to demolding. If they won't be molded right away, they are stored in containers to keep their shape. Normally, a few preforms accu- mulate, press-side, before being molded. Te molding cycle in a hydraulic compression press is 8 minutes at 140 ° C, using 8 MPa forming pressure. Because both panels are molded to net shape, post-mold trimming is limited almost entirely to removal of a thin parting line fash. Tanks to high molding pressures, parts reportedly exit the mold with a very smooth surface and none of the pinholing seen in autoclave-cured parts. Only light sanding is done to ensure mold release residue is removed prior to painting. Demolded, defashed parts are bonded together with an epoxy structural adhesive. Interestingly, the decklid features a fxed CFRP spoiler/wing. On lower-performance GT-R models, the part is blow-molded in acrylonitrile butadiene styrene (ABS) and painted to match the body, but the premium model with the CFRP decklid features an existing autoclave-cured, clearcoated CFRP spoiler with visible weave. Although only the decklid was produced by the PCM process for the 2014 GT-R changeover, it's possible the wing will be re-engineered for PCM on future models. Challenge buys prepreg from Mitsubishi, cuts patterns, lays up laminates, preforms and molds inners, outers and the autoclaved spoilers, and then bonds the decklid panels. Te unpainted assem- blies are then shipped to Chiyoda, which paints the exteriors, clearcoats the inners and spoilers, bolts on the spoilers, and then ships the completed deck/spoiler assemblies to Nissan's vehicle- assembly facility. Many benefts Despite the curbs on design freedom, the team exceeded its 30% mass-reduction goal, reducing weight by 40%. Mass-decom- pounding efects followed, thanks to assembly lightweighting: Te lighter decklid opened and closed much faster with the struts used on the existing aluminum decklid, so Nissan switched to lighter struts and mounting hardware, reducing mass further. For the car owner, the CFRP decklid opens and closes with less efort, emis- sions are reduced, and fuel efciency, aesthetics and handling (via the lower center of gravity) improve. Te PCM process reportedly can produce 84,000 parts per year per tool, using the 3-minute-cure prepreg, and 50,000 per year per tool, using the 5-minute-cure prepreg. Tat and the fact that PCM components can be molded on conventional — read, readily available — compression presses means CFRP is now accessible to more molders and practical for higher volume platforms. Read this article online | short.compositesworld.com/PCMdebut Read more about out-of-autoclave autocomposites processing options: "Faster cycle, better surface: Out of the autoclave" | short.gardnerweb.com/V4Ty5Iv4 "Sub-8-minute cycle times on carbon/ epoxy prepreg" | short.compositesworld.com/RapidClav3 "Class A CFRP body panels: Six-minute cure" | short.compositesworld.com/WTJigQb9 Contributing writer Peggy Malnati covers the automotive and infrastructure beats for CW and provides communications services for plastics- and composites-industry clients. peggy@compositesworld.com Challengingly thin … The decklid's outer panel, based on the aluminum lid's geometry, was limited to a very thin 1.1 mm — just fve plies of unidirectional carbon fber reinforcement were used in a 0°/90°/0°/90°/0° layup. Source | Nissan Motor Co. Ltd. … and even thinner At 0.7-mm thickness, the aluminum inner panel's geometric limits posed an even greater challenge. Here, a mere two plies of 3K plain-weave carbon fabric, plus local reinforcement, were enough to meet requirements. Source | Nissan Motor Co. Ltd.