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NEWS 25 CompositesWorld.com CFRP: 4,000 parts per day Sixteen CFRP parts make up the Carbon Core, each manufac- tured using one of four technologies (Fig. 1 and see Table 1 in the expanded online version of this article noted in Learn More, p. 30), with each chosen to meet specific part shape and property requirements, yet minimize weight. Michael Ahlers, BMW head of Process Chain Body-In-White and Exterior, points out the Carbon Core parts on a 7 Series BIW displayed at the entrance to the plant's 11,000m 2 CFRP production/logistics area. Noting the B-pillar (Fig. 2, p. 26), Ahlers explains, "It uses CF prepreg covered with a film of epoxy adhesive. Both are hardened to the formed steel B-pillar in one press step." High-pressure resin transfer molding (HP-RTM) is used in the roof rails, made in the nearby BMW Landshut plant, to meet roof pressure test requirements, while wet compression molding (or wet pressing, see Learn More) enables cost-effective, short-duration cycle times for parts such as the tunnel, sills and selected roof bows (Fig. 3, p. 27). When asked about galvanic corrosion, Ahlers explains that for the rear cross member/upper trunk cover (Fig. 4, p. 27), the only CFRP part in touch with aluminum, adhesive is used to isolate the CFRP from the aluminum. ere are no through-hole fasteners to act as a corrosion bridge. Also, the aluminum is painted (black) to prevent corrosion from environmental factors. "e key is to have the right materials and to have them support each other," says Ahlers. e cross member/trunk cover is molded from sheet molding compound (SMC) reinforced with recycled carbon fiber. e fiber is a lofted material, derived from 7 Series waste as well as waste from cutting dry fabrics for BMW's i3 and i8 moldings. ese leavings are carded and formed into nonwoven mat. "In this process, the knowledge is where to put the resin in and how to Fig. 1 Carbon Core: Multi-material BIW The BMW 7 Series body-in-white (BIW) is the first to mate aluminum, CFRP and high-strength steel, a combination BMW calls the Carbon Core. Source | BMW AG 16 CFRP parts 4 different technologies CFRP Wet Compression Molding CFRP Resin Transfer Molding CFRP-Steel Hybrid CF Sheet Molding Compound press it all to avoid dry areas, which happens if you have too much fiber," says Ahlers. "But, if you have too little fiber, you have too much resin and not enough mechanical properties." e recycled carbon fiber SMC parts are not made by BMW, but instead are delivered from a supplier and use epoxy resin. e type of epoxy used, however, is optimized per process. For example, Hexion's (Columbus, OH, US) quick-curing EP TRAC 0600/EK TRAC 06130 epoxy is used in the 7 Series' HP-RTM roof bows and the wet compression molded tunnel. BMW continues to work closely with its resin suppliers. "We have developed faster resins since the i3 and i8," Ahlers notes, Next iteration of i models' CFRP Dingolfing, Germany is BMW's largest manufacturing site in Europe. It produces more than 350,000 cars per year among 15 different models, including three variations of the new BMW 7 Series (left). At right is the BMW i3 all-electric. Source | BMW AG Next iteration of i models' CFRP variations of the new BMW 7 Series (left). At right is the BMW i3 all-electric. Source | BMW AG