CompositesWorld
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NOVEMBER 2016 28 CompositesWorld PLANT TOUR us to use a thinner, more lightweight steel part," says Wolferseder, "saving 2 kg while providing superior crash performance." Dingolfing Body Shop A short drive from the CFRP Shop is the 40,000m 2 Body Shop, where CFRP parts and metal parts from the Press Shop are joined into modules, which then are assembled into the 7 Series BIW. CW's tour here is led by Christoph Roth, head of production for the BMW 7 Series Body-in-White. Scanning the floor from an overhead viewing bay, the high degree of automa- tion is obvious — 460 robotic arms are used in the shop's 7 Series section alone, overseen by 130 technicians per shift. Roth explains that CFRP parts come into this building through an exterior washing area where dust from machining is removed. "All of the parts do this except for the B-pillars because they are not machined and they are also not bonded during BIW produc- tion, only welded," Roth explains. "is washing and then drying is necessary because all of these parts will be bonded, so the surfaces must be very clean." e CFRP parts are fed into the Body Shop on a just-in-time (JIT) basis, directed from the overall produc- tion control system. After drying, the parts are sent to one of the 20 automated production cells that join the CFRP parts to metal. ese cells produce parts for all 7 Series derivatives, including left and right hand drives and the extra-length version. "Figuring out how to join all of these parts and the production cells needed was the challenge," says Roth. "Every joining method already existed somewhere in the automotive industry, but the challenge was how to bring it all together with these new materials and make it all work for our production cycles." e roof frames and lower sill reinforcements are glued and riveted, but the rivets are used only to hold the glued surfaces in contact until the epoxy adhesive cures. "We decide on what fasteners to use depending on where the part is in the car, the material and also the access," he explains. "If you can only access one side, then you use flow-drill- screws, for which we have also developed very innovative new technology." e latter require no pilot hole, feature an undercut beneath the heads and very fast installation, which heats up the surrounding material and, as a result, "welds" the fasteners in to a degree. Roth continues, "We use 150 flow-drill-screws per each 7 Series BIW. If the machine can gain access to top and bottom, then we can use rivets." Roth describes one area where fasteners have been eliminated: "e aluminum casted part that is glued to the CF SMC rear support replaces up to 30 separate parts but has now been inte- grated into a one-piece unit." Walking past multiple rectangular, fenced-in produc- tion cells, each with two or three robotic arms moving parts through various prepa- ration and joining operations, he points out a worker who is performing ultrasonic inspection on a completed subassembly. Fig. 7 Tunnel workcell Robotic arms apply epoxy adhesive to the CFRP tunnel, checking placement, width and continuity via cameras before bonding to metal components. Source | BMW AG Fig. 6 Wet pressing of sills Wet compression molding of sills begins with robotic applica- tion of epoxy resin onto flat NCF stacks. These are transferred to a mold (a, b) and pressed (c). Source | BMW AG A B C