DEC 2018


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47 Multi-material autocomposites necessary to modify both molding process and tool to produce good parts. ese corrugations, in combination with two charges of D-LFT that formed complex ribs in X-shaped lattice structures, generate a high moment of inertia for the area, increasing part sti•ness in the thin, lightweight design while avoiding buckling in a crash. D-LFT lattices at the part's rear formed a crush zone to absorb energy in rear crashes. Aluminum pro les were integrally molded on axial sides of the load -oor and bonded to D-LFT and laminate via special surface treatments as well as holes that provide interlocking. ese pro les were carefully designed to further increase part sti•- ness, provide good buckling behavior and transfer force into the D-LFT crush zone during a crash. ey also provide attachment points for direct mounting of the rear load -oor to surrounding metallic structures. Additional metallic inserts, also integrally molded into the structure, provided direct mounting for seatbelt locks. Successful implementation Simulation work as well as small- and large-part testing veri ed that the entire hybrid rear load -oor could be used to manage crash loads. Further assessment revealed that this technology should be as safe as conventional metallic structures. One larger project goal — reducing total BIW mass to ˆ‰‰ kg — was theoretically met during simulation and small-part devel- opment. However, as the project evolved, better crash perfor- mance was desired, which required adding mass to composite structures. In addition, cost considerations led to a switch from carbon ber to glass ber reinforcement for the rear load -oor. e resulting rear load -oor weighs Œˆ.Ž kg, while the front load -oor (with inserts but without batteries) weighs "ˆ." kg. For nal test parts, the mass target was missed by just "% for a total BIW mass of ˆ‰– kg to achieve higher safety and lower costs. e SMiLE BIW also would be more costly than conventional metallic systems owing to the intensive use of carbon ber reinforcement in the front load -oor. e rear load -oor project led to F-ICT's development of a D-LFT/compression process called local advanced tailored LFT, which selectively applies D-LFT material to largely UD-tape struc- tures to produce locally complex geometries (like ribs) that cannot be made with tapes. Another F-ICT technology developed before SMiLE but used on the project is a method to rapidly heat and consolidate thermoplastic tapes via radiation-induced vacuum consolidation, a technology now commercially available from Die•enbacher on a machine called Fibercon. Remarkably, the experimental process and highly complex tool produced by Frimo worked from the start and more than "‰‰ parts were produced for subsequent testing and demonstration. Although the team designed the molding process to be done in a single step, Dr.-Ing. Sebastian Baumgärtner, F-ICT team leader for thermo- plastic processing and leader of the rear load -oor project, believes that in a production environment it would be more eŸcient to form this complex part in two steps, with laminate preforming done in a separate tool. "We opted to try the harder one-step process rst and it worked well," Baumgärtner explains. "However, the tool was very complex and process control was not so easy. If the laminate got too hot in spots, it had a very strong interaction with the LFT strands. To ensure good repeatability during production, it would be better to simplify things and choose a two-step process, which would be more robust." Still, given the large size of this composite part and the complex process used to form it, the team was very pleased with the end results. "We demonstrated that we could produce an inno- vative and economic part that was weight and performance opti- mized and featured high functional integration using commercial technology," he adds. e complete load -oor won the ˆ‰"– CCE-JEC Innovation Award in China and the German government recognized the larger SMiLE program as a Lighthouse project, meaning the technology will be important for use in future mobility design. e team is in discus- sion about next steps. Contributing writer Peggy Malnati covers the automotive and infrastructure beats for CW and provides communications services for plastics- and composites-industry clients. Read this article online | Read more about the development of a new D-LFT/compression molding subprocess | FIG. 3 Molding trials for load floor design During the final molding trial for the rear thermoplastic composite load floor, more than 100 test parts were produced (top). Some of those were joined with the front thermoset composite load floor and side rockers to produce demonstrator parts for further evaluation (left). Source | Fraunhofer Institute for Chemical Technology

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