JEC COMPOSITES MAGAZINE - Issue #45 - November/December 2008 - 36

FEATURE “Automotive” be necessary. The available EF systems can be used to incorporate EF tapes of various thickness, width and, of course, length. g…/… smart fortwo tailgate: the first high-volume application of E-LFT technology properties, but provide excellent design freedom and enable the economical production of large components. Unidirectional continuous fibre tapes (EF) have excellent mechanical properties and can be inserted three-dimensionally to conform to load paths and component geometry. LFT components can thus be strategically reinforced with EF inserts. With this combination, the E-LFT process enables the production of complex load-bearing moulded components, widening the application window for such components to include use as substitutes for components previously manufactured from metals. More or less the same materials are used for EF and LFT, usually glass fibres in a polypropylene matrix . However, other fibres and matrices, e.g. PA, PET, PBT or ABS, can also be processed. In the case of EF it can make sense to use carbon fibres in order , to fulfil very high stiffness specifications. The cheap raw materials and the one-step process help to keep production costs low. The low specific density and good mechanical properties of the materials make it possible to produce high-quality, lightweight components. The fact that the reinforcements do not cover the surface, but can be inserted locally and as webbing, results in further weight savings. Fig. 4: E-LFT design freedom. smart fortwo tailgate The E-LFT process was chosen for the new tailgate for several reasons. For one, the smart fortwo 451 tailgate had to have a higher integration potential and better customer utility, while satisfying much higher rigidity and crashworthiness requirements. While the previous smart fortwo 450 model used a different design for each version, a single structural concept was preferred for the new tailgate. Fig. 3: E-LFT process layout. smart fortwo coupe 450 To satisfy quality and cycle time requirements, the E-LFT process is designed for fully-automated production. The main stages of the production system are: LFT-D processing, EF processing, handling (by robots) and the press (Figure 2). LFT is compounded directly or can be provided as rod-shaped material. The EF processing unit was especially developed for this process. The handling system was also specifically developed for quick transport and accurate positioning of the LFT and EF tapes. A frame-type press with synchronized travel such as those used for LFT processing is used. The E-LFT process is designed so that the EF tapes are inserted according to load and to conform to component design. Thus, the tapes can be inserted in almost any configuration. This way, the reinforcements (EF) optimally match the forces arising. One of the main process features is the use of multiple EF tape layers. Since most components have to transmit more than two forces, several EF tape inserts are required. The tapes may even criss-cross (Figure 4). Depending on the requirements, various EF cross-sections may smart fortwo cabrio 450 a. the tailgate consist of a tubular aluminium frame and a PPTV20 inner part, b. no storage space. a. the tailgate consist of an ABSPC inner part with flap, b. in a frontal crash, the roof edges are retained with belts. Fig. 5: Design concepts of the tailgates for the previous smart fortwo 450. In the previous version of the coupe, the tailgate consisted of a tubular aluminium frame and an inner part in PP-TV20. There was no flap, and thus no storage space. In the previous cabrio, jec composites magazine / No45 November-December 2008

JEC COMPOSITES MAGAZINE - Issue #45 - November/December 2008

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #45 - November/December 2008