CompositesWorld

OCT 2018

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NEWS CompositesWorld.com 67 Thermoplastic Composites 7 After dispensing adhesive, robot prepares to bond glass to top of sunroof system. 8 Fully assembled and pretested module ready to install on vehicle. The sunroof's water seal is carried on the glass and is achieved using the PUR adhesive that joins the glass to the rest of the module. 9 The pre-assembled sunshade module with glass roof is positioned by robot onto the vehicle and then bonded to the vehicle roof. Compared to thermoplastic composites, those wet out with thermosets tend to be higher in density, have slower molding cycles and require more post-mold finishing. Further, remelt- able thermoplastics offer an adhesive- and fastener-free assembly option and enormously simplify end-of-life recy- cling. Plus, thermosets introduced concern about possible fogging and volatile-organic compound (VOC) emis- sions, which are tightly regulated for vehicle interiors in the European Union. Owing to OEM requirements for extremely tight dimen- sional control — particularly to avoid warpage, which would impede smooth operation of the sunshade — polyamide, polypropylene (PP) and thermoplastic polyesters were elimi- nated. Because aluminum rails require grease for smooth sunshade operation, and because Webasto engineers weren't sure yet if lubricant would be needed on composite rails, polycarbonate was eliminated due to its poor chemical resis- tance and tendency to stress crack. Acrylonitrile butadiene styrene (ABS) was rejected due to the sunroof 's 110°C thermal requirements. e Webasto team had previously used fiberglass-rein- forced styrene maleic anhydride/ABS (GR-SMA/ABS) for the moving-glass sunroof frame, so it focused attention on this material, which has been used in the automotive industry for decades for instrument panel substrates. GR-SMA/ABS is low-density, stiff and strong, has very low warpage and low deformation over a broad range of temperatures and humidity levels. Because it's amorphous, there's no concern with post- mold crystallization and shrinkage. Additionally, it's melt reprocessable, welds nicely and its maleic anhydride compo- nent ensures high bond strength to a variety of substrates, including the polyurethane structural adhesive used to join the glass roof to the sunroof module. Webasto turned to its GR-SMA/ABS resin supplier Poly- scope Polymers BV (Geleen, e Netherlands) to suggest grades that would work. Polyscope supplied two possibilities — 15%-GR XIRAN SGH30EB and 30%-GR XIRAN SGH60EB — which were then subjected to small-scale lab testing at Webasto. e 30%-GR grade was stiffer, but its higher E modulus was not required to ensure smooth operation of the sunscreen. Tests indicated the 15%-GR grade would meet mechanical property targets, so the team opted to use that material, not only for left- and right-side rails but also for the front cross-beam. e rear cross-beam remained in GR-PP. e next decision was what process to use to produce the rails. Initially, profile extrusion was considered because it can produce both hollow and solid shapes, and functionally it resembles the process used to produce aluminum profiles. It's also a continuous process, fast enough to meet production requirements, yet its tooling costs are relatively low. Unfortu- nately, researchers were concerned that extrusion wouldn't produce smooth enough interior surfaces from fiber-rein- forced resins to enable the sunshade to move smoothly and

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