OCT 2018


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NEWS 65 thermal isolation from the sun and sound isolation from the wind and rain that rigid sunshades do. e conventional manufacturing process for aluminum rails begins with a constant cross-section aluminum profile and requires a labor-intensive, multi-step mill-and-finish process to achieve the rail's complex shape: • cutting to length, • forming small folds via stamping and punching, • shaping curves, • machining/milling complex shapes that cannot be preformed via stamping tools (requires one toolset/ operation and one quality-control check after each step), • anodizing rail in black or natural color, • and assembling electrical cable clips, spiral cable clips, centering/positioning pins and nuts. Every passenger vehicle make and model uses a slightly different shape and length rail, so sunroof manufacturers must produce and stock significant inventory during the production run of a given sunroof module. And when a new model is added, all-new tooling is required unless the vehicle shares common parts with the module for an existing model's sunroof system. Aluminum guide rails are not only labor intensive in produc- tion at the sunroof manufacturer, but also during installation at the vehicle assembly plant. Conventionally, rails are manually fastened via screws to the BIW. en the sunroof module is passed through the windshield bay and bottom-loaded into the opening in the roof where the operator secures it to the recently installed rails. Lastly, the glass roof itself is bonded, via structural adhesive, to the top of the car, sealing the sunroof module and the cabin interior. Although aluminum rails represent known, established technology, they have disadvantages. For one, aluminum is a costly raw material and is more challenging than steel to bend into complex shapes. For another, to protect the environment, disposal of the anodizing chemicals used to prevent corrosion is a significant additional cost. As detailed above, the manufacturing process is long and complicated and its tooling costs are high. Also, efforts to increase functionality require the use of additional hardware applied via additional assembly steps. New rail concept Based on other successful conversions of sunroof frames from aluminum to composites on much smaller-format moving-glass sunroof systems, a team at Webasto decided to conduct a study to see if the much-larger side rails on roller-blind sunroof systems also could be converted to composite. (Front and rear cross-beams had already been converted to composite — typically glass-rein- forced polypropylene (GR-PP) — on such systems.) e goal was to add functionality, reduce manufacturing steps, part count, cost and part weight, yet still meet OEM performance requirements. e team began by studying guide-rail functionality and oper- ating conditions and identified the most critical feature of rails Thermoplastic Composites More space, same protection from sun and sound When retracted, the roller-blind sunshades take up little space under headliners and cannot be seen by vehicle occupants (bottom) yet they still provide the same thermal isolation from the sun and sound isolation from the wind and rain as rigid sunshades. When paired with large transparent, fixed-glass sunroof systems like those offered on the Renault Scenic and Grand Scenic (top), they provide a large daylight opening that spans nearly the length and width of each vehicle's roofline. Source | Renault SAS & Patrick Curtet/Prodigious (top); Renault SAS & Anthony Bernier/Prodigious (bottom) as their ability to facilitate smooth movement of the motor- ized sunshade with the same force front-to-back and left-to- right along the track's path. To achieve that, rails require precise geometry and a constant cross-section along their entire length, which can be greater than a meter. Additionally, the rails have to be sufficiently structural to provide a secure connection to other sunroof/module components, including front and rear sunroof cross-beams and the roof structure itself, the motor mechanism, roof glass and the headliner. To meet OEM requirements, the motorized sunshade has to operate at low sliding-noise levels to reduce noise/vibration/harshness (NVH) in the cabin interior. A scan of commonly used automotive composites quickly elim- inated those with thermoset matrices and favored thermoplastics.

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