Düsseldorf, October 15, 2024 – Fabric roofs for convertibles are highly complex assemblies when it comes to safety, look, and functionality. Designing them is therefore always challenging. The example of the new convertible from a German premium automotive manufacturer illustrates the new opportunities that high-tech thermoplastics open up in the design of such parts. Its fully automatic fabric acoustic soft-top is equipped with a roof crossmember at the front that is made from the lightweight Tepex® and Durethan® structural materials from Envalior. They act as substitutes for magnesium. Envalior will present the crossmember at the Fakuma 2024 trade show.
The crossmember holds the actuators and kinematics used to lock and unlock the soft-top with the roof frame of the body structure. Until now, these components were integrated in a magnesium assembly with a plastic cover. However, this cover was visible in the interior and reduced the length of the roof liner. The assembly is now made mostly of high-performance plastic.
“Thanks to the greater freedom of design the plastics from Envalior offer and the flexibility regarding the choice of materials, it was possible to close the component at the bottom and extend the roof liner to the A-pillars. This gives the vehicle interior a more homogeneous, harmonious, and therefore elegant overall appearance. In addition, this design weighs 700 grams less than the previous magnesium versions and allows 50 percent of the necessary components to be saved,” explained Matthias Schütte, Product Manager Structural Lightweight Global at Röchling Automotive, the manufacturer of the soft-top crossmember.
The design of the crossmember was extremely challenging due to the tight installation space, the complex geometry, and the high loads.
“Nevertheless, we managed to design a plastic component in accordance with the design specifications that also meets the high requirements regarding safety, function, and look,” Schütte explained. This success was possible thanks to the close cooperation between Envalior and Röchling Automotive.
“In addition to our design materials, we also contributed various engineering services to the project. We offer these kinds of services to partners to assist them in all stages of development of a plastic component, all the way to the start of series production. This expertise pays off for our customers in the context of challenging, innovation-driven new projects in particular,” said Dr. Klaus Vonberg, Sales & Business Development Manager Tepex® at Envalior.
The soft-top crossmember is located at the edge of the convertible’s soft-top and connects firmly with the roof frame of the windshield when the roof is closed. The structural component is produced using hybrid molding technology. This method combines the forming of a thermoplastic fiber-reinforced composite with injection molding in just one tool. A section of continuous-glass-fiber-reinforced and polyamide 6-based Tepex® dynalite 102-RG600 from Envalior is used as a composite here. It constitutes the front edge of the soft-top crossmember and reinforces the overall component. Durethan® BKV50H2.0 is the injection-molding material used. This polyamide 6 compound is reinforced with 50 percent glass fibers by weight and is also made by Envalior.
The plastic soft-top carrier is trough-shaped and is subsequently sealed with a cap that connects to the fabric soft-top. The delicate and load-path-compatible internal structure of the carrier holds mounts, guides, bearings, openings, and fasteners, for example. Implementing these even approximately using magnesium die-casting would have been an extremely complex undertaking. For example, there would have been a considerable need for rework. In contrast, there is just one process step in the hybrid molding method that produces a rework-free plastic component into which numerous functions are integrated by means of injection molding.
The Envalior engineering services for the soft-top carrier also included detailed mold-flow analyses for mold filling. Filling the cavity in the hybrid molding method is not easy, as the component has a complex internal structure and is very wide. As a result, the molten plastic has correspondingly long flow paths. A gate concept by means of which the large tool can nevertheless be filled evenly was developed. This way, the formation of weld lines, which impair the mechanical performance of the structural component, can be largely prevented.
Mold-flow analyses also helped to minimize warpage of the component and determine the local orientation of the glass fibers in the component. The latter is an important input parameter for precisely calculating various mechanical load cases by means of integrated simulation.
“We studied various crash substitute load cases and analyzed the forces that are applied to the component as a result of the soft-top fabric tension under wind load as well as of seal compression. We adapted and optimized the component design on the basis of the results, taking into account the tolerance requirements when integrating the component in the body,” Vonberg explained.
The carrier illustrates how useful it is to use Tepex® in the lightweight design of structural and body components. This applies to components in the upper area of the vehicle (greenhouse) in particular.
“Our lightweight composite material helps to lower the vehicle’s center of gravity and thereby improve vehicle dynamics,” emphasized Henrik Plaggenborg, Director Global Sales & Business Development Tepex® at Envalior.
For example, Envalior has already succeeded together with partners in developing an A-pillar for the Porsche 911 convertible with a Tepex® composite design. “We expect that it will be possible to implement B-pillars and C-pillars, roof bows, and even entire frames for windshields as well,” Plaggenborg continued.
Aside from components in the greenhouse, the composite design with Tepex® also has a good chance of being used in the lower body, for example for reinforcing door sills, longitudinal members, and crossmembers. The composite material could act as a substitute for metals in all of these applications and thereby help to reduce weight, which increases the range of electric vehicles, for example.
Fakuma will take place at Friedrichshafen Exhibition Center, from October 15 to 19, 2024. You can find Envalior’s stand in Hall B4, booth #4302.
For more information on the products and services provided by Envalior, visit www.envalior.com.
The roof crossmember is made from the lightweight Tepex® and Durethan® structural materials from Envalior. The design of the structural part was extremely challenging due to the tight installation space, the complex geometry, and the high loads. Nevertheless, it was managed to meet the high requirements regarding safety, function, and look.
Photo: Envalior
About Envalior
Envalior is a global leader in Engineering Materials with over 4,000 employees worldwide. It was established in 2023 through the merger of Lanxess Performance Materials and DSM Engineering Materials. With a long track record of customer-driven innovation, Envalior specializes in developing sustainable and high-performance material solutions. Focus markets include Automotive, New Mobility, Electronics & Electrical, and Consumer Goods. For more information, visit www.envalior.com.
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Candace Roulo
