PU foam-cored glass/PC sandwich structure for auto body panels?

At the K 2103 plastics trade fair in Düsseldorf, Germany, in October, Bayer MaterialScience introduced a new polyurethane-based sandwich structure for use in automotive body panels.

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Bayer MaterialScience (Leverkusen, Germany) reported on Oct. 10 that it has developed a new sandwich structure for use in the manufacture of automotive body panels. At the K 2013 plastics trade fair (Oct. 16-23, Düsseldorf, Germany), Bayer MaterialScience showcased a sample trunk lid that features this technology.

“To make the outer layer, continuous glass fiber mats are impregnated with a thermoplastic polymer formulated from polycarbonate,” explains Ulrich Grosser, Bayer’s team leader for advanced technologies (photo at right). “All the fibers are wetted and fully coated by the plastic matrix. This is the key to the high stiffness of the skins in a sandwich structure.” Polycarbonate (PC) blends, such as Bayer’s Makroblend, are said to shrink minimally, and the process reportedly results in a smooth, high-quality, paintable surface. Finish coatings based on polyurethane (PU) raw materials are available from Bayer.

In a second step, the top and bottom of the trunk lid are joined, and the resulting hollow space is filled with the company’s Baysafe-brand PU foam. The foam’s low density minimizes weight and reduces fuel consumption and CO2 emissions or, in an electric car, it saves battery power and increases the vehicle’s range.

The foam’s stiffness and good adhesion to the outer skin of the part is said to enhance the part’s resistance to minor damage. In the event of a collision, the foam reportedly absorbs energy, contributing to the safety of passengers and pedestrians and enhances thermal insulation, improving energy management inside a vehicle.

Further, antennae can be embedded in the foam, efficiently and permanently. Unlike metal components, polymers permit undisrupted reception across a wide frequency range. Additional functions (e.g., electrical fixtures for lighting) could be integrated into the sandwich component, says Bayer.

To promote the realistic use of the concept part in a vehicle, Bayer also developed an intelligent solution for mounting it to the rear of the vehicle. “The task was to devise a robust and lasting connection between the hinge and the lightweight structure of the trunk lid. To find a solution, we studied how trees are anchored to the forest floor,” Grosser explains. Bayer researchers optimized the shape of the hinge mount using computer-aided engineering (CAE). The resulting plastic structure looks remarkably like the roots of a tree in the ground. Tests confirm that the hinge mount can be attached easily and holds very firmly in the lightweight foam core.