Bayer introduces sandwich structure technology for automotive body panels

Bayer MaterialScience has developed a sandwich structure that uses a skin molded of continuous glass fiber mats impregnated with polycarbonate. Core is a polyurethane foam.

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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 is showcasing a sample trunk lid that features this technology

"With its smooth, dense outer skin and foamed core, this part has a lot in common with a bone," explains Ulrich Grosser, team leader for advanced technologies at Bayer MaterialScience. The ingenious design of this ultra-stiff but lightweight part of the body is the result of long, evolutionary development. But the similarities end with how the parts are made: While natural bones grow through cell accumulation, Bayer MaterialScience draws on plastics processing methods for the development of sandwich elements.

"To make the outer layer, continuous glass fiber mats are impregnated with a thermoplastic polymer formulated from polycarbonate," Grosser says. "All the fibers are wetted and fully coated by the plastic matrix. This is the key to the high stiffness of the edge layers in a sandwich structure." Polycarbonate blends such as Makroblend shrink minimally, and the process results in a smooth, high-quality surface. It can subsequently be coated to achieve the desired appearance, for example with coatings based on polyurethane raw materials from Bayer MaterialScience.

In a second step, the top and bottom of the trunk lid are joined and the resulting hollow space is filled with a Baysafe polyurethane foam. It is the low density of the foam that makes the component so lightweight. Since the foam is also very stiff, and adheres to the entire outer surface, the component is said to be resistant to minor damage.

In the event of a collision, the foam absorbs energy, enhancing the safety of passengers and pedestrians. It is also a good thermal insulator, meaning it makes a major contribution to energy management inside a vehicle. This reduces fuel consumption and CO2 emissions. In electric cars, these advantages save battery power and increase a vehicle’s range.

Further, the core allows antennas to be embedded in the foam efficiently and permanently. Unlike metal components, polymers permit undisrupted reception across a wide frequency range. Additional functions, up to and including lighting, can be integrated into the sandwich component.

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. "Nature once again proved to be the best master builder in this case," says Grosser. 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. "A network of roots lends even tall and heavy trees a secure hold in soil that frequently is soft."

For a realistic solution, the Bayer researchers optimized the look 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.