The battle for lightweighting in automotive is not so much a battle of materials as it is a battle of interesting new technologies. One example comes out of Germany, where lower
production builds and fancier price tags allow engineers to innovate more freely than in other regions.
Chemicals and plastics producer Evonik is promoting a sandwich design using a closed-cell foam that is said to allow a weight savings of up to 60%. In this type of structure, a high-strength core is sandwiched beween sheets of fiber-reinforced thermosets or thermoplastics.
Evonik says its ROHACELL foam combines high strength, low weight and very high heat resistance. The foam core is thermally formed into the geometry required for the component such as a body panel, and is then processed with, for example, high-performance resins at temperatures well above 266F and high pressure.
Molding cycle times are decent: about two minutes. Finished parts are produced in less than four minutes. The foam core is heated along with the thermoplastic face sheets and formed, and in the same operation the two are bonded together, cooled, and removed from the die.
Evonik developed an electric-powered sports car that weighs less than 1,000 kg (2,205 pounds), based in part on its use of ROHACELL fortified with carbon fibers. Weight reduction versus steel is 60-70%. The “Elise-E” was shown at a German Car Symposium last month.
“The purpose of exhibiting the vehicle is to show the automotive industry what can be achieved with our expertise in chemicals,” says Klaus Hedrich, Head of the Evonik Automotive Industry Team. ROHACELL is based on polymethacrylimide (PMI).
Roehm GmbH & Co., a predecessor company to Evonik, was awarded a U.S. patent in 2007 for a method of producing material, especially polymethacrylimide, that is foamed from polymer plates using the casting process.