The big development shown in the Chevy Volt is a high-tech composite that lends itself to mass production. Composites in aircraft are thermosets, usually either polyester or epoxy-based, and usually require long cycle times. GE Plastics is working with several partners on a new thermoplastic approach, but refused to divulge the OEM that will pioneer the use of the new technology. GM said they have no plans to put the composites in their cars in the next two years.
The new high-performance composite technology (HPPC) developed by GE Plastics features a sandwich of glass mat and thermoplastics made with regenerated plastic scrap. The parts are said to be cost competitive with other materials, and significantly lighter. The technology was shown in January on the Chevy Volt concept car at the Detroit Auto Show. The newly announced drive by President George W. Bush to reduce gasoline consumption in the USA by 20 percent within 10 years will give the technology another boost.
One of the biggest hurdles has been the development of a new processing technology that will allow the hoods to be made in less than three minutes. Another potential roadblock was painting, which will initially take place off-line, with the goal of full on-line integration. Production cycle time and paintability issues have long been the bugaboos with composite processing technologies, which first debuted on cars in the 1953 Chevrolet Corvette. Major composite technologies for challenging structural applications, such as hoods, have always been theromoset, until now.
The major advantage of thermoplastics is weight reduction. The various thermoplastic innovations in the Chevy Volt add up to a 60-pound weight reduction, estimate officials at GE Plastics. The Volt uses 100 pounds of thermoplastics, including composites in the hood and doors, as well as unreinforced materials in the rear deck lid, roof and fenders.
“The structure of the composite has three layers,” explains Robert Butterfield, global market director of design innovation in the GE Plastics’ automotive business, in an interview with Design News. “The top and bottom layer has a skin, and in the middle is a core. The purpose of the core is to move the compression and tensile areas away from the neutral axis to give it more strength. So what you have is a composite that you would more typically associate with aircraft or race cars.”
GE Plastics has developed an automated system that will use low-pressure matched metal tooling. GE Plastics is using presses and tools at much lower pressures than are used for current thermoset composite molding in cars. As a result, costs are expected to be lower. Initially, however, Butterfield expects that automotive plastics suppliers will be using current equipment to avoid huge capital outlays to get the process rolling. “At the moment we are using aluminum tools,” comments Butterfield, “and they seem to be working quite well. We expect the tools will have a life similar to injection molds because the pressures are so much lower.”
Researchers working with additive manufacturing have said multimaterial techniques will allow industry “to fabricate materials with combinations of density, strength, and thermal expansion that do not exist [yet].”
The term "multiphysics" is used to describe the simulation of multiple types of physics and their influence on one another -- for example, the investigation of the behavior of a chemical in liquid form will involve both chemistry and fluid dynamics.
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