Plastics seek problem-solver role

  • 13-Oct-2008 04:21 EDT
09 Corvette ZR1 hood.jpg
The 2009 Chevrolet Corvette uses carbon fiber on its exterior panels, including the hood and front splitter.

The route to a different material solution begins with an idea. In the plastics composite arena, researchers and engineers at General Motors are flush with ideas.

"In the materials area, sometimes the freshest ideas come from Tier 2 suppliers. We get ideas from the entire supply chain, but at times there is a tendency for a provider of an established solution to want that solution to remain in place. The incumbent never wants to be displaced," said Matt Tsien, Executive Director of Global Technology Engineering for General Motors Corp.

A change in materials might be warranted if a proposed solution proves to have value in the context of cross-platform and global applicability as well as demonstrating other merits. The following examples highlight a few of the plastics-composite projects being evaluated by GM researchers.

With weight reduction being a perennial chase for automotive engineers and designers, finding ways to lightweight conventional materials is a constant. "It's possible to reduce the weight and thickness of sheet molded composite [SMC] materials by replacing amounts of fillers and glass fiber with nanoclays. In one development project, a Corvette Z06 carbon-fiber wheelhouse assembly was replaced with a nanocomposite system for a 0.16-kg mass savings and a 35% cost reduction," Tsien said during a keynote speech at the 2008 Automotive Composites Conference sponsored by the Society of Plastics Engineers.

The 2009 Corvette ZR1 has a carbon-fiber hood, roof, front splitter, front fender, and rocker panels. "But one of the problems with carbon fiber is it's absolutely expensive. If we're able to come up with an industrial grade of carbon fiber that meets automotive requirements and has a significant cost savings, that would really drive more use of carbon fiber," said Tsien. GM is working with suppliers to characterize, test, and validate a new carbon-fiber material and process that would net cost savings.

Direct long-fiber thermoplastic (D-LFT) is being eyed as a replacement for current pre-form technology on rear-end compartment applications. "D-LFT presents an opportunity to add ergonomic features, stowage, and other space and parts consolidation at no additional processing cost. We're targeting a project deliverable that would provide a 20% cost reduction in raw material costs and a 35% reduction in tooling costs," said Tsien.

Liquid crystal polymer (LCP) is a material that "has a lot of potential," Tsien believes. While the electrical and electronics industries presently have LCP applications, automotive uses look promising since LCPs have "thermal expansion coefficients roughly equivalent to metals. A primary advantage of using LCPs is the material's extremely high stiffness, which potentially allows for making thin-wall part applications. In addition, the high temperature resistance makes LCPs potentially good materials for under-the-hood applications," said William Rodgers, Technical Fellow at the GM R&D Center, Materials and Processes Laboratory, in Warren, MI.

GM and Wilmington, MA-headquartered Quantum Leap Packaging, a materials supplier, recently produced an approximately 24- x 24- x 0.125-in (610- x 610- x 3.2-mm) test plaque on a 1350-t (1490-ton) molding press at Husky Injection Molding Systems' facility in Novi, MI. "The test plaque is a 4.1-lb part, which is one of the largest LCP parts ever molded," said Rodgers.

LCPs are not that far from prime-time exposure. "If testing and validation proves successful, it's possible that LCPs could be used in production applications like body panels, support brackets, and underhood parts in a time frame that's probably more than two years away, but likely less than five years," Rodgers predicted.

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