GM's Material Gains

Dec. 21, 2004
Engineering software is key to GM's material optimization process.

As a materials scientist, GM's Alan Taub has no doubt that the auto industry is at least in a new age of materials. "It's actually a revolution," says the executive director of General Motors Corp.'s R&D Science Labs. "We're getting more dramatic substitutions and introductions of new materials than we've had through the entire history of the automobile." Weight reduction is one major goal. His first example: GM's body and chassis design. "Through the 1980s and 1990s, advances in software tools enabled our designers to reduce the structural weight of vehicles by almost 20%. We leveraged computer aided design technology that allowed us to do structural optimization. And we really tightened up the design -- the right thickness and form of the material throughout the vehicle." Starting in the 1990s, material substitution began to accelerate as GM sought materials with higher specific strength and higher specific stiffness. Initially that meant high-strength steels instead of low-carbon steels. Taub estimates that about half of the steel in today's vehicles are new high-strength steel alloys that were not in use as recently as 15 years ago. "That eliminated an additional 10% to 15% of vehicle weight with the potential of being cost neutral." Additional weight reduction is coming from aluminum -- which has the potential of reducing part weight by as much as 55%, adds Taub. That transition began with chassis and power train castings and is continuing with sheet metal components. Magnesium, which is even lighter, is competing with aluminum. Instrument panel supports are one application. The other major play: plastics and composites, including fiber reinforced structural applications. Taub says those materials permit weight savings in the 20% - 25% range. GM also is using polypropylene-based nanocomposites. One application is the body side molding on the 2004 Impala. Design collaboration with resin supplier Basell and Southern Clay Products achieved the required strength at a 7% weight savings. Updated forming technology is also playing a significant role in GM's material strategy. One example is GM's quick plastic forming (QPF) of aluminum. An adaptation of the aerospace industry's hot blow forming, QPF offers the advantage of part consolidation. With QPF one forming operation can now make convoluted panels that once required two separate parts plus an extra joining step in assembly. The process: a heated aluminum sheet is subjected to high-pressure air that makes it conform to the shape of a hot tool. The deck lid of the Chevy 2004 Malibu Maxx is a current production part. The convergence of material science with the latest developments in information technology permeates GM's efforts. For example, QPF is math-based meaning that the dies are created directly from part design data. That convergence is also evident in the ride control systems developed for the Corvette and Cadillac XLR. The drivers control shock absorber characteristics by magnetically adjusting the characteristics of the shock absorber fluid. The operating principle: iron particles in the fluid respond to the strength of the magnetic field.

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