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Products and solutions, 2000-03-20, 01:00 AM

Automotive segment: Low-Density SMC Competes With Aluminum For Light Weight Body Panels

Strong emphasis on cost and weight reduction has led auto manufacturers to evaluate alternate materials for exterior body panels replacing sheet steel. SMC (Sheet Molding Composite) has been selected for many current car and truck programs. Industry production of SMC has doubled over the past ten years and automotive use of composite materials is projected to continue growing at a rate of over 6.5% per year in the USA. Reduced tooling investment versus sheet metal generally makes SMC cost competitive at production volumes below 150,000 units per year.

SMC body panels typically offer a mass reduction of 30 to 35% versus sheet steel, while providing enhanced styling flexibility, dent resistance and corrosion protection. For weight sensitive vehicles, however, aluminum frequently is studied because of the 50% mass reduction versus sheet steel. Low-Density SMC has a density 30% lower than conventional SMC, with similar physical properties, and thus can provide body panels with the same mass as aluminum.

Density reduction in SMC is achieved by replacing limestone filler with hollow glass microspheres. These low-density composites are used today for inner panel reinforcements on vehicles such as the Corvette. Class "A" surface panels require a surface sealer to cover the porosity resulting from the hollow bubbles; this technology is being developed and should be in production within two years. Long term development may see further density reduction through the replacement of glass fibers by carbon fibers.

Low-Density SMC is a slight cost penalty versus conventional SMC. Compared to aluminum body panels, low-density SMC is very cost competitive because the tooling investment generally is reduced by 50%, or more. The cost-effective production volume versus aluminum may be as high as 230,000 units per year Like conventional SMC, low-density SMC has sufficient heat resistance and dimensional stability to be compatible with automotive paint systems, including electro-coat.

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