The United States Council for Automotive Research LLC (USCAR, Southfield, Mich.), the precompetitive automotive technology organization of Chrysler Group LLC, Ford Motor Co. and General Motors Co., was recently awarded a U.S. patent for an automotive load-bearing composite floor pan developed by the U.S. Automotive Materials Partnership LLC (USAMP) Automotive Composites Consortium (ACC).
The patent applies to a multi-layered fiberglass composite automotive floor pan that defines part of the passenger compartment. The floor pan is configured to absorb or transfer dynamic external loads, or crash forces, which preliminary ACC testing has demonstrated, while maintaining the material integrity of the floor pan.
"The ACC composite underbody project has been a very successful collaboration among a remarkable array of suppliers and researchers from academia and the auto industry," says Libby Berger, project chair and staff researcher in General Motors' Chemical Sciences and Materials Systems Lab. "This patent is among the many great milestones of this project." In addition to the three USCAR-based automakers represented by ACC, others involved in the project include the U.S. Department of Energy, which provided partial funding for the project through a cooperative agreement with USAMP; Multimatic Inc., Century Tool & Gage Inc., Continental Structural Plastics, Wolfden Products Inc., IBIS Associates, Camanoe Associates and researchers from the University of Massachusetts-Lowell.
With automakers continually working to reduce vehicle weight and increase fuel efficiency, Berger said expanding the automotive use of sheet molding compounds (SMCs) for large, lightweight structural components has tremendous potential. The part consists of multiple layers of woven glass SMC material made with a vinyl ester resin. The fabric material is Rovcloth 1854 supplied by Fiber Glass Industries Inc. (Amsterdam, N.Y.). Ribs in the part are formed by additional pieces of structural chopped fiber SMC in localized areas, says Berger, with selective use of low-density chopped glass SMC as a core material in certain areas. The part is compression molded, and a 2.5-minute cycle time is the goal. The floor pan replaces 17 steel pieces and fastening hardware, and comprises the entire floorpan from the engine firewall to the trunk.
ACC researchers are investigating a "weld bonding" method to attach the composite part to the steel vehicle frame, combining spot welding and adhesive bonding. Adds Berger, "If structural composite panels can move into production, one molded fabric SMC floor panel could replace multiple steel parts and shed up to 25 pounds from the weight of a typical passenger car," she says.
Fiberglass fabric SMC, while more structurally robust, has unique and more complex forming requirements. How multiple layers are joined and preformed, and how deformation affects material properties are among the areas continuing to be researched by ACC.