01 June 2001
01 June 2001
The United States Council for Automotive Research (USCAR) has demonstrated the capability to mold large structural reaction injection molded (SRIM) parts through the work of the Automotive Composite Consortium (ACC).
SRIM is a promising process for the manufacture of composite structures that have a high degree of part consolidation, improving cost-effectiveness relative to stamped metal structures. In this process, a glass fiber preform is placed in a matched metal mold and low viscosity resin is rapidly injected. The resin quickly impregnates the fibers and rapidly crosslinks to form the rigid polymer matrix.
The use of structural polymer composites in cars and trucks can significantly reduce vehicle mass and thus decrease fuel consumption. However, the industry has historically been limited in its ability to cost- effectively manufacture large structural parts in high volume. According to Program Manager Doug Denton of DaimlerChrysler, "This technology can be very beneficial in the effort to reduce the weight of vehicles, but the cost has been prohibitive. The goal of this program was to address issues -- like cost -- that have been associated with the production of large SRIM structural composite parts."
The project showed the feasibility of producing parts at a relatively rapid rate that meet performance criteria and saves weight, while costing no more than a steel structure. Use of a fully-automated, robotic process, P4, produced consistent net-shape, net-size chopped glass fiber preforms and achieved high material usage rates and lower cost. The production quality mold was designed with shear edges to allow use of an injection-compression process and production of net-edge parts requiring minimal trimming. The mold incorporated a vacuum to assist in mold filling and fiber wetting. The use of real-time monitoring equipment helped define and optimize molding process parameters.
The structural inner of a pickup truck box was selected as the primary demonstration part. A cost model was developed to assess the cost of the composite box assembly relative to a steel assembly using similar production scenarios. The cost model indicated an SRIM composite pickup box can be cost competitive at annual volumes of up to 50,000 units.
Researchers demonstrated the feasibility of achieving a four-minute production rate for the pickup box. The box meets performance requirements and weighs 25 percent less than a corresponding steel structure. "ACC, with the help of our supplier partners, met the goals of the SRIM project and advanced the state of high-volume, low-cost liquid composite molding for use in the automotive industry," Denton said. Key among the development accomplishments was advancement of P4 as a means to reliably produce net-shape, net-size random chopped fiber preforms. Manufacturing advancements were made in SRIM for the production of large structures and cored parts. Technology was also developed in the durability characterization of polymer composites, adhesive materials, and NDT methods.
ACC functions under the umbrella of USCAR -- a cooperative of DaimlerChrysler, Ford and GM established in 1992. The purpose of USCAR is to assist the domestic auto industry in facilitating pre-competitive research.