The United States Council for Automotive Research (USCAR) has demonstrated the capability to mould large structural reaction injection moulded (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 fibre preform is placed in a matched metal mould and low viscosity resin is rapidly injected.

The resin quickly impregnates the fibres 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 programme 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 programme 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 save 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 fibre preforms and achieved high material usage rates and lower cost.

The production quality mould was designed with shear edges to allow use of an injection-compression process and production of net-edge parts requiring minimal trimming.

The mould incorporated a vacuum to assist in mould filling and fibre wetting. The use of real-time monitoring equipment helped define and optimise moulding 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 moulding 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 fibre preforms.

Manufacturing advancements were made in SRIM for the production of large structures and cored parts. Technology was also developed in the durability characterisation of polymer composites, adhesive materials, and NDT methods.

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