Green SMC Boasts Low Mass

Every auto maker and supplier wants to reduce component and vehicle weight in the ever-present challenge to improve fuel economy.

Those same companies are working diligently to use natural materials and fibers that pose no threat to the environment.

When they can achieve both goals at the same time, well, that's called a strong business case.

AOC LLC, a resin producer based in Collierville, TN, has a type of sheet molding composite (SMC) that is so new it doesn't yet have a trade name.

Engineers and executives with AOC refer to the new product as “green low-mass SMC” and previewed it for customers at a special reception in Detroit hosted by the Automotive Composites Alliance during the recent North American International Auto Show.

The material is eco-friendly because a component of the resin is derived from biomass, rather than from petroleum, says James Plaunt, account manager for AOC.

About 30% of the resin consists of biomass, and the resin makes up about 30% of the material overall, Plaunt says. The rest of the SMC consists of mold release agents and other additives.

The new material is lightweight because the calcium carbonate filler has been replaced with microscopic glass spheres known as microspheres.

As a result, the new SMC reduces mass 30% in comparison with standard SMC. Plaunt says the new material has a specific gravity of 1.3, compared with 1.9 for standard SMC.

At the recent composites event, AOC displayed a standard SMC fender along with the same fender produced with the new material. The weight difference was immediately apparent to the casual observer.

AOC Business Manager Michael Dettre says the new material can be compression molded at lower pressures with less-expensive tooling made of aluminum or from lower-grade steel. Standard SMC, molded at higher pressures, requires more robust steel tooling.

Factored together, the new green low-mass SMC carries a 6% cost penalty. “But you get a 30% weight savings and a material that is more environmentally friendly,” Plaunt says.

The weight savings compared with steel is more dramatic, considering the new material is lighter than standard SMC, which is 30% lighter than steel.

“OEMs are very interested in it,” Plaunt says of the material. “One OEM has it in the lab right now for testing.”

The material cannot yet be molded in color, so painting is necessary afterward.

SMC, a rigid plastic that holds up well in high heat, has had several decades' worth of automotive uses since the material was invented in the 1960s.

In the 1970s, auto makers started using SMC to produce exterior body panels. Recent applications include the hood, decklid and fenders of the Ford Thunderbird; the bed of the Ford SporTrac SUV pickup; and fenders on the short-lived Lincoln Aviator SUV.

The bed of the Honda Ridgeline pickup is made of SMC and incorporates a unique in-bed trunk.

Less successful several years ago was General Motors Corp.'s Pro-Tec composite box. Although technologically relevant, GM's box was optional on the Chevrolet Silverado and expensive.

In recent years, SMC producers have supplied weight-saving components to large SUVs and pickups. As those volumes have plummeted, so have the fortunes of SMC producers.

That's why AOC is marketing its new material for use in any Class A exterior body panel for passenger cars.

“We can offer a lot of advantages for hybrid vehicles,” Dettre says. “If auto makers stick with standard conventional raw materials like steel, they will have to make the vehicle smaller to get the fuel economy and battery life they are looking for. If they want to save weight, SMC is certainly an option to do that.”

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