Back in the spotlight: composites move out of aluminum's shadow

Ford Motor Co. did more than simply make a flashy design statement in January when it introduced the compositeskinned GT90 supercar at the North American Intertional Auto Show. It also brought composite materials back into the spotlight after several years of standing in aluminum's shadow.

Automakers have been making flashy - and some not-so-spectacular - concept cars out of glass- and carbon fiber-reinforced materials for decades. During the past several years, however, many of the most interesting and exotic projects have been skinned in aluminum, from Audi AG's Avus to Ford's Synthesis and Chrysler Corp.'s Neon Lite, reflectin the light metal's growing popularity in production vehicles.

Thanks to a new U.S. government/industry quest to build an 80-mpg (2.9L/100 km) midsize "Supercar" by 2004, an infusion of government research money, and the belief that composites' sky-high costs can be reined in, composite research efforts have been reinvigorated. Automakers now are involved in development efforts for fiber-reinforced plastics - even carbon fiber materials - for everything from lightweight bodies-in-white to pickup truck boxes.

The Partnership for a New Generation of Vehicles (PNGV), the industry/government organization responsible for developing the super high-mileage vehicles, is especially interested in carbon fiber because it is the only material available tod that definitely can produce a midsize vehicle body that's 40% lighter. "Most of the weight savings will come from lightweight body and chassis components," says Tim Adams, PNGV director for Chrysler. "We can achieve some minimal weight savings using alternate materials in the powertrain, but those weight savings may be offset somewhat by the weight from additional equipment that will have to be installed."

In the past, carbon-fiber projects in particular have been considered exercises in futility because the matefial is so expensive and difficult to fabricate. When General Motors Corp. introduced its 81-mpg carbon fiber Ultralite concept family car in 1992, engineers warned that just the material cost for the monocoque body was $13,000, compared with about $700 for a typical body-in-white made of steel.

But material suppliers and PNGV officials are growing increasingly optimistic that the cost of carbon-fiber composites can be reduced from $18 to $20 per pound to $3 to $5 per pound over the next 10 years. Suppliers such as DuPont Automotive and Cambridge Industries already are developing fabricating processes for mass-producing a carbon-fiber-reinforced thermoplastic body-in-white that would weigh 50% less than a conventional steel body structure and potentially cost 25% less. A process for manufacturing the carbon fibers themselves at far less cost also is rumored to be in the final stages of development.

Much work also is being done on glassfiber reinforced composites, which not only can chop body weight by about 30% but cost only a fraction of the going rate for carbon fiber. Glass-fiber composite leaf springs are common on many GM high-volume vehicles, for instance.

These materials usually aren't lumped in the same category as "fiberglass" or sheet molding composite (SMC), because the reinforcing fibers are much longer and stronger, the resin often is not the same, and the process also is different.

Glass-fiber composites usually are produced by the resin transfer molding (RTM) process, also known as liquid composite molding (LCM). In this process fiber preforms are placed in a die cavity. The other half of the die is placed over it and liquid resin is pumped into the mold, permeating the glass material. Then heat and pressure are applied until the material cures.

No matter what the raw materials, results are the same: strong, lightweight parts.

Last December Ford unveiled an all glass-fiber composite minivan space frame. The only metal used in the design was in the front-end engine cradle.

The body structure consists of only six composite components: underbody, a cross-car beam, right and left body side panels and inner/outer roof panels. They are joined using an adhesive-bonding system that completely eliminates mechanical fasteners. The bonding system contributes to structural strength and speeds the production process, engineers say.

The prototype was a collaborative development between Ford and several suppliers. Excel Pattern Works molded the frame using continuous-strand mat preforms from Vetrotex CertainTeed Corp. and vinylester resin supplied by Ashland Chemical Co. Composite frame components are molded around a low-density foam core supplied by BASF Corp. and American Sunroof Corp.

The project mirrors an earlier program in which Ford created a glass-composite Taurus body using only five sections - replacing more than 400 steel parts that normally are welded and bolted together to make a conventional steel unibody.

The Big Three's Automotive Composites Consortium (ACC) currently is working on a related technology - structural reaction injection molding (SRIM) - to develop a lighter-weight box for pickup trucks. If that effort is successful, it will be expanded to develop an entire vehicle body-in-white using the SRIM process.

SRIM is similar to RTM, except that it uses two polymers that are pumped into the mold separately and then react with each other to form a solid. There are inherent advantages and disadvantages to the process, but the biggest hurdles are lowering cycle times and what experts call "fiber management": getting all the glass-fiber reinforcements to consistently line up the same way to ensure uniform strength characteristics.

Some bumper beams and other high-volume structural components already are being produced via the SRIM process, but lots of development work has to be done before more complex structures are achieved. The current molding cycle time for a complex SRIM structural part is about 10 minutes, says John Fillion, manager of organic materials engineering at Chrysler and an ACC board member. His goal is to drop that to 4 minutes over the next 2-1/2 years. "If we reach that, it could be a viable competing process for PNGV," Mr. Fillion says.

Nevertheless, all of this composite development activity hardly puts aluminum - or even steel - out of the picture (see accompanying story).

Underneath Ford's GT90 composite skin is a honeycomb aluminum sandwich monocoque tub reinforced with tubular-aluminum framing. What's more, the steel industry is expected to unveil a new light-weight body-in-white prototype this year that is at least as light as a glass-fiber composite version - and at a fraction of the cost. But at least composites now seem to be back in the battle.