Still Too Exotic

Mercedes-Benz might have a carbon-fiber body for its McLaren SLR, but it is a long way from using the material in cars with volumes higher than a few hundred units per year.

The problem is the carbon fiber industry isn't oriented to the needs of the auto industry, says Patrick Kim, the Mercedes engineer in charge of composites. “Just looking at past successes and trying to optimize existing solutions does not reveal a clear, straight path to the massive use of carbon fiber in automotive that all fiber producers are waiting for,” says Kim in a paper prepared for a recent conference on the material in Germany.

“What is needed (are) radically new designs and processes…and an intelligent, thoughtful look into the drawbacks and serious, creative and sustained thought about how to get around them,” he writes. “In particular, the cost issue must be addressed explicitly.”

Carbon fiber is light and strong and absorbs energy in crashes in such a spectacular manner that all Formula 1 racecars are made with it. While steel absorbs 25 kJ per kilogram, carbon fiber reinforced composites absorb 100 kJ/kg, according to Lee Bateup, marketing manger for carbon fiber at French supplier Saint Gobain Vetrotex.

However, carbon fiber is not yet industrialized, and engineers rely on metals for their high-volume cars.

The price of the carbon fiber, itself, is one issue. It has fallen from $43 (€35) per kilogram several years ago to $15-$19 (€12-E15) today. Analysts don't expect it to go below $12 (€10) in the next five years because much of the cost is in the energy used to produce it, and energy costs are rising.

Prices for the material are volatile. Carbon fiber costs 10 times as much as glass fibers used in composite materials, says Bateup. When the fibers are woven into a fabric, the difference is even greater because the weaving machines operate at only one-tenth the speed of those making glass cloths. And material makes up only half the cost of a carbon-fiber part today, the rest being in the process.

Another barrier to adoption is that the processing technology is immature, Bateup says. “The waste is 35%-40% in typical applications,” in which a carbon-fiber fabric is impregnated with resin and formed in a mold, he says.

Preformed parts, in which the carbon fibers are formed into the shape of the part before it is put in the mold, is the next step, Bateup says. He believes the technology exists to do volumes of 10,000 units per year for structural parts.

A European Union-funded project to develop a carbon-fiber floorpan called TECABS (Technologies for Carbon Fiber Reinforced Modular Automotive Body Structures) concluded in August with mixed results.

The idea is that if a steel body-in-white could be replaced by a carbon-fiber “body-in-black,” cars could be 40% lighter. Complex shapes possible with the system would reduce the number of parts involved from more than 200 to about 60.

The TECABS organizers said the project “successfully validated its material, manufacturing, simulation and design technologies” to achieve a volume of 50 parts per day, or 10,000 per year, “one order of magnitude higher than currently feasible for long-fiber carbon composite structures in cars.”

However, the group says, the technology is “not yet ready for application in full-scale production of mass produced cars.”

Production cars on the road today with carbon-fiber bodies mainly are priced above $247,000 (€200,000) and produced in volumes of less than 500 units annually, such as the Mercedes-Benz SLR McLaren and the Porsche Carrera GT.

Many higher-volume cars use the material sparingly for trim and aerodynamic hang-on parts, and custom carbon-fiber parts are available on the aftermarket.