Advanced Materials For Lightweighting Cars: Carbon Fiber Brings Strength and Stiffness
In this series, we’re examining various materials used in the construction of automobiles to try to gauge their contribution toward designing cars that will comply with new federal emissions standards. In part one, we examined new technologies in steel, and last week we weighed the value of aluminum. This week, we’re examining carbon fiber composites, also known as carbon fiber reinforced plastic (CFRP). This synthetic material is made from carbon fibers embedded in a polymer matrix.
Last week, we noted how aluminum entered the market from the high end, as a premium material that delivered improved performance, handling, and fuel economy. Carbon fiber seems to follow the same path. This summer’s launch of the BMW i3 electric car demonstrates a serious commitment on the part of the automaker to the use of carbon fiber.
BMW shaved an impressive 770 pounds off the car by using carbon fiber. Using the logic of mass decompounding, a lighter car requires a lighter suspension, which requires a smaller motor to accelerate, requiring a smaller battery to meet the range target (which for the i3 is 80 miles), making the car even lighter, requiring an even smaller motor, and so on.
As we have seen with aluminum, the use of more expensive materials can be justified to consumers in the context of continually escalating fuel prices.
The BMW i3 carries a sticker price of $40,000 and is probably not within most people’s definition of affordable. But government subsidies could reduce the price considerably. In addition, carbon fiber manufacturing is in its infancy, and as production begins to scale, prices should come down.
That’s what Toray, the Japanese carbon fiber producer, is counting on. The company has been aggressively expanding its facilities, having recently acquired a 20-percent stake in Plasan Carbon Composites Inc. of Wixom, Mich., a U.S. manufacturer and distributor of CFRP auto parts. Plasan uses material supplied by Toray in its proprietary, high-speed molding technology, and is the sole supplier of such CFRP body parts as hoods and roofs to U.S. luxury car manufacturers. Toray has also been acquiring companies in Asia and Europe, where they have a joint venture with Daimler A.G.
BMW’s adoption of CFRP material was largely driven by their move into electric powertrains, as a means of counteracting the impact of a battery pack weighing almost 1,000 pounds. That works out to 100 pounds of battery for every ten miles of range. This led to a clean-sheet design as well as a bold commitment to a new material possessing unique structural characteristics, manufacturing processes, and supply chain — with relatively little experience on the road.
That commitment began 10 years ago. The company has forged new partnerships with suppliers, vertically integrated a global supply chain, built new manufacturing facilities, and incorporated carbon fiber composite parts on previous vehicles.
That is why they can now produce an i3 body every 20 hours, which is hardly mass production, but it’s a start.
Why go to all this trouble to begin working with an unproven new material? In a word: properties. Carbon fiber composites have 10 times the strength of stainless steel or aluminum; their stiffness is equivalent to stainless steel (stiffer varieties are also possible) at a weight that is two-thirds that of aluminum. In many ways, it’s an ideal structural material.
The original idea for a carbon fiber car came from Amory Lovins at the Rocky Mountain Institute (RMI) who began developing a concept car called Hypercar in 1994. Lovins realized how little of the fuel consumed by a car (less than one percent) is actually used to move the driver. Most of the weight, he realized, was to support an engine capable of moving all that weight. He realized that the entire concept was incredibly wasteful. His search for a much lighter car led him to carbon fiber, which was already being used in race cars.
Race cars were virtually built by hand, so Lovins and his crew developed new carbon fiber production methods and formed a company called Fiberforge. The company went out of business this summer after almost 20 years, victim of the long runway required to get a new technology off the ground. The company had been sustaining itself on military contracts while waiting for the automotive business to pick up.
Hypercar took a dramatic, clean-sheet approach to car design. The entire structure consists of only 14 parts that snap together. Innovations extend from the tires to the headlights. The result: a five passenger, super-safe SUV that gets over 100 miles per gallon.
Why aren’t we seeing these in showrooms? The auto industry does not move quickly, and this is such a radical departure, it will take some time for these innovations to reach the mainstream market. Yet the move by BMW shows that some of these ideas are being taken seriously. Here in the U.S., the apparent success of Tesla also shows that it is possible for new manufacturing approaches to emerge from outside the Detroit establishment.
Carbon fiber parts are increasingly showing up as aftermarket parts, as wheels, spoilers, hoods and doors. But the BMW i3, a radical redesign à la Hypercar, is without doubt the biggest news. The car is constructed of two modules, an aluminum Drive module, which houses the powertrain, batteries and basic structure, and the carbon fiber Life module, which contains the passenger compartment. The result is 2,799 pound car, which despite the 80-mile battery pack, compares favorably to BMW’s 3,362 pound 328i. Among the innovative design features in this car is the fact that the rigidity of the Life module is sufficient that a B-pillar is not required.
The company is getting its CRFP material from a joint venture between BMW and the SGL Group (SGL Automotive Carbon Fibers) in Moses Lake, Wash.