High-end makers keep expanding use of carbon fiber

European carmakers such as Lamborghini, Ferrari, Bentley and McLaren made carbon-fiber composites the standard for high-end supercars. Now they're taking carbon fiber even further, creating new ways to reduce molding time and get more of the material into structural parts.

Automobili Lamborghini S.p.A made its new technology the centerpiece of its Sesto Elemento concept, which was introduced September 30 at the Paris auto show.

The car uses carbon fiber for the passenger compartment, the front and rear-end structures, suspension components, the interior, all exterior panels, and suspension components.

Even the tailpipe is made from a carbon and glass-ceramic composite.

The new thrust, said Stephan Winkelmann, CEO of Lamborghini, is part of an effort to slash weight and push performance.

"The Sesto Elemento shows how the future of the super sports car can look," Winkelmann said. "Extreme lightweight engineering, combined with extreme performance, results in extreme driving fun."

"It is our abilities in carbon-fiber technology that have facilitated such a forward-thinking concept."

Others active, too

And Lamborghini is not alone in taking carbon fiber further. During the Society of Plastics Engineers' automotive composites conference in suburban Detroit last month, engineers from Lamborghini were joined by engineers from Bentley Motors and McLaren Automotive in talking about new production techniques for carbon fiber.

Bentley has added cobalt to its carbon fiber to make it magnetic, and is using magnets to automate the layup process, which speeds production and cuts costs. McLaren has been focusing on liquid-resin infusion.

BMW AG has developed a carbon fiber processing technique that it will use on its future Megacity Vehicle electric car.

Lamborghini--which has been working with Boeing engineers at its Advanced Composite Structures Laboratory in Seattle and runs its own research center in Italy--is focused on advanced compression molding using short carbon fibers in a low-pressure injection mold, said Paolo Feraboli, director of the structural carbon-fiber research group.

Working with Callaway

Lamborghini also has signed a development agreement for carbon fiber with golf club maker Callaway Golf  to expand the technology.

The process, which Lamborghini calls "forged composite," is far faster than traditional hand processing, he said. That system could produce a maximum of four passenger cells, called monocoques, per week, which is too slow even for a low-volume producer.

Lamborghini considered vacuum-assisted resin transfer molding, similar to the process used for yachts and other marine structures, but it had problems with variable thickness on mold lines.

Traditional resin transfer molding provided consistent thickness and a controlled shape, but requires an expensive machine and large and expensive tooling, and it would be difficult to achieve large parts such as the monocoque and the front and rear structural cells.

Using a method with low pressures, vacuum assist and carbon tooling still will require investment in injection presses.

The new process has more flexibility in tooling than the traditional resin transfer molding system and speeds up production, Feraboli said.

30 percent lighter than aluminum

Lamborghini's experiment using compression molding with a carbon fiber sheet molded compound produced a structural suspension part that was 30 percent lighter than an aluminum part, and its three-minute cycle time beat both traditional carbon-fiber and aluminum processing, he said.

The Sesto Elemento concept car weighs 2,202 pounds, about 750 pounds lighter than the current Gallardo LP Superleggera.

Winkelmann said the Sesto Elemento is a clear indication of where Lamborghini will take carbon fiber. "Systemic lightweight engineering is crucial for future super sports cars," he said while introducing the car in Paris.

"We will apply this technological advantage right across our model range."

Its high-end competitors will be on the same track.

Bentley has focused on ways to speed the hands-on production setup for carbon-fiber parts, said Antony Dodworth, principal research manager with Bentley Materials Technology. "We need to automate," he said.

The process, called "directed carbon-fiber pre-forming," adds a very small amount of cobalt to the carbon fiber. The company then can robotically shoot a fine stream of carbon fiber into a magnetized mold at a rate of 6 kilograms per minute.

"The robot can achieve that delivery all day, every day," he said.

Bentley compared its automated system to a bumper system for a race car that takes a day and a half with hand labor, Dodworth said. Its new process completed the layup in 20 minutes.

The company already has used the process in a structural carbon-fiber spare wheel well on its Mulsanne sedan.

(Source: Automotive News)