European carmakers including Lamborghini, Ferrari, Bentley and McLaren made carbon-fiber composites the standard for high-end supercars.
Now those same companies are taking carbon fiber even further, creating new ways to process it that will reduce the amount of time needed to mold the composite, and push it even further into structural parts.
Automobili Lamborghini SpA even made its new technology the centerpiece of its Sesto Elemento concept car introduced Sept. 30 at the Paris Motor Show. The car uses carbon fiber for the passenger cell, the front and rear-end structures, suspension components, the interior, all exterior panels, suspension components and the propeller shaft. Even the tailpipe is made from a carbon and glass-ceramic composite.
The new thrust, said Stephan Winkelmann, president and CEO of Lamborghini, is part of an effort to reduce weight significantly, pushing performance even further than its 570-horsepower engine can do on its own.
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.
And Lamborghini is not alone in taking carbon fiber further. During the Society of Plastics Engineers' 2010 automotive composites conference in Troy on Sept. 15 and 16, engineers from Lamborghini were joined by engineers from Bentley Motors Ltd. 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. Surrey, England-based McLaren has been focusing on liquid-resin infusion.
BMW AG of Munich has developed its own carbon-fiber processing technique that it will use on its future Megacity Vehicle electric car.
Lamborghini which has been working with Boeing Co. engineers at its Advanced Composite Structures Laboratory in Seattle as well as running its own Advanced Composite Research Center in Lamborghini's home town of Sant'Agata, 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. Lamborghini also has signed a development agreement for carbon fiber with golf-club maker Callaway Golf Co. to expand the technology further.
The process, which Lamborghini calls forged composite, is far faster than traditional hand lay-up prepreg and autoclave processing, he said. That system could produce a maximum of four passenger cells called a monocoque 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 RTM 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 like the monocoque and the front and rear structural cells. ( Lamborghini calls these cells the cofango, combining the Italian words cofano or hood, and parafango or fender.)
Using an RTM light method with low pressures, vacuum assist and carbon tooling still will require the investment in injection presses it has more flexibility in tooling than traditional RTM while still speeding up production, Feraboli said.
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 comes in at a total of 2,202 pounds compared to the current-model Gallardo LP Superleggera's 2,954 pounds.
While the Sesto Elemento is a technology study car, Winkelmann said it is a clear indication of where Lamborghini will take carbon fiber.
Systemic lightweight engineering is crucial for future super sports cars, he said in 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, based in Crewe, England, has focused on ways to speed the hand layup of carbon-fiber parts, said Antony Dodworth, principal research manager with Bentley Materials Technology.
We need to automate, he said. We cannot afford to continue with prepreg processes as it is.
The process, called directed carbon-fiber pre-forming, adds a very small amount of cobalt to the carbon fiber. The company can then 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.