Carbon fiber-based composite materials are expected to play a key role in the search for lighter cars, despite huge challenges in production line manufacturing.
Tighter environmental demands and the ever-growing car use in developing cities have force the automobile industry to think in new ways. In focus are lightweight new body shapes and battery lifetimes, in the form of either hybrid or purely electric cars.
By 2014 at the latest, almost all car manufacturers will offer hybrid cars, and that is just the beginning. Ferdinand Dudenhöffer, professor and head of the Center for Automotive Research at Duisburg-Essen University in Germany, talks of a change in technology.
“By 2025 the share of new cars running on fuel alone will have dropped to 35 percent globally,” he says.
Hybrid and Electric Sales on the Rise
Another forecast states that within 10 years, some 24 million hybrid or electric cars will be sold annually. This figure, says Dudenhöffer, is conservative. All automakers will be wrestling with the same problem, though — weight. When a battery is installed, the weight of purely electric car increases by some 550 pounds, while for a plug-in hybrid it’s around 440 pounds.
Volvo Cars is working on a possible solution. Together with researchers at Imperial College London’s Department of Aeronautics, engineers in Gothenburg, Sweden, have come up with a composite material made from a mixture of carbon fiber and polymer that is capable of charging and storing energy. The idea is that Volvo cars of the future will have a body that, in effect, acts as an electrochemical battery. But how far away is such a solution?
Per-Ivar Sellergren, development engineer at the Volvo Cars Materials Center, is optimistic. “If everything goes according to plan, we will have a prototype in the form of a car trunk by the end of 2012,” he says. Cost is an issue, but Sellergren says that even though it is till considerably more expensive than steel and aluminum, the future still lies in composites for electric and hybrid cars.
According to Volvo’s calculations, the cost of a hood made of the new battery material could be equal to that of an original hood plus a lithium-ion battery. “As manufacturers, we could add on an extra amount for the carbon fiber hood, because we are, in effect, getting a battery for nothing,” he says.
According to Ulf Carlund, Volvo Cars’ composite expert, until now production methods have been too slow, and earlier investments in traditional auto plants have needed to be exploited. Partly, it is also due to the fact that traditional steel automakers have found it difficult to think and work with composites. However, there is a strong will to change, and the public will see more and more polymer materials on the inside and outside of new cars, according to Volvo experts.
Research and Development
Audi, by virtue of the aluminum car A2, is a forerunner in lightweight car manufacturing. In the company’s “lightweight” center in Neckarsulm, in southern Germany, Audi engineers build on the carbon fiber techniques already used by subsidiary Lamborghini as well as on composite technology/expertise developed by parent company Volkswagen’s luxury Bugatti model.
In the Audi R8 Spyder sports car, which costs more than $170,000 and is only made at a rate of about 15-20 per day, Audi uses carbon fiber-strengthened polymer in both the sides and the top of the roof box. One prerequisite that would make it more cost-effective in cheaper mass-produced cars is that a number of aluminum components could be replaced by a single carbon fiber component. “Instead of five or six different tools, maybe you would only need a single tool,” says Karl Durst, a development engineer at Audi’s Leichtbauzentrum.
Here, among other projects, fibers are packed into a composite material to increase the weight advantage in comparison with aluminum, from around 17-18 percent to about 25 percent. The project hinges on a material that has the same drag and press weight burden capability as aluminum. Despite this, there are still several major and minor problems to solve, says Durst, not least the corrosion in the joints between composites and other materials. There is also a noise factor. For every pound that the car becomes lighter, the noise level increases, requiring insulation, which in turn adds more weight. Another challenge will be the material’s familiarity among car mechanics handling it. “It should be possible to fix the car and replace composite car parts in even the smallest Audi workshop anywhere in the world,” says Durst.
Companies with Smarter Manufacturing
The manufacturing process needs to be improved. Lars Herbeck, who is manager of German machine manufacturer Voith’s subsidiary Voith Composites, foresees a large need in several areas. One is with the optimized flow processes for materials, and another is a paced production of more than 100,000 components a year, as well as a much faster pace in the cycle. Compared with aluminum components, which can be made every second, it can take from 20 minutes to an hour for larger composite parts. This works in the aerospace industry but not in the auto industry’s large-scale assembly line production, which turns out more than 55 million cars a year globally.
Oliver Geiger, who is a researcher in the composite materials department at research institute Fraunhofer,-Institut für Chemische Technologie in Pfinztal, Germany, is looking at ways to get large companies to work together in various sectors. Audi’s Durst talks of the need for a leap forward in the technology, rather than relying on a slower evolutionary development.
Daimler too, which has used carbon fiber in its racing car, the SLR McLaren, since 2004, is also concentrating heavily on developing the technology. In April 2010, it started a cooperation with Japanese chemicals company Toray, the world’s leading manufacturer of carbon fiber. The aim is that within three years the company will be developing components made of carbon fiber for models with an average manufacturing volume of 20,000 to 40,000 cars a year.
Meanwhile, archrival BMW is being considerably braver. Together with German partner SGL Carbon, BMW is investing $100 million in a composite factory in Moses Lake, Washington. According to BMW Head of Finance Friedrich Eichiner, the factory will make “large volumes at competitive prices” for the first time. The aim is to reduce the price of materials to less than half of the current price of carbon fiber, which is used today in racing cars at a cost of $10 to $25 a pound. The carbon fiber will be made on two lines, with an annual capacity of some 1,600 tons, and will be used to make the new BMW electric car, the Megacity Vehicle, a four-seat hatchback with a 35 kWh lithium battery, capable of traveling more than 60 miles on a charge. A sports car variation, with a small additional diesel engine and two electric engines should be capable of reaching a top speed of more than 120 miles an hour.
Megacity is expected to roll off the production line in 2013-2014 in Leipzig, where BMW has invested more than $565 million. According to BMW, it will be the world’s first production-line car with an entire passenger cell made of light carbon-fiber composite on an aluminum chassis. The first sketches that BMW has released reveal a car that looks straight out of a science fiction movie, with a batter like a flat mattress under the whole coupe, over-dimensioned wheels and a dynamic, almost aggressive image.
It remains to be seen what the effect will be on the factory floor of an industry already under pressure. “It’s a gamble,” says a lightweight specialist at one of BMW’s competitors.
Manager Norbert Reithofer is also fully aware of the risks. At an auto conference in Nuremburg in October 2010 he said: “It’s possible we won’t make any money during the first production cycle with this technology, but then it will be subsidized by traditional techniques.”
Technical Insight - Plenty of uncertainty
Composites in the aerospace industry are already a growth market. Sandvik Coromant has many tool solutions to offer in this area, including PCD (polycrystalline diamond) and carbide drills. In the auto industry, however, there is still plenty of uncertainty over what kind of need there will actually be for composites.
Carbon fiber technology is certainly already established in Formula One racing cars and expensive luxury and sports cars. But these are cars that are made more or less manually in very small numbers.
“When it comes to mass production we are still at the research and development state,” says Francis Richt, who works with composite development at Sandvik Coromant. “But we are counting on this new material soon being used to reduce the weight of electric and hybrid cars.” Richt adds that the appliances in the aerospace industry are more complex than in vehicles, with a greater necessity for quality and with simultaneous processing of composites and other materials such as titanium.
“We know that cars have a more homogenous structure than planes, which, for example, reduces the need to drill thousands of holes and mill large areas,” says Richt. “On the other hand, there is a need to be prepared to open up other holes and cavities. Nevertheless, we see other demands in automotive compared to the very advanced aerospace industry.”
There are tools existing today that can be used in the car industry. For example some Sandvik Coromant CoroDrill drills have a diamond surface, which improves the hole quality and performance of the users’ machines.
Originally published in Metalworking World 2.2011, a business magazine published by Sandvik Coromant.
Text: Tomas Lundin