Carbon fibre-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 forced 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.
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 a purely electric car increases by some 250 kilograms, while for a plug-in hybrid it’s around 200 kilograms.
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 fibre 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 boot by the end of 2012,” he says. Cost is an issue, but Sellergren says that even though it is still considerably more expensive than steel and aluminium, the future still lies in composites for electric and hybrid cars.
According to Volvo’s calculations, the cost of a bonnet made of the new battery material could be equal to that of an original bonnet plus a lithium-ion battery. “As manufacturers, we could add on an extra amount for the carbon fibre bonnet, 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.
Audi, by virtue of the aluminium car A2, is a forerunner in lightweight car manufacturing. In the company’s “lightweight” centre in Neckarsulm, in southern Germany, Audi engineers build on the carbon fibre 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 120,000 euros and is only made at a rate of about 15–20 per day, Audi uses carbon fibre-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 aluminium components could be replaced by a single carbon fibre 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, fibres are packed into a composite material to increase the weight advantage in comparison with aluminium, 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 aluminium. 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 kilogram 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.
The Audi R8 Spyder sports car uses carbon fibre-strengthened polymer in both the sides and the top of the roof box.
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 aluminium 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 fibre 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 fibre. The aim is that within three years the company will be developing components made of carbon fibre 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 US dollars in a composite factory in Moses Lake, Washington, in the United States. 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 fibre, which is used today in racing cars at a cost of USD 22 to 55 a kilogram.
The carbon fibre will be made on two lines, with an annual capacity of some 1,500 tonnes, 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 travelling more than 100 kilometres 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 200 kilometres an hour.
Megacity is expected to roll off the production line in 2013–2014 in Leipzig, where BMW has invested more than EUR 400 million. According to BMW, it will be the world’s first production-line car with an entire passenger cell made of light carbon-fibre composite on an aluminium chassis. The first sketches that BMW has released reveal a car that looks straight out of a science fiction movie, with a battery 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 a auto conference in Nuremberg 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.”
Assembly line production poses a major challenge for future cars.
24
million hybrid or electric cars will be sold annually by 2025.
35%
of new cars will run on fuel only by the year 2025, according to estimates.
Carbon fibre
Composites that are used in the aerospace and car industries are mostly made of epoxy or vinylester that are reinforced with carbon fibre. The advantages of these composites are their low weight and mechanical properties such as high tautness. Carbon fibres split easily, but they can also be formed to absorb high amounts of energy. This is necessary in racing cars, which are in danger of head-on collisions at high speeds.
Less-advanced fibre-reinforced plastics have long been used in the car industry. In the former East Germany, more than 3 million Trabants were made from duroplastic, consisting of Soviet Union cotton and phenolic resin from chemical factories.
TECHNICAL INSIGHT
Plenty of uncertainty
Composites in the aerospace industry are already a growth market. Sandvik Coromant has many tool solutions on 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 fibre 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 stage,” 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 drillshave a diamond surface, which improves the hole quality and performance of the users’ machines.
Composites are already being used in Formula One racing cars. The challenge is to bring the technique into the mass production of private cars.
How to turn a car body into a battery
Volvo Cars’ solution for lighter electric cars is simple: Instead of installing heavy batteries, the company hopes to be able to turn the whole car body into a battery. That can save up to 250 kilograms of weight, and every kilogram is crucial when it comes to making electric cars work for real. In the centre of this new technique is the use of new composite materials. This is how the solution works:
This article was first published in the Sandvik Coromant customer magazine, Metalworking World.
