Automakers have dreamed of using carbon fiber in mass production for decades. But sky-high raw material prices and painfully slow manufacturing cycle times meant that dream was always more like a fantasy. Not anymore. Several recent advancements mean that carbon fiber could soon play an important role in the automotive industry.
Carbon fiber has been used in race cars, exotic sports cars and in automotive aftermarket parts for years. But now automakers believe they’ve identified the path of how to use it in mass production, and do so by the second half of this decade.
There’s no one single breakthrough, but rather a combination of improvements that make this possible. And they’re coming just in time for automakers who face the daunting task of boosting their average fuel economy to 54.5 miles per gallon.
Most carbon fiber components manufactured today are made in autoclaves, essentially big ovens that bake those parts at intensely high temperatures and pressures. But the autoclave cycle-time needed to make, say, a hood, is 90 minutes. That may be good enough to make body panels, cross braces and other parts for a car like the low-volume SRT Viper. But it’s not nearly fast enough for mass production where cars are rolling off the line every 60 seconds.
A crucial bottleneck is the manual layup of carbon fiber, where sections are cut with scissors and laid into a mold by hand. It takes forever. The next big improvement will come from using robots to cut and place all the carbon pieces, as well as load and unload the molding machines.
Carbon fiber molders such as Plasan, which makes the body panels for the Viper, are just now starting to use an induction process where infrared heat is used instead of an autoclave. This cuts cycle times to only 17 minutes, good enough to boost volumes to 30-50,000 cars a year – a very big step forward, but still not mass to production levels.
Suppliers such as Dow Automotive are working on developing new resins that flow faster and at lower temperatures. They want a low viscosity resin that shoots into a mold like water, quickly getting into all the nooks and crannies, but then sets very quickly. They call it command cure. This will lead to cycle times of only 5 to 7 minutes, tantalizingly close to what’s needed for mass production. The new resins are being used in a process called Resin Transfer Molding, or RTM. It allows molders to place a carbon fiber mat in a mold, close it up, shoot in hot resin at high pressure, then take out a completed part.
You may have seen the carbon fiber wheel that recently debuted at the SEMA Show, made by an Australian company called Carbon Revolution. Though company officers will not disclose how the wheel is made, they admit it’s very similar to the RTM process.
Making carbon fiber is complicated but fairly straightforward: You take a fiber and heat it up until it carbonizes. But automakers use an aerospace-grade carbon fiber called polyacrylonitrile (PAN), which has a level of purity that greatly exceeds what’s needed for automotive applications. At roughly $15 a pound (steel is less than 40 cents per pound), it’s another reason why carbon fiber is so expensive. But it’s the only carbon fiber available, so that’s why they use it. The Oak Ridge National Laboratory, which is doing some of the most advanced research in this field in the US, is looking at using different materials, notably polyethylene, which is significantly cheaper. Oak Ridge is also experimenting with lignin, which offers the intriguing possibility of making carbon fiber from bio-mass. And with the abundance of natural gas now available in the US, it’s also looking into making carbon fiber with that.
Another part of Oak Ridge’s work is developing Computer Aided Engineering (CAE) tools for engineers to predict how their carbon fiber designs will perform. Amazingly, those tools aren’t available yet. Other research includes USCAR, the US Council on Automotive Research, which is delving into how to make cost-effective floorpans and frame rails.
Developing carbon fiber components for mass production means designing them to fit into the existing automotive manufacturing infrastructure. If these are structural components that go into a car early in the assembly process, they will need to withstand the electro-coat and 400º F bake ovens in assembly plants without warping or losing strength. Structural adhesives will have to replace welding operations, and there won’t be any “metal finishing” to smooth out any blemishes. The point is, you can’t just start using these pieces in a car without thinking through the entire manufacturing process.
Now automakers are focused on developing cycle times that are well under 5 minutes, a key enabler for mass production. And everyone is getting in on the game. Toyota, Daimler, Subaru and Nissan have agreements with the Japanese company Toray, the largest carbon fiber supplier in the world. Ford is teaming up with US-based Dow, while General Motors recently signed an agreement with Teijin, another Japanese company. BMW formed a joint venture with the German supplier SGL. Indeed, BMW claims it will be the first major automaker to sell an all-carbon car, its electric i3.