BMW: Carbon fiber in 2013

BMW plans to begin high-volume production of carbon fiber parts in two years, making it a strong contender to be the first automaker to move beyond limited-edition use of the exotic material.

But Daimler, which has taken steps aimed at making carbon fiber parts in 2012, is among the automakers racing toward the same goal.

In 2013, BMW will start building the i3 electric car, a vehicle that features a passenger cell--the protective shell around the passenger compartment that ensures the integrity of the vehicle in a crash--made of plastic reinforced with carbon fiber. BMW will produce about 30,000 i3s a year, according to Automotive News Europe.

BMW declined to confirm likely production volume for the i3. But Joerg Pohlman, managing director of the joint venture that produces BMW's carbon fiber, said BMW can make tens of thousands of vehicles.

"We have developed a very flexible production plan," Pohlman said in a telephone interview. "We are prepared to manufacture many more cars if demand is higher than our conservative estimate."

If so, the i3 will be a major breakthrough: a carbon fiber-intensive vehicle produced in volume at a moderate price.

Cutting costs
In 2010, BMW formed a joint venture with SGL Group of Germany to produce carbon fiber reinforced plastics for electric cars.

In the third quarter of this year, a factory in Moses Lake, Wash., will start producing carbon fiber thread, which will be shipped to Germany for conversion into the fabric used to make parts.

To cut costs and allow mass production, the partners are working to perfect a process called resin transfer molding.

The carbon fiber fabric is placed in a mold, and resin is injected under high pressure and temperature. The process, which once took 20 minutes per part, now requires less than 10 minutes. Robots cut and handle the material and components, which previously were made by hand.

The robots will help BMW achieved big savings. A pound of carbon fiber now costs only a third as much as a pound used in the M3 CSL coupe's roof when the limited-edition car was introduced in the 2004 model year.

More automation
"For the M3, we could afford to have a few workers put the parts in the form," Pohlman said. "We were only making a few thousand a year. But now we'll be making tens of thousands of parts. So there is a whole lot more automation."

BMW is not the only automaker that plans to use carbon fiber. Last year Daimler announced plans to form a joint venture with Toray Industries, the world's largest producer of carbon fiber.

In January, Daimler said the partners will use carbon fiber and other lightweight materials to reduce the weight of a vehicle's body-in-white by 10 percent. Daimler also indicated the partners will produce components for cars to be launched in 2012. Daimler did not indicate which models would feature carbon fiber, but hinted it would use carbon fiber in the vehicle's passenger cell.

Machining Injection Molds with Ultrashort Laser Pulses

Systems for homogeneous LED lighting have in the past used a large number of LEDs and optical diffuser panels for distributing the high spot-luminance. As an alternative, ever compacter optical waveguides, adjusted to the lighting requirements, are increasingly being used, in which the light is diverted and distributed with refractive outcoupling by roughening or structuring. Refractive light outcoupling is performed with microlens arrays. Such an array may consist of several hundred thousand microlenses with geometries in the micrometer range. Producing such structures by injection molding requires a high, uniform quality. It is determined by the precision of the molds.

At the Fraunhofer-Institute of Laser Technology (ILT) Aachen, Germany, injection molds were machined with ultrashort laser pulses. This could significantly improve the process. New, industrial ultrashort pulse lasers reduce machining times to a few hours, compared with conventional methods, which take at least a week. Moreover, the ultrashort pulse lasers permit high precision for machining steel molds. The picosecond laser pulses are about a thousand times shorter than a conventional quality-switched solid-state laser, like that used, e.g., for marking. While melt expulsion still occurs with conventional lasers, the ultrashort pulse laser evaporates the material with high precision and no residues. Subsequent laser polishing permits a smooth and uniform surface on the molds down to the submicrometer range (Ra > 100 nm).

For the tests, commercial systems with a focus diameter of 20 µm, several 10 µJ of pulse energy and a repetition rate of >100 kHz were used. The mold insert microstructure generated by laser texturing has depressions with a diameter of 50 µm and more. While commercial systems have so far only been available in the range below 100 W, prototypes of over 1,000 W average output have already been developed at the Fraunhofer ILT.