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Carbon fiber enters the materials mix

Monday, December 7, 2015 - 09:00
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New materials are increasing in U.S. vehicles as automakers strive to meet new emissions standards by reducing the weight of their cars. While most of the focus so far has been on high-strength steel and aluminum, body shops could soon be seeing more carbon fiber composites as well, and that could require an investment in new tools and training.

Carbon fiber has largely been used in aerospace applications, but isn't completely new to automotive. Lamborghinis and Ferraris, for example, include carbon fiber infrastructure, but most body shops are never going to see those cars in their bays. Now, however, Fiat Chrysler is adding a carbon fiber to its Alfa Romeo 4C, which will have an all carbon fiber chassis. BMW's 7 series and the Corvette Z06 also have carbon fiber parts.

As a result, Chrysler has begun offering carbon fiber repair training for its body technicians. "They were concerned about being able to do damage repair, and needed help developing those repair techniques," says Mike Hoke, president of Abaris Training Resources in Reno, Nev. Hoke's company has been training technicians in the aerospace industry how to repair carbon fiber panels for years. Now, the company also offers similar training for the auto repair industry.

(Photo courtesy of Abaris) A carbon fiber repair on an aircraft panel

In fact, Hoke led a demonstration at the 2015 SEMA show, explaining the basics of carbon fiber repair. While the presentation was relatively brief, it included an overview of damage removal and taper-scarfing operations, a hands-on demonstration of how to lay up an adhesive film layer and carbon fiber repair plies, and vacuum bagging of the repair for curing the epoxy resin.

It's unclear yet how common these repairs may be. If a tub gets damaged on a high-end car, the car will likely be totaled. "But there are gray areas where it is conceivable on a side impact that the you could damage the tub in the rocker box area, but its not worth totaling the whole car," Hoke says.

Right now, Chrysler is following Lamborghini's model, in which a team of highly trained technicians is available to repair the carbon fiber structure on site for a fee. In Chrysler's case, though, there is some demand from high-end body shops in certain regions (California, for example) for similar training. Abaris offers three classes that, once completed, will qualify a technician to complete those structural repairs.

"The automotive side of our business is small but increasing, and the rate of that increase is going to be pretty rapid, because the material is getting cheaper and there is more pressure to reduce weight," Hoke says.

According to Hoke, most of the tools and equipment used in carbon fiber repairs will be familiar to body shops. The one key difference is the need for vacuum bagging because the repairs have to be cured under vacuum pressure. "The pump needed can be the same kind used for air conditioning systems, but with different fittings and hoses," Hoke says. "Those repairs also have to be cured at elevated temperatures, anywhere from 150 degrees to 250 degrees, depending on the material and epoxy."

The heat has to be applied evenly. For complex parts, that also requires some specialized heat controlling equipment, which may cost as much as a few thousand dollars.

Cutting the material also requires a different approach. You can't cut carbon fiber with a jigsaw or reciprocating saw because you could delaminate the edge of the cut. "You use cut-off wheels, circular saws or band saws, and you can't use blades with teeth," Hoke says. "You need grit edge or diamond grit blades."

Drilling the material also requires specialized bits, along with a high-speed/low-feed approach.

The material itself is expensive, and is generally only available in very large quantities. While it can be stored, carbon fiber does have a limited shelf life; if you buy a large quantity and don't use it, it will eventually have to be scrapped or recycled. "There are some companies now that specialize in selling small quantities, but if the 4C is successful, then Chrysler will likely have to establish a mechanism to provide shops with material for these repairs," Hoke says.

Overall, Hoke says the biggest challenge in learning how to repair carbon fiber components is the number of small, detailed steps necessary to make the repair correctly. "All of these repairs are adhesively bonded, and the surface prep before the bond is critical," Hoke says. "If you don't get that right, the repair will peel off. It's very different than just slapping a patch on a fender, but almost anybody who can do body work can be easily trained to do this."

For the time being, though, carbon fiber repairs will likely remain in the realm of higher end shops. The 4C is the lowest-cost model available with carbon fiber at $65,000. Using the material in cheaper cars is generally not seen as cost effective.

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