BMW leading the way in carbon fiber auto bodies

According to the online version of Automotive Engineering by SAE, BMW’s MegaCity EV program is driving design, process, and materials technologies that will help push the strong, lightweight composite closer to the automotive mainstream.

Fact is BMW is already crash testing a prototype body-in-white using carbon-fiber materials.

Body in White or BIW refers to the stage or progress of automotive manufacturing in which the car body sheet metal (including doors, hoods, and deck lids) has been assembled or designed but before the components (chassis, motor) and trim (windshields, seats, upholstery, electronics, etc.) have been added.

The name is derived from manufacturing practice before steel unibody or monocoque bodies when autombile bodies were made by outside firms on a separate chassis with an engine, suspension, and fenders attached. The manufacturers built or purchased wooden bodies (with thin, non-structural metal sheets on the outside) to bolt onto the frame. The bodies were painted white prior to the final color.

The MegaCity EV’s body-in-white, currently in development, features a monocoque “safety cell” designed for passenger protection. According to resources quoted in the article, BMW calls the four-seater structure LifeDrive. 

Furthermore, it uses carbon-fiber-reinforced plastic (CFRP) material developed in collaboration with SGL Group. For the record, CFRP is 50% lighter than steel for a given component, with superior strength and rigidity. A photo of the body for BMW showed a one-piece windshield frame that traditionally would require multiple metal stampings to be positioned in a fixture and spot welded.

EVs Demand Less Weight

Everyone in the auto industry realizes that down weighting the automobile is the best way right now to attain the efficiency needed for EVs. That explains why BMW engineers are using the CFRP body in combination with aluminum chassis components, which will offset up to 772 lb (350 kg) of additional mass related to the car’s 96-cell lithium-ion battery packs, wiring, and electrical components.

Engineers in the auto industry are also aware that cost and process cycle times are two of the major hurdles in implementing carbon fiber beyond premium-priced niche applications. Fact is traditional carbon-fiber processing is expensive, because it has been a slow, manual-intensive operation, where carbon-fiber mats are joined to their thermoset-polymer resin matrices.

The key to reducing these costs is obviously automation. Success there, though, centers on first consolidating components in the design stage so the overall bill of materials is reduced.

This is why there is a connection to the aerospace industry and Boeing, which is already using carbon fiber materials. This is also why SGL Group, a German company, has been chosen as a working consultant for BMW. The company already weaves the fibers into fabrics that can be molded into components, where fiber mats are oriented in specific directions in the mold to provide strength. For the record, the company is building a $100 million plant near Seattle, WA, near Boeing’s primary engineering and production facilities to produce components for the MegaCity.

Where is Michigan in all of this? Considering the fact that BMW is not alone in attempting to bring carbon fiber to high volume production, Michigan is not exactly touting its home-grown expertise; at least not yet. Daimler and Toyota have their own projects, but GM and Ford appear to be mum on the subject.

Examiner Final Comments

I well remember there was a skunk works program at Saturn led by Hulkie Alducatti, before the engineers and designers were pulled back into GM. The team investigated the use of aluminum, rivets and adhesives for lighter-weight under bodies, chassis components and body-in-white. Somewhere along the way, though, the program seemed to have died, except where used in advance prototype builds.

Carbon fiber, on the other hand, is often used by after-market suppliers, as with carbon-fiber hoods, etc. for Camaros and Mustangs. Some parts are being made for chassis components. Obviously, these parts command premium prices due to their low volumes and manual-intensive processes. Applying carbon fiber to an entire body-in white, for example, would require another level of sophistication in concert with the most-important element - high-volume production.

Fact is, the steel industry is not sitting on its hands either. High-strength steel is increasing, and is still the best material from a cost standpoint, a functional standpoint, as well as from a mass standpoint for particular applications. Lotus Engineering, for example, conducted a study replacing mild steels with high-strength steels in the body in white (BIW) of a crossover utility vehicle—a 2009 Toyota Venza. The HSS-intensive BIW was about 16% lighter—and 2% cheaper.

In the case of an EV, though, a 16% lighter body using high-strength and ultra-high-strength steel is in the right direction, but still not enough.