Greentech
Carbon Fiber, Light and Strong, Arrives Where It’s Most Needed
...Unless you drive in a neighborhood frequented by millionaires, you may never have seen a car made of carbon-fiber composites, though they have been on the road for more than two decades.
The reason is simple: the models available with carbon-fiber structures are mostly exotic sports machines from makers like Ferrari and Lamborghini that carry price tags well into six figures. The situation will be different next year, when BMW’s electric city car, the i3, goes on sale in the United States — for roughly the price of the company’s 3 Series models, which start at about $33,000.
Carbon fiber’s high strength and low weight make it ideal for applications where the finished product needs to be as light and strong as possible. Jetliners and fighter planes, made in small numbers where the material’s slow and complex production process is not such an impediment, use these composites extensively. Designers of racecars and high-end sports gear turn to carbon for the same properties.
Until recently, however, there was no way that cars with everyday price tags could contain substantial amounts of carbon fiber. Electric vehicles in particular would benefit, as the weight reduction would translate into longer driving distances on each battery charge.
That is how BMW ended up plunging far deeper into the lightweight materials world than executives might have expected a decade ago when the company started making carbon-fiber roof panels for the high performance M3 CSL. Now BMW is not only producing carbon-fiber body structures for the passenger cell of the i3 E.V. — first shown as a design study in 2011 and due to be presented to the media in Germany this week — but it will manufacture the basic material itself. This is something of a throwback to Ford making its own steel in the Model T days.
BMW took the initiative because it saw little progress from carbon-fiber suppliers in bringing the material’s cost low enough for mass-production cars. The automaker says it can supply carbon fiber to the i3’s highly automated assembly line in Leipzig, Germany, at about one-third the market price per pound. The sporty i8 plug-in hybrid will also take advantage of the technology.
...Designing the i3 body with a passenger cell of carbon fiber and a lower “drive module” of aluminum saved about 550 pounds compared with a steel structure, helping to wring the most miles from the battery. BMW says the car will have a range of 80 to 100 miles; a 2-cylinder range-extender engine will be optional.
...Even though the carbon-fiber material is still much more expensive than steel, differences in the overall bodymaking process yield cost savings that help to offset the cost. For starters, the i3 body structure uses just 130 carbon-fiber pieces, compared with about 400 for a steel body. The smaller number is partly explained by the ability of engineers to design very complex parts for the molding process that would not be feasible with the huge stamping presses and dies used to make steel parts. Often a single complex carbon part can replace four or five metal parts that would be welded together.
“We can produce an i3 in about 20 hours, versus about 40 hours for a 3 Series car and using just one-half the space needed for a steel body shop,” said Daniel Schaefer, who oversaw development of the i3 production process...
