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Working with carbon fiber is similar to fiberglass, with a couple of differences. The fibers are quite a bit stiffer (usually 5x-10x), so the drape of the material is not as good as with glass. Carbon fiber is much more expensive than glass, so you can't afford too much waste, so one generally makes more precise patterns and is more cautious. Carbon fiber is generally available in tape and cloth forms, so wet lamination is usually the cheapest and easiest method to use. I have never seen CSM (chopped strand mat) typically used in carbon (doesn't mean it doesn't exist). There are also aerospace grade carbon materials (prepregs) but nobody would use these for auto parts due to the expense.

The process is used is same as constructing boats. First, a master of the part being created is needed, usually either an original, or a mockup. I have seen plaster and mahogany used for this. Then, a mold is created, by applying mold release to the master and coating the outside of the part with the material used for the mold. There are a variety of options for this, and generally depend on how many parts will be made from the mold. Again, this can be plaster like material for one off parts to fiberglass for a mold which will be used over and over. Once the mold has cured it is separated from the master, trimmed and then is nearly ready for use. The mold is prepared for use, typically polished and mold release is applied. Typically, patterns are created for material being used ( it comes in rolls usually 12-50" wide). The material, cut into pattern shapes, is ready for installation to the mold. Depending on the specific process used, depends on how the resin is applied to the part. For wet layups, the mold can be coated in resin, then the material applied, then more resin applied, then more plies (as required). Usually, a vacuum bag is applied to the outside of the part to remove the air trapped in the resin - it makes a stronger part. The part is then set to cure (heat can be used to accelerate). Once cured, the bag is removed then part removed from the mold.

That is the quick answer to how it is done. THere are many good books on the subject, and I have seen some recently which are geared towards automotive applications (check motorbooks international).

As an interesting sidenote, I toured the Roush shops about 8 years ago, and noted that his race bodies were all "wet layup" carbon fiber and kevlar. You can get good quality parts this way, but it does take practice, and even the best can screw up parts. Also, the finish quality is not necessarily the best, as the original viper cowls were a form of wet lay-up carbon, and Dodge went away from this process for quality and rate reasons (the hoods took longer to make than the car!).


2004/5 Saffron Yellow Elise (on order):)
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