When to Use Carbon Fiber

Carbon fiber is a great material for the right part. It's also expensive, slow to make well, and unforgiving of a design that wasn't made for it. Some parts are better in aluminum, steel or glass fiber, and it's much cheaper to find that out before any tooling is cut. These are the questions worth answering first.

Is weight the problem?

Carbon earns its cost where grams matter, or where stiffness for the weight is the whole point: moving parts, things people carry, things that go fast. If the part bolts to a machine frame and nobody will ever weigh it, aluminum or steel will be cheaper, quicker to make and easier to fix.

Which way do the loads go?

A laminate is very strong and stiff along its fibers and much weaker across them and through the thickness. It's at its best in bending and tension when the plies are laid up for the load. It's weaker at bolt holes, sharp corners, and anywhere a point load tries to peel the layers apart. A part that's mostly bolted joints, or that takes hits on its edges, needs inserts, local reinforcement and generous radii. Or a different material.

How hot will it get?

The fibers don't mind heat. The resin does. Every epoxy has a glass transition temperature where it starts to soften. A room-temperature-cure epoxy can get there well below 100 °C, while high-temperature systems are rated much higher. Under a hood, near an exhaust, or in a black part sitting in summer sun, check the resin before the design goes any further. Clear epoxy also yellows in sunlight, so outdoor parts need a UV-stable clear coat.

What will it touch?

Carbon conducts electricity and sits far from aluminum on the galvanic scale. Bolt bare carbon to aluminum somewhere wet or salty and the aluminum corrodes. The usual fix is a layer of glass fiber on the contact faces, sealant, and isolated or coated fasteners. Easy to design in. Annoying to retrofit.

How many, and how soon?

Hand layup is fine for a handful of parts and expensive for a thousand. Compression molding and other tooled processes bring the part price down, but the tooling gets paid for first. If the volume is uncertain, pick a route that starts cheap and scales. We wrote up how the tooling usually steps up from the first prototype.

Do you need carbon fiber, or the carbon look?

Sometimes the part only needs to look like carbon fiber and doesn't need its strength. A cosmetic carbon skin over a cheaper structure can be the right call, as long as it's described that way. If it's sold as structural carbon, it should be structural carbon.

Can it be inspected and repaired?

Metal dents where it's hit. Carbon can take an impact, look fine, and be damaged inside. For safety-critical parts, decide early how they'll be inspected and whether a damaged part gets repaired or replaced.

Glass fiber and aluminum aren't failures

Glass fiber costs a fraction of carbon and handles impact better, at the price of more weight and less stiffness. Aluminum is cheap, quick to machine and easy to recycle. A good review sometimes ends with one of those, and that's a fine outcome if it's the right material for the part.

These are the first questions we ask on any carbon fiber project. Send a drawing or a photo and a sentence on what the part has to do.