how carbon fiber composites are made

How are Carbon Fiber Composites Made?

Carbon fiber composites are made from carbon fiber, epoxy or other resin, and sometimes, metal. How they are made is largely contingent on the desired properties and intended use. They can be manufactured as unidirectional, bidirectional, or quasi-isotropic, and in different shapes and sizes depending on the need. Manufacturing processes for carbon fiber composites include filament winding, pultrusion, matched tooling, resin transfer, and autoclave processing.

In this blog post, we will define what carbon fiber composites are and briefly walk through how they are made.

What are Carbon Fiber Composites?

Carbon fiber is essentially a stranded material, typically compromising thousands of individual graphite fibers. It is a lightweight and extremely durable material. Carbon fiber composites have approx 60% the strength and stiffness of steel at 20% the density and approx 1.7 times the strength and stiffness of aluminum at 56% the density, making it an excellent manufacturing material for many components. Engineers and designers will select carbon fiber composites for demanding applications because of their high stiffness and strength to weight and the fact that they allow for tailoring physical properties in specific locations and directions within a part. 

Benefits of Carbon Fiber

Carbon fiber composites offer a variety of benefits. One benefit is that they can be more durable than other materials. A few other benefits of carbon fiber include:

  • High tensile strength to weight
  • High stiffness to weight
  • Low thermal expansion
  • High chemical resistance
  • X-ray translucency

How Carbon Fiber is Made

Carbon fiber is a composite material that is formed by a combination of chemical and mechanical processes. The process begins with the drawing of long fibers which are then heated to a very high temperature without allowing contact with oxygen to prevent them from burning. This causes carbonization to occur, driving off most of the non-carbon atoms.

The fibers are then heated to high temperatures in various proprietary atmospheres causing chemical reactions between molecules and turning them into carbides that reinforce the fiber conductivity and make it stronger. Details of the process vary depending on the product’s desired properties and use. Once this process is completed,  the fibers can be used in a variety of products from sporting goods to equipment and automotive parts. 

Carbon Fiber Composite Manufacturing Processes

There are multiple different manufacturing processes for carbon composites including; filament winding, pultrusion, wet layup, vacuum bagging, resin transfer, and matched tooling The process chosen will depend on the application.

Filament Winding

In filament winding, carbon fibers are wound around a rotating mandrel. This process is great for making structural components with smooth curved surfaces like racecar bodies and kayaks. It also allows engineers to easily control where the reinforcement is placed in the finished product. Because of this, the details of carbon fiber composites filament winding are dependent on the desired product.

Pultrusion Processes

The pultrusion process creates carbon fiber composites by pulling a resin-impregnated roving through a bath of heated resin to create specific sizes and shapes. How carbon fiber composites manufactured with this method are made is largely contingent on the desired product’s properties and use.

Wet Layup, Vacuum Bagging, and resin transfer

In these processes, carbon fiber cloth and/or unidirectional material, wetted with epoxy, is placed on a tool shaped like the desired part.  With wet layup, the excess resin is mechanically removed, typically with a flexible scraper or squeegee. With vacuum bagging, a bag, or film is positioned over the part and excess resin is removed by vacuum. With resin transfer, the resin is transferred by vacuum into the part after the carbon fiber cloth and bag are assembled on the tool.

Conclusion

Carbon fiber composites are an excellent manufacturing material for many components because of their ability to provide different physical properties depending on where the carbon fibers are placed in finished products. How each component is manufactured will depend upon how much rigidity or reinforcement it needs and ultimately, this process comes down to the desired product’s use.