How Is Carbon Fiber Made?

Carbon fiber manufacturing is no easy process. There are many detailed steps to create this quality, lightweight yet hard-as-steel material. If you’re interested in crafting a new carbon fiber design for your carbon fiber prototype, here’s what you need to know about the creation of this composite material.

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.

Making Carbon Fiber Starts with a Precursor

No matter the industry or use case, a precursor must be used to craft carbon fiber composite material. This is the raw material that is used to create carbon fiber. For example, the first high-performance carbon fiber materials were made from a rayon precursor.

Nowadays, around 90% of the carbon fiber materials crafted are made from polyacrylonitrile while the other 10% or so are made from rayon or petroleum pitch as a raw material. These are all classified as organic polymers because their molecular structures are long.

Manufacturing Carbon Fiber Material

The carbon fiber manufacturing process begins with carbonization. To manufacture carbon fiber, the precursor needs to consist primarily of carbon atoms. This means that any other atoms within the structure need to be expelled before the carbon fiber is made.

First, the precursor is pulled into long fibers, which are then heated at incredibly high temperatures. These fibers are heated without the presence of oxygen to ensure the material doesn’t burn. This causes vibrations in the precursor that dispel any non-carbon atoms from the material.

Treatment

Following carbonization, the surface of the carbon fibers must be treated to bond with epoxies or other binding agents. What oxygen was missing from carbonization is often used here: by oxidizing the surface of the new carbon fiber, it increases the ability for chemical bonding while simultaneously roughening the surface for better physical bonding. This makes it usable for structural carbon fiber projects.

Oxidation can be utilized in a number of different ways. The carbon fiber can be exposed to carbon dioxide, ozone, or even nitric acid, though immersing the product in air yields the desired result.

Sizing

Before you’re able to craft your carbon fiber prototype, the carbon fibers must be sized, meaning they are coated to protect them during the weaving process. They are usually coated in an adhesive like epoxy or nylon. Then they are wound into bobbins, spun, and made into yarn to build a prototype.

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% density and are approximately 1.7 times stronger and stiffer than aluminum at 56%, 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
• High-temperature tolerance

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 composite 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 are manufactured with this method largely depends on the desired product’s properties and use.

Wet Layup, Vacuum Bagging, and Resin Transfer

In these processes, wetted with epoxy, carbon fiber cloth and/or unidirectional material is placed on a tool shaped like the desired part. The excess resin is mechanically removed with a wet layup, 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.

Now that you know the trade secrets of how carbon fiber is made, you have a better idea of what goes into crafting your carbon fiber design. Carbon fiber manufacturing is constantly evolving, so be sure to keep up with your research to know which additional lightweight materials are developed!