Methods Applied in Carbon Fiber Fabrication

Carbon fiber fabrication is a great method for constructing or making weightsensitive components and products because the material has a very competitive low-weight characteristic. Carbon fiber also adds strength to these components and products like carbon fiber business cards. Carbon fiber fabrication is also employed in production of spas, bathtubs, shower stalls, truck cabs and many other common home and industrial-use products.

Carbon fiber fabrication begins with the selection of the fabrication technique. Selection depends upon part design, speed, cost and end-use or application of the item. Below are some of the methods to consider:

  1. Hand layup is the most basic of all fabrication methods. In this method, layers of dry fabrics or carbon fiber sheets are placed on a tool to make a laminate stack. Then resin is applied on the layers through resin infusion process. The alternative is to lay on the tool, a fabric that has been pre-impregnated with resin.

Wet layup process involves compacting the layers by placing plastic sheet materials on top (called vacuum-bagging) or by hand using rollers.

Curing in this method is achieved in a number of ways. The most basic form of curing involves adding a catalyst or hardener additive into the resin and occurs at room temperature. Debulking not only consolidates the layup but also removes air trapped in the resin matrix that would otherwise create undesirable voids (air pockets) in the laminate that could weaken the composite.

Increasing temperature quickens curing. A vacuum, oven and pressure can be used to add heat during the curing process. A vacuum is initiated before curing using a vacuum bag placed on top of the whole layup and attached to the tool. This method is advantageous as it can remove gases that result when the matrix is undergoing through chemical curing processes, thus consolidating and strengthening the materials further.

Pressure curing in fabrication of carbon fiber manufacturing is done by way of an autoclave. Modern systems use computer methods to monitor and control the temperature, vacuum, pressure and inert atmosphere in the autoclave. The autoclave is very expensive and many who own it cure several parts simultaneously. Heat curing involves raising the temperature for some time then lowering it to room temperature. Other methods include Electron-beam (E-beam) curing.

2. Open molding: This is a low cost method of making fiberglass composite products. The technique is used to manufacture a wide range of components, including large, noncomplex shapes such as spas, bathtubs, shower stalls truck cabs. There are two options in this case, namely, hand layup and sprayup.

In hand layup, workers compact laminates by hand using rollers. It is being replaced by high-speed production methods such as hybrid injection. In the sprayup carbon fiber fabrication technique, the mold is treated with a mold release, and then gel coat is sprayed to the mold and the mold is ready for fabrication to start.

3. Hybrid injection molding or thermomolding: In high volume molding, industries use compression molding, injection molding, and hybrid injection molding or thermomolding. In injection molding process, chopped glass fiber is forced through a heated barrel using a ram or screw-type plunger. This method can produce as many as 2,000 small parts per hour.

Hybrid injection molding or thermomolding involves mixing of plastics and composites processes. An example is the SpriForm. This method of carbon fiber fabrication involves using both compression and injection molding in a single 90-second fabrication process. It has been used in automotive industry to make a tailored composite seat back that is 40 to 50 percent lighter than its steel version.

Filament winding is also used to make carbon fiber sheets. It uses a long, cylindrical tool called a mandrel suspended in between two end support and used to place place fiber onto the tool in a predetermined manner. Computer-controlled filament-winding processes are available today.

Other highspeed production methods includes tube rolling method used to produce finite-length tubes and rods. Tube rolling involves cutting the material into very fine pieces, laying them on a flat surface, and then rolling a mandrel over the pieces at high pressure and heat.

Pultrusion involves pulling the reinforcing fiber (usually roving, tow or continuous mat) through a heated resin bath and making the specific shape or carbon fiber sheet as needed.

Other methods are centrifugal casting, automated tape laying (ATL) and automated fiber placement (AFP).

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