CFRP and CFRP Manufacturing Method

Carbon Fibers and CFRP Manufacturing Methods

The primary advantage of CFRP (carbon fiber reinforced plastic) is that it is “lightweight, strong, and non-corrosive.” These advantages are being further leveraged with advanced-level CFRP products in various fields and markets across the globe. And autoclave molding is the hallmark CFRP manufacturing method for producing high-quality dry carbon with superior design freedom.

CFRP Molding Methods

Molding methods for CFRP are numerous and are selected according to the desired application, shape, and production lot.

Autoclave Molding

RTM (Resin Transfer Molding)　

Va-RTM (Vacuum Assisted Resin Transfer Molding)

Press Molding

Hand Lay-up Molding

Filament Winding Molding

Sheet Winding Molding

Pultrusion

3D Printer

At Uchida, we use the fabrication methods shown in red.

Autoclave Molding Workflow

Fabricating the Molds

First, we design and manufacture the molds for shaping and creating the CFRP end-product.  Unlike in press molding, where an upper and lower mold is needed, in autoclave molding, the inner sections are molded by the pressure of the autoclave. Therefore, we only need to manufacture an outer mold. Material selection includes chemical wood, plaster, metal, CFRP molds, and other materials according to the production quantity and product shape.

DMG MORI TVCM Front Runner Vol.46 

Cutting Prepreg Materials

Prepregs are sheets of carbon fibers that are pre-impregnated with resin. These are first cut to size using a cutting plotter machine. Prepregs are raw materials like foods and have an expiry-of-use date. They generally need to be stored frozen at temperatures of minus 18°C or less.

Laminating Process

Next, our technicians place the cut prepregs layer-by-layer onto the mold, forming a laminate stack in accordance with the specified material design. During this process, rigid measures, including clean rooms and strictly sanitized work wear, are put in place to ensure that no foreign substances, not even a single hair, fall into the layup. While the prepregs are fine 0.08-0.7 mm thick sheets, any air trapped between them during the subsequent autoclave molding process can cause defects such as voids or inter-layer delamination. To prevent this, each layer is vacuum pulled to expel any air.

YAOKI Laminate 01

Vacuum-bagging Process

Once the laminating process is complete, specialized sub-materials such as mold release film and breather cloth bagging film are placed over the layup and vacuum-pulled (vacuum-bagged) to finalize the pre-molding preparation. The vacuum-bags are sealed with sealant tape (yellow sections in the image) to prevent tearing or leaking from any sharp or protruding edges.

YAOKI Bagging 01

Autoclave Molding

What is autoclave molding?

Pressure

Put simply, an autoclave is a pressure device. It pressurizes the inside of the chamber and presses the laminated prepreg sheets against the mold to expel any remaining air.

Temperature

In CFRP (carbon fiber reinforced plastics that use a thermosetting resin) molding, heat causes the resin to react and cure (harden). In the case of CFRTP (carbon fiber reinforced plastics that use a thermoplastic resin) molding, the resin will soften with heat and solidify when cooled. *Similar to chocolate.

Vacuuming

During molding, bagged products are generally vacuumed and air is expelled. The history of the molding process is recorded on paper, or with a digital recording device, and submitted to the client for traceability or stored in accordance with our company’s regulations.

Autoclave

Image of overheating and pressurization inside the device

Molding pressures, temperatures, and vacuuming (inert atmosphere) are all programmed to match the product.

Finishing

After autoclave molding is complete, the product is removed from the mold and de-molded. The product is then trimmed at a predetermined position, drilled, glued, and assembled, surface finished, and in some cases coated to finish the product.

Painting

YAOKI After cure 01

Quality Inspection

After fabrication, we conduct a final inspection of the product, including the exterior form, dimensions, and hold measurements, to ensure that it meets client specifications. In the case of structural products, we conduct non-destructive testing using ultrasonic testing (UT) equipment to verify against any voids or defects in the product or joints, guaranteeing product integrity.

Summary

In this article, we discussed autoclave molding, a key method and term that is synonymous with CFRP manufacturing.

Autoclave molding generally requires a molding cycle of 4-5 hours. The greatest feature of this fabrication method is the exceptional freedom of choice and design for mold and end-product materials and forms, allowing us to take full advantage of CFRPs characteristics and performance capacity. The autoclave dimensions (internal diameter × length) determine the production constraints.

From prototype development to high-mix low-volume production, our autoclave equipment is our most indispensable asset for CFRP production. That credit is given to the exceptional characteristic stated above.