8 Molding Methods for Carbon Fiber/Composite Materials

Carbon fiber is generally used in the form of composite materials by combining with a matrix (such as resin). Carbon fiber composites offer outstanding performance, featuring high specific strength, low density, high specific modulus, ultra-high temperature resistance, excellent fatigue resistance, and superior corrosion resistance. As a key material for lightweight applications, they are widely used in aerospace, wind turbine blades, sports and leisure, pressure vessels, and the automotive industry.

Carbon fiber/composite materials can be processed using various molding (manufacturing) methods depending on the final product's shape and characteristics.

1.Pultrusion Molding,

also known as pultrusion forming, is a continuous molding method in which carbon fibers impregnated with liquid resin are introduced into and pulled through a heated mold for curing. This process is suitable for forming products with specific cross-sectional shapes, such as rods and tubes.

2.Filament Winding Molding

3.RTM (Resin Transfer Molding) Process
This process involves placing a carbon fiber preform (a pre-shaped product or fabric) inside a sealed male/female mold, then injecting liquid resin under pressure to impregnate the fibers, followed by heat curing. When only a female mold is used, and curing occurs under vacuum pressure, the process is called VaRTM (Vacuum-Assisted RTM). RTM is suitable for small to medium-sized products, while VaRTM is ideal for medium to large-sized products.

4.Compression Molding
This method involves layering resin-impregnated prepreg or SMC (Sheet Molding Compound) onto a mold, then applying pressure and heat for curing. Mitsubishi Chemical has developed the PCM (Prepreg Compression Molding) process, which is based on high-cycle and preforming technologies, and it can also be combined with SMC materials for hybrid molding. This method is suitable for mass production.

5.Autoclave (AC) Molding

An autoclave can be simply described as a high-pressure oven. In this process, prepreg layers are stacked onto a forming mold, covered with an expandable vacuum bag to create a vacuum state, and then placed in an autoclave where pressure and heat are applied for curing. This molding method is ideal for producing high-quality, high-performance products, but it has a long production cycle and higher costs.

6.Oven Curing Molding
Similar to autoclave molding, this method involves stacking prepreg layers onto a forming mold, covering them with an expandable vacuum bag to create a vacuum state, and then curing under vacuum pressure in an oven. While its performance is slightly inferior to autoclave molding, it has lower operating costs and is suitable for larger molded products.

7.Winding Molding
This method involves winding prepreg onto a mandrel (core), followed by heat curing and core removal. It is suitable for manufacturing small to medium-sized tubular and roller-shaped products. Mitsubishi Chemical primarily uses this method for producing golf club shafts and industrial rollers.

8.Injection Molding, also known as injection molding, involves heating and melting thermoplastic resin materials such as carbon fiber-reinforced nylon and polycarbonate pellets, then injecting them into the mold cavity (gap) for shaping. While mechanical properties may decrease, this method is suitable for short cycle times and molding of complex shapes.