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Manufacturing Technology Insights | Monday, August 28, 2023
High-volume production demands the use of heated tooling, making compression molding a substantial investment. The process involves placing composite materials into a heated mold and applying pressure to create the desired shape.
Fremont, CA: The manufacturing of composites involves various processes that contribute to the creation of durable and versatile materials. Composites are formed by combining different materials, such as fibers and resins, to achieve specific properties. Here, we delve into the processes used in composite machining to shape and construct these advanced materials.
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Wet Lay-Up
In this process, layers of reinforcement and wet resin are applied onto a mold and evenly distributed using a roller until the desired thickness is achieved. The resin is subsequently cured, often with the application of heat, resulting in the final product. This method is commonly used in the marine industry, utilizing polyester resins reinforced with glass fibers. While flexible and cost-effective, this process can be labor-intensive, and emissions from styrene can pose challenges.
Spray-Up
Chopped fiber reinforcement and wet resin are sprayed onto a mold to build up the required thickness. The resin is then cured. Although faster and more cost-efficient than wet lay-up, the mechanical properties of the resulting composite tend to be lower. Spray-up is suitable for larger and relatively simple structures such as boat hulls, storage tanks, and bathtubs.
Compression Molding
High-volume production demands the use of heated tooling, making compression molding a substantial investment. The process involves placing composite materials into a heated mold and applying pressure to create the desired shape. Compression molding is employed to achieve medium to high-volume production efficiently.
Injection Molding
In injection molding, bulk molding compound is heated and injected into a heated mold. The material is held under pressure until it solidifies. This process is particularly effective for producing smaller components quickly. However, tooling costs are relatively high, making it viable for medium to high-volume production.
Resin Transfer Molding (RTM)
Fiber preforms or fabrics are placed in a heated mold, and reactive resin is injected under pressure. Pressure is maintained until the resin cures, and the part can be removed. RTM is favored for its use in complex and heavily loaded parts across various industries. Vacuum Assisted Resin Transfer Molding (VARTM) is a variant of this process, utilizing a vacuum to inject resin under low pressure.
Vacuum Infusion
This process involves using vacuum to impregnate fibrous preforms with low-viscosity resin. The preforms are saturated with resin, minimizing the distance the resin must travel to achieve even distribution. Vacuum infusion suits large components such as boat hulls and wind turbine blades, providing thorough resin impregnation without placing significant loads on the tooling.
Filament Winding
Fiber tows are passed through a resin bath and then wound onto convex mandrels under tension. As the mandrel rotates, fibers are laid down in the desired geometry to reach the required thickness. After curing, the composite is allowed to cool, potentially at elevated temperatures.
Prepreg
Prepreg involves impregnating fibers, fabrics, or mats with resin. Thermosetting prepregs contain resin hardeners and typically require refrigeration due to their limited shelf life. After cutting plies to shape and orientation, the prepreg is brought to room temperature before further processing.
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