Processes


There are numerous methods for fabricating composite components. Some methods have been borrowed (injection moulding, for example), but many were developed to meet specific design or manufacturing challenges. Selection of a method for a particular part, therefore, will depend on the materials, the part design and end-use or application.

Composite fabrication processes involve some form of moulding, to shape the resin and reinforcement. A mould tool is required to give the unformed resin /fibre combination its shape prior to and during cure.

The most basic fabrication method for thermoset composites is hand layup, which typically consists of laying dry fabric layers, or “plies,” by hand onto a tool to form a laminate stack. Resin is applied to the dry plies after layup is complete (e.g., by means of resin infusion). Process_handlayupIn a variation known as wet layup, each ply is coated with resin and “de-bulked” or compacted after it is placed.

Several curing methods are available. The most basic is simply to allow cure to occur at room temperature. Cure can be accelerated, however, by applying heat, typically with an oven, and pressure, by means of a vacuum. vac bagFor the latter, a vacuum bag, with breather assemblies, is placed over the layup and attached to the tool, then evacuated using a vacuum pump before cure. The vacuum bagging process consolidates the plies of material and significantly reduces voids due to the off-gassing that occurs as the matrix progresses through its chemical curing stages.

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