Methods of composite manufacture
Fibre-reinforced polymer composites (FRPs) can be processed in different ways, depending upon the components final intended use, and can also affect the properties of the part.
The method of processing needs to be considered in the early stages and form part of the life-cycle analysis.
This section briefly looks at some of the ways FRPs can be processed, however we recommend that this knowledge is backed up with further education on the topic.
A mould in the shape of the final component is required. The reinforcement (as a woven fabric) is carefully laid into this mould and the matrix (resin) is poured on and spread, usually with the aid of a roller. This is then left to cure.
A gelcoat can be added to the mould before the reinforcement is placed into it depending on what surface finish is required (the top surface is the side which is face down in the mould). A release agent can also be applied to the mould to assist with removing the part after curing.
This process is used for producing hollow tubes. The reinforcement (as strands) are taken through a resin bath, coating them with the matrix. The excess resin is squeezed out by rollers and the reinforcement fibres are then wound onto a mandrel to form the round, hollow shape. The direction the fibres are wound contributes to the performance properties required of the finished part.
Compression moulding is normally used with pre-preg – reinforcement fibres already impregnated with resin. The pre-preg is placed in an open, heated female mould. The male mould is then placed down on to this with the combination of heat and pressure shaping and curing the component. Parts are then allowed to cool before removing from the mould.
Resin Transfer Moulding (RTM)
A male and female mould is required. The reinforcement (as a woven fabric) is placed into the female mould. The male mould is then pressed down upon this and clamped. Resin is injected under pressure from one side of the mould with optional vacuum assistance at the opposite side. This then “wets out” the fibres and is then left to cure. On some occasions the mould is heated to assist the process.
This process can be used as an extension of the wet lay-up technique. The reinforcement (as woven fabric) is placed into a mould, which can be pre-coated with a release agent and/or gel coat. The resin is then rolled on top.
A plastic film is placed over this and is fully sealed at the edges. A vacuum then extracts the air from process helping to consolidate the part. It ensures that the resin is evenly spread.
Pultrusion is a process used for making long, continuous components such as cable trays (for example, those used in the Channel Tunnel). Multiple strands of reinforcement fibres are pulled from reels along a conveyer-belt type process through guides into a heater. During this heating process the strands are coated in resin.
The warm, resin-coated strands are then pulled through a moulding die, forming the final components shape. It is then cut to the desired length with a saw.
*Photo courtesy of Lamplas*