Process Encyclopaedia

Composite forming

Overview

Materials and shapes

• Hand lay-up is perhaps the most familiar process. It can be used for components of virtually any size, but usually simple shapes. Similar shapes can be made by spray-up, which is faster but more expensive. Both process can suffer from quality problems - these can be reduced by using vacuum bagging.
• A variant of compression moulding, called resin transfer moulding (RTM), can be used to make complex parts or where greater dimensional accuracy is required.
• Hollow parts can be made by filament winding which can produce parts with optimised mechanical properties.
• Fibres, tapes and mats are produced by processes called pultrusion and continuous laminating; these can also be used to produce prepregs (composite tapes and mats with resin that has not yet cured).

Economics

• There are few composite forming processes, and the decision of which to use is normally determined first by shape and type of fibre (chopped or continuous), and then by volume of production.
• In general, composite forming is more expensive than in other material classes. This is primarily because of the slow production rate due to the curing time of the resins.
• Hand lay-up equipment can cost under £100, but good quality moulds can cost significantly more and have a lead time of several weeks. It is useful for prototyping or where only a few parts are required.
• Spray-up, RTM and filament winding can be automated, so are usually used for mass production.
• The wear on the dies from the fibres is significant in RTM, and they may need to be replaced after every few thousand injections.

Typical products

External links