Vacuum-assisted resin injection moulding

A widely used method of laminate construction is by the contact moulding process or hand lay-up . In this, a layer of catalysed unreinforced resin, known as the gelcoat , is brushed or sprayed onto the mould and allowed to cure and then layers of reinforcing-fibre impregnated with resin are built up behind (Fig. 6.3). Variations of this include resin injection and vacuum-assisted resin injection in closed moulds. After removal of the cured moulding from the mould, the gelcoat forms the outer skin and as such performs the two functions of decoration and protection ... 

Lotus, producers of composite cars since 1957, took a big step forward in 1974 with its new Elite (see Fig. 5.2). This was manufactured by the new VARI process (Vacuum Assisted Resin Injection), in which the two halves of the body are moulded in matched tools, and subsequently bonded together (see Fig. 5.3). The only chassis is a backbone top-hat section in steel otherwise the stability of the body is ensured by integral foam beams (see Fig. 5.4). These foam beams are used to locate and support uni-directional glass rovings, before the polyester resin is injected. The result is an extremely strong body, of which the present Esprit is the latest example. The Lotus system is extremely effective, but no claims are made that it will ever meet the cost and production needs of the mass market. The De Lorean... 

Another type of product is a preform in which the fibres, whether in the form of a mat, fabric or some other construction, are initially formed to a, possibly, complex shape and stabilized with a binder. The preform is placed in a mould and a thermosetting resin injected, sometimes with vacuum assistance, to produce a component (section 11.3). The advantage of this approach is the ability to maintain the fibres in position during a complex moulding operation, increased product quality and improved productivity. 

A variant of low-pressure moulding is catalysed resin injection into matched moulds in which the reinforcement has been preplaced prior to mould closure vacuum applied before resin injection assists mould filling. All these techniques depend on the easy flow of the prepolymer and good wetting of the reinforcement, but preclude the addition of much cheap particulate filler. 

The liquid resin is then injected into the mould, typically from the bottom mould, assisted by pressure and vacuum to aid in providing an even resin distribution and achieving the removal of voids. A key processing consideration here is that the resin flow should match the wetting out and impregnation of the reinforcement. 

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