Fabrics are laid up as a dry stack of materials. These fabrics are sometimes pre-pressed to the mould shape, and held together by a binder. These 'preforms' are then more easily laid into the mould tool. A second mould tool is then clamped over the first, and resin is injected into the cavity. Vacuum can also be applied to the mould cavity to assist resin in being drawn into the fabrics. This is known as Vacuum Assisted Resin Injection (VARI). Once all the fabric is wet out, the resin inlets are closed, and the laminate is allowed to cure. Both injection and cure can take place at either ambient or elevated temperature.
Resins: Generally epoxy, polyester, vinylester and phenolic, although high temperature resins such as bismaleimides can be used at elevated process temperatures.
Fibres: Any. Stitched materials work well in this process since the gaps allow rapid resin transport. Some specially developed fabrics can assist with resin flow.
Cores: Not honeycombs, since cells would fill with resin, and pressures involved can crush some foams.
i) High fibre volume laminates can be obtained with very low void contents.
ii) Good health and safety, and environmental control due to enclosure of resin.
iii) Possible labour reductions.
iv) Both sides of the component have a moulded surface.
i) Matched tooling is expensive, and heavy in order to withstand pressures.
ii) Generally limited to smaller components.
iii) Unimpregnated areas can occur resulting in very expensive scrap parts.
Small complex aircraft and automotive components, train seats.
Published courtesy of
David Cripps, Gurit