11 - Compression moulding

Abstract

Compression moulding is a well-established technique for processing polymer composite materials, using either thermoset or thermoplastic matrices. It is sometimes referred to as matched-die moulding, where the fibre-reinforced composite material is forced to deform or flow within the mould cavity. Compression moulding is commonly associated with the forming of composite materials with discontinuous fibre reinforcements, at low (15%) to medium (50%) volume fractions. Compression moulding is used to process pre-impregnated intermediate products to produce semi-structural and structural composite components, for example, thermoset sheet moulding compounds (SMCs), glass mat thermoplastics (GMTs), or long fibre thermoplastics (LFTs). Most recently, compression moulding has been used to process platelet-like materials, i.e. fibre strands or bundles pre-impregnated with a thermoset or a thermoplastic matrix, which are similar in nature to waste thermoset prepregs or recycled thermoplastic materials. This process is attractive because it is easily automated and can be used to produce very complex geometries without any waste, where the shape of the component can be used to enhance significantly the stiffness of the structure (e.g. ribs). Moulding cycle times are typically dependent on part thickness, but range from 60 to 300s, offering one of the fastest moulding processes for thermoset materials. The aim of this chapter is to give an overview of the various moulding compounds and their associated compression moulding processes, and to discuss the effect of processing conditions on the induced microstructure.