THE CONTROL OF FIBER ORIENTATION IN CERAMIC AND METAL COMPOSITES BY OPEN-ENDED INJECTION-MOLDING

In conventional injection moulding of short-fibre-reinforced polymer-, ceramic- or metal-matrix composites, fibres tend to align in the flow direction near the surface but to present anisotropic orientation nea r the centre. This diminishes the fibre reinforcing effect and, in mat rices which require sintering, may cause differential sintering and lo ss of shape. lit this paper, a novel moulding technique is used in whi ch the mould contains an opening through which material is expelled du ring filling and solidification. It is feasible in a manufacturing con text where a two-barrel machine is available or in a single-barrel ope ration where recycling of waste is permissible. This method allowed mo uldings to be made at low pressures without shrinkage defects. The fib res were oriented in the flow direction throughout small section mould ings and in large sections, the unoriented centre was reduced in size. Relaxation studies suggest that molecular orientation was also unifor m throughout the section. (C) 1996 Elsevier Science Limited