Targeted Manipulation of Fibre Orientation Through Relative Movement in an Injection Mould

Abstract

The injection moulding of fibre-reinforced plastics leads to a flow related characteristic microstructure with fibres aligned in flow direction in the shell layers and fibres aligned transversely to the flow direction in the core layer. The combination of a design related gate location and the flow related microstructure can lead to an unfavourable fibre orientation. For example, the flow direction for rotationally symmetric parts under internal pressure is often in axial direction and therefore the main fibre orientation is transversely aligned to the critical tangential tension. This leads to high wall thicknesses, increase in weight and material inefficiency. This paper shows first results of the targeted manipulation of the fibre orientation for long and short fibre reinforced thermoplastics through relative movement. The relative movement of opposing mould surfaces is realised through a rotating core in the injection mould and allows the reorientation of the fibres in tangential direction through shearing of the melt. The evaluation of this process is done by mechanical tests, microscopic investigations and computed tomography scans and shows a significant increase of transversely aligned fibres.