Multi-scale Computer Simulations of Multi-tubular Components Manufactured by Water-assisted Injection Moulding

Water assisted injection moulding is a recent development in the manufacturing technology associated with injection moulding. Injection moulding involved the high pressure injection of molten plastic in to a preformed metal mould which defines the exterior of the shape of the object. Water assisted injection moulding is a variant with an addition step in which water is injected into the mould after its has been filled with molten plastic. The water jet sweeps out the molten plastic in its path to leave a hollow tube in which the interior of the part is defined by the water jet. This technology is used for preparing tubular components for use in the automotive industry and for domestic appliances. We have been developing the tecluiology to prepare parts with branches in the tubing. We have used fine-element simulations to explore the relationship between the process parameters and the subsequent final part. Of course such simulations only serve to define the exterior and interior of the tubular part. It is clear from the outline of the technology above that the molten plastic is subjected to a complex pressure and temperature variation with time which vary across the pail and its location within the mould. The specification of the part is in most cases is limited to the geometry and the materials which is used in its preparation, in this case polyamide6 with 30% glass fibre. From the development of plastic processes over the last 50 years we have learnt that the properties of plastic part depend critically on the processing pathway and in particular the timescale for the transformation from molten material to the semi-crystalline solid state. We know from the use of small-angle and wide-angle scattering mapping of the structure and morphology of the multi-tubular components that the level of crystallinity and the extent of preferred orientation varies throughout the part and this may lead to warpage and other geometrical changes in the part during its service life. We have set out to explore how we can use the temperature and pressure variation from the finite element modelling to predict the structure and morphology at different regions in the part in order to be able to establish the parameters which yield a geometrically correct part which is also homogenous in its structure and morphology and hence properties. This paper describes the approach we have taken to make progress with this complex matter of simulations on multiple scales and the application of this technique to realistic automotive tubular components.