Sandwich injection moulding with thermoset materials
This project aimed to study the feasibility of making a thermoset sandwich injection moulding from a novel thermoset co-injection moulding system. Two thermoset polyesters, BMC and a powder coating, were used for all experiments. Flow and cure of those materials in a newly designed manifold system were studied and some thermoset sandwich injection mouldings have been produced. Despite producing novel co-injection mouldings using two thermoset materials together, the results showed that the existing system was not applicable for large-scale production of sandwich parts and needed some improvements. The experiments on the moulding materials and single injection of each material gave temperature windows and settings for the co-injection moulding. The results from all experiments indicated that temperature and the time of applying heat to a thermoset material were very important to its flow ability and formation. Especially when producing a sandwich moulding, adequate heat and time was necessary for the skin material to form a sufficient layer to cover the core material. Investigation of the sandwich moulding cross-sections showed that applying more core injection delay time could help to increase the skin thickness. Surface assessmenitn dicated that the surface quality was also improved when the skin layer was thicker. However, core break-through at the position opposite to the mould gate was found in all sandwich mouldings showing that the type of mould gate was also important. A central sprue gated mould used in these experiments was found to be not suitable for producing a sandwich component using this machine configuration. A new manifold design was proposed and was compared to the existing manifold designed by using a simulation software package from Moldflow. Thermoset single injection moulding simulation was used to help to understand the flow and cure of a thermoset material in both manifold designs. It was shown that the new manifold system design was an improvement on the existing one.