Development of a cost-effective hybrid strategy for manufacturing plastic injection mould inserts

Abstract

This research project is focused on the cost-effectiveness of combining metal additive manufacturing (AM) technology with well-established conventional mould-making processes to manufacture high-performance injection mould inserts. Evaluations, analyses and development work were undertaken in three separate phases. Phase one involved the development of a novel hybrid additive-subtractive manufacturing strategy and a hybrid-build technique explicitly for fabricating injection mould inserts. This strategy utilises a simple machined substrate blank as the less complex half of the mould insert for an additive process to build the more complex portion, including its conformal cooling channels, directly on top of it. A series of subtractive finishing operations then finish the insert to reach the required surface finish and precision for the entire mould. Through experimental AM-build work and preliminary metallurgical investigation, the hybrid-build concept has proven to be a time-efficient additive process, and the building technique produced a robust powder-to-substrate interfacial fusion bond. Phase two involved the development of two types of hybrid powder-wrought metallic alloys aimed at injection mould insert applications using the hybrid-build technique from phase one. The first study was on aluminium, and the second was on alloy steel. Three hybridaluminium alloys were developed with properties suitable for general engineering applications and low-volume run injection mould inserts. Subsequently, two hybrid-steel alloys were developed, one of which is pre-hardened, and the other is age-hardenable. Both alloys retain excellent tensile strength and high hardness, making them most suitable for high-performance and durable injection mould insert applications. Phase three, the last phase of the research project, involved designing and manufacturing mould inserts for two real-world tooling projects by applying the manufacturing strategy and materials developed in the two previous phases. Mould performance evaluations established that moulds equipped with conformally cooled inserts would reduce cycle time and unit part cost. Evaluations from customised cost models indicated that, although tooling costs were higher with metal AM processes, the extra costs can be quickly offset within a relatively short period in a high-volume production run environment. Overall, metal AM technology could benefit the plastic injection moulding industry and consumers if applied appropriately to each product and production requirement.