Powder Injection Moulding of Metal and Recycled Tyre Rubber Process and Material Characteristics

Technological advancements and environmental concern are two fundamental topics that keep reshaping today's society. This revolution has not left untouched the manufacturing sector. Products and goods are manufactured utilizing the latest technologies in order to rise production efficiency, reduce costs, and decrease the environmental impact.

This dissertation presents a novel process chain for powder injection moulding (PIM) utilizing additive manufactured sacrificial moulds. Even though the use of sacrificial moulds give high designing freedom and reduced tools cost, it generates a new set of challenges. Conventional PIM feedstocks cannot be used since they need to be injected at elevated pressure. The use of high pressure will cause mould failure. Thus, it is necessary to create new feedstocks tailored for this process chain.

Moreover, this PhD project investigates a process chain for end-of-life tyre rubber (ELT) recycling, giving a contribution that tackles the critical problem of waste generation. Tyre rubber is vulcanized and does not chemically interact with the thermoplastic matrix, leading to the creation of compounds with poor mechanical properties. It is impelling to improve the properties of these blends to provide an upcycling technique to recycle ELT.
The main objective of this dissertation is to analyse the influence of feedstocks, both metal and rubber powder based, on the properties of the final part. The aim is to tailor feedstock composition, solid loading and powder particle size distribution to achieve parts with improved properties. This was achieved by using compatibilizers, higher solid loading, and finer powders. The influence of powders with bimodal distribution on the quality of the final product was also investigated. Opposite results were achieved by using bimodal powders with metal and rubber feedstocks, respectively.
The dissertation investigates also the challenges of using additive manufacturing (AM) in a PIM process chain. In order to be able to inject the feedstock without damaging the mould, feedstocks with low viscosity were created. However, the use of low viscosity feedstocks results in powder segregation, generating challenges especially when producing parts with complex shapes.
Finally, a life cycle assessment on the production of blends between PP and ELT was carried out. The investigation showed that, when ELT is used in a thermoplastic blend instead of reprocessing the material as fuel for energy recovery purpose, it is possible to decrease the environmental footprint that ELT has on the toxicity impact categories and on global warming.