DefinePK

Abstract

Micro metal injection moulding (µMIM) can be perceived as one of the key technologies for mass micro manufacturing due to its large scale production capability. In micrometer regime, surface roughness is important in view of the microstructure tolerances and in an application where exposure to friction and wear is necessary. Furthermore, reduction of shrinkage affecting the shape stability in the form of induced warpage is also critical. The use of recyclable-based plastics as binder such as polyethylene, polystyrene, polypropylene and etc. can create a green micro parts manufacturing by recovering waste plastic. Plastic recycling promotes reduction of greenhouse gas emissions and saving the landfill area. For production cost benefits in µMIM otherwise, the mould design should has the capability to fully or semi operated for each injection cycle and the mould should also relatively low in cost. This study focuses on fabricating low cost micro moulds with and without ejector system to cope with the aforementioned issues. The binder system used was polyethylene, mixed with stainless steel powder to form the feedstock. Mould inserts were machined from mild steel block by CNC milling machine and cavity was precisely cut out from mild steel plate through electrical discharge wire cutting (EDM-Wire Cut). The EDM-Wire Cut has the capability to cut the conductive materials with close tolerance and relatively cheaper than other method. The part was in dog bone shape with diameter of 2.84mm and the overall specimen length was 9mm. Horizontal plastic injection moulding machine was occupied to inject the feedstock into the mould cavity. Performance of the fabricated low cost moulds were tested and benchmarked by the part shrinkage and surface roughness value (Ra). Results reveal that the obtained shrinkage was within 14 – 19%, produced from both moulds with and without ejector system. The superior surface finish was obtained in average at 0.5µm from part that injected through the mould without the ejector system.