Injection Moulding of 316L Stainless Steel Powder Using Novel Binder System

Abstract

Powder injection moulding based on a novel binder system, and using 316L stainless steel powder as a test material, is described. The binder system comprises a major fraction of polyethyleneglycols (PEGs) of various molecular weights and a minor fraction of very finely dispersed polymethylmethacrylate (PMMA) incorporated in the form of an emulsion. The feedstock was mixed as a thick, aqueous slurry at room temperature and was rapidly homogenised by stirring at a low shear force, which should minimise contamination because of a much reduced wear rate of the mixing equipment. The possible demixing during the drying of the slurry was minimised by frequent stirring during this stage and the use of some shear mixing of the dried feedstock. The green strength of the moulded specimens was measured by a three point bend test. In the first stage of debinding, the PEGs were removed by water leaching from the moulded components. This opened up pore channels which allowed much faster removal of the remaining PMMA binder during subsequent thermal debinding. The debinded samples were sintered at different temperatures and the sintered samples were examined by SEM and optical microscopy for pore structure and defects such as cracks