Study of processing parameters for MIM feedstock based on composite PEG-PMMA binder

Binders composed of polyethylene glycols (PEGs), polymethylmethacrylate (PM MA) and, in some cases, stearic acid have been used to injection mould 316L stainless steel powder having a median particle size of about 25 mu m. The effects of changing the molecular weights of the PEGs, of changing the pro portions of the PEGs and PMMA in the binders, and of additions of stearic a cid on moulding behaviour and on removal of the PEGs from mouldings by wate r leaching have been investigated. Reducing the PMMA content allows higher solids contents to be moulded and, for a given solids content, lower mouldi ng temperatures to be used and more rapid removal of the PEGs by water leac hing. However, reducing the PMMA content lowers the stiffness and strength of the mouldings. Reducing the average molecular weight of the PEGs acceler ates the leaching. Introduction of stearic acid allows higher solids conten ts to be successfully moulded.