The influence of PMMA content on the properties of 316L stainless steel MIM compact

The influence of the PMMA content in a composite binder comprising PMMA and PEG on the moulding, debinding and sintering behaviour of injection moulded samples of 316L stainless steel powder has been investigated. The PEGs component of the binder is readily soluble in water, so that, after leaching, a network of open pores is provided to facilitate the extraction of the PMMA by pyrolysis. This has been shown to lead to a reduction in overall debinding time. It is shown in the present study that reduction in the PMMA content allows injection moulding to be carried out at a lower temperature, while having the unfavourable consequences of reducing the stiffness and the green and brown strengths of the mouldings. It was also found that the mouldings had to be left in the die for a longer period before ejection because the temperature at which the binder stiffens was significantly reduced. It was shown that reducing the PMMA content of the binder enhanced the rate of removal of the PEGs during the leaching. The sintered densities of the mouldings were found to increase as the PMMA content increased as, consequently, did the hardness.