Analysis of demolding in micro metal injection molding

In this paper micro metal injection molding (μMIM) is being studied to produce 316L stainless steel microstructures. Experimental work showed that demolding failure was a serious hindrance to the success of μMIM as a suitable technology to produce small microstructures. Thus, a theoretical analysis of microstructure demolding in μMIM is needed in order to understand the demolding behavior theoretically and how to avoid demolding failure in μMIM. In this paper, theoretical analysis of the demolding of 24×24 (totally 576) microstructures was conducted with the help of Abaqus finite element analysis software. The analysis was involved in two factors that possibly lead to demolding failure: one is the shear stress during ejection of the microstructure due to contact pressure between the microstructure and the microcavity, the other is thermally-induced stress due to cooling of the microstructure. The analysis shows that the following factors have significant influence on the demolding: aspect ratios of the microstructure, the coefficient of friction between the microstructure and the microcavity, demolding temperature and holding pressure. And the microstructure that is farther away from the centerline of the round part with microstructures undergoes higher stress and more easily subject to breakage. The moment when the microstructure is the most possibly subject to breakage during demolding is always the onset of ejection.