Abstract: The mixture flow of feedstock in metal injection molding(MIM) includes flow of powder and binder, whose viscous behavior is different from the single-phase flow of polymer binder. The research on viscous behavior of MIM feedstock in the micro mold cavity and the minimum channel size proper for injection process are necessary. At four constant temperatures，the viscous behaviors of 16 m 316L feedstock are tested by using seven capillary dies with diameter between 0.3 mm and 2.0 mm, which shows that the tested viscosities by different sizes of dies are not same even at the same temperature and the same shear rate; the difference of tested viscosity is explained and factors affecting the tested viscosity values are discussed; the boundary slip velocity on the capillary wall is calculated on the basis of a series of tested values; the concept of critical size is proposed and a method is suggested for the decision of minimum channel size injected by the 16 m 316L feedstock. The method is also applicable for injection process with different size of feedstock.

Key words: Slip velocity, 316L feedstock, Critical size, Metal injection molding, Viscous test