BOUNDARY-CONDITIONS IN THE MODELING OF INJECTION MOLD-FILLING OF THIN CAVITIES

A governing equation for injection mold-filling of thin cavities with a power-law fluid is derived. The interaction between upstream delivery channel flow and cavity flow results in a continuously changing gate condition as the total viscous dissipation of the delivery channel-cavity assembly is minimized. Depending upon the relative magnitude of pressure drops or viscous dissipation across the channel and the cavity, the boundary conditions which determine the cavity filling process lie between two limiting cases. Experimentally observed melt front locations from isothermal, Newtonian filling of a constant gap rectangular cavity and of a bi-gap rectangular cavity are reported and the validity of the limiting cases is tested.