Flow and heat transfer in compression mold filling

The interaction between heat transfer and flow through temperature-dependent viscosity during compression molding of a cold charge in a hot mold is studied by numerical simulation of two-dimensional cases. The finite-element method is used to solve the equations of motion and energy with a mesh which conforms at every instant to the shape of the charge. The results show that under typical operating conditions a thin layer of warm, low viscosity fluid at the mold surface lubricates the remainder of the charge, which undergoes nearly a planar elongational deformation. For material properties and operating conditions typical of the compression molding of sheet molding compound, very little preferential flow of the material near the mold surface is predicted. The results support the assumption of a flat velocity profile in nonisothermal compression molding used by several workers, and explain the success of some isothermal mold-filling models at predicting mold-filling patterns for nonisothermal cases.