Calculations of the flow-induced residual stress development in the injection moulded plate

Abstract

Simulation of the injection moulding process based on the Leonov viscoelastic fluid model has been developed and carried out to study the flow-induced residual stress development in the injection moulded plate during the entire moulding process. An integrated formulation was derived and numerically implemented to solve the nonisothermal, compressible, viscoelastic flow equations. It has been found that flow stresses arise and vary with the shear flow velocity gradient in the filling phase. During the packing stage when the flow velocities of the polymer melt are greatly reduced, the shear stress and the normal stresses also decrease significantly. However, since the polymer melt has been cooled down near the cavity wall, the flow stresses are frozen in place and exhibit little relaxation in the subsequent cooling stage. As a result, the calculated residual shear stress and normal stresses reach maximum values near the cavity wall. This prediction is consistent with the birefringence measurement observed in the laboratory.