Numerical simulation and experimental measurements were carried out to assess the bending behavior of gas-assisted injection-molded parts. Polystyrene plate parts of different thicknesses, designed with various channel geometries, were gas-assisted injection molded. Part flexible strength was measured by a bending test. It was found that part stiffness basically increases linearly with the inertia moment of the plate. Gas channel design, introducing an additional moment of inertia determined by the geometry of the channel section and the hollowed core, resulted in structural reinforcement of the part. An analysis algorithm based on DKT/VRT elements superimposed with beam elements, representing gas channels of various section geometries, was developed to evaluate part bending behavior. An equivalent diameter was assigned to the beam element so that both the original gas channel and the circular beam had the same moment of inertia. The results from this 2.5-dimensional model were also verified with three-dimensional analyses using the ANSYS program. The present simulations show reasonable accuracy upon comparison to bending tests and predictions from ANSYS. This investigation indicates that it is possible to use the same CAE finite-element mesh modeled for process simulation when performing part structure and warpage analyses, resulting in high computational efficiency. (C) 1999 John Wiley & Sons, Inc.
