Numerical Simulations of Residual Stresses and Warpage in Injection Molding

The dimension stability and mechanical performance of injection molded products can be improved by predicting and optimizing residual stresses and warpage during processing. Numerical simulations of residual stresses and warpage were undertaken upon the characteristics of injection molding. A linear thermoviscoelastic model was adopted to simulate thermally and pressure induced residual stresses in amorphous polymer parts. The numerical calculation was carried out by the finite difference method in the time and layer discretization in the thickness direction, combined with multiple boundary conditions during different molding stages. A finite element model formed by combining the membrane element and a bending element was employed in the warpage simulation. A modified flat model was proposed based on surface mesh, which avoided the deficiencies of traditional flat models. Simulation results were compared with experimental data for validation of the developed program. It was found that the numerical simulations and corresponding software could be effective in enhancing the quality of products and productivity.