Residual stresses in gas-assisted injection molding

Residual stresses are a major issue in the mechanical and optical behavior of injection-molded parts. In this study we analyze their development in the case of gas-assisted injection molding (GAIM) of amorphous polymers. Flow-induced residual stresses are com- puted within a decoupled approach, in which elastic effects are neglected in the momentum balance, assuming a generalized Newtonian material behavior. In a staggered procedure, the computed viscous flow kinematics are used to calculate normal stresses employing a com- pressible version of the Rolie-Poly model. For the computation of thermally and pressure induced residual stresses a linear thermo-viscoelastic model is used. A 3-D finite element model for gas-assisted injection molding is employed, which is able to capture the kinemat- ics of the flow front, and whose capabilities to predict the thickness of the residual material layer have been validated by Haagh and Van de Vosse (1998). In order to establish a clear comparison, the development of residual stresses is analyzed using standard injection mold- ing and GAIM for a test geometry