Primary and secondary gas penetration during gas-assisted injection molding. Part I: Formulation and modeling

A theoretical study has been carried out on the transient gas-liquid interface development and gas penetration behavior during the cavity filling and gas packing stage in the gas-assisted injection molding (GAIM) of a tube cavity. A mathematical formulation describing the evolution of the gas/melt interface and the distribution of the residual wall thickness of skin melt along with the advancement of gas/melt front is presented. The physical model is put forward on the basis of Hele-Shaw approximation and interface kinematics and dynamics. Numerical simulation is implemented on a fixed mesh covering the entire cavity. The model and simulation can deal with both primary and secondary gas penetrations. The predicted and measuredresults are compared in Part II of this study to validate the theoretical model