Numerical analysis of flow-induced residual stresses in injection molding for polymer
聚合物注射成型流动残余应力的数值分析

To simulate buildup and relaxation of flow-induced stresses and molecular orientation in injection molding process, a mathematical model is derived that describes the unsteady and non-isothermal flow of compressible viscoelastic polymer melts in the thin wall mold cavity on the base of thin film lubrication approximation. The compressible Leonov viscoelastic constitutive equation and Tait state equation are used in the model to describe the effects of compressibility of polymer melt which occur in the post-filling stage. The model is applied to the injection molding process which is treated in terms of a filling, post-filling and cooling stage and is solved using a finite difference method. Stresses calculated with the model are coupled to birefringence by means of the stress-optical rule. Birefrigence is used to characterize the molecular orientation. The final results are given in terms of residual stresses and associated birefringence in the molded part, as influenced by the processing conditions. The result indicates that, for a given polymer, the main factors affecting flow-induced residual stresses and associated birefringence are flow rate and melt temperature, and with the incompressible case flow-induced residual stresses and associated birefringence are increased when the compressibility of the melt is considered. The result are compared with the birfriengence measurement in the literature and reasonable agreement is obtained.