聚合物注射成型流动残余应力的数值分析

建立了可压缩黏弹性聚合物熔体在薄壁型腔中充模/保压过程中非等温、非稳态流动 的数学模型,用数值方法实现了注射成型过程中流动应力和取向建立及松弛过程的模拟,研 究了熔体温度、模具温度和注射速率等工艺条件对分子冻结取向的影响,取得了与实验相符 的结果.

Numerical analysis of flow-induced residual stresses in injection molding for polymer

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.