基于黏弹性的微注射成型流动模拟

应用有限元方法研究了微注射成型中瞬态、可压缩、非牛顿熔体流动的黏弹性对流动前沿及流动平衡的影响。基于Phan-Thien-Tanner模型建立了熔体流动的本构方程,利用Hele-Shaw假设和简化建立了瞬态、可压缩、非牛顿熔体流动的连续性方程、动量方程、能量方程;为了有效地描述微注射成型的尺寸效应,采用了边界滑移和表面张力边界条件。通过分部积分和待定系数法导出了带有边界信息的变分方程和求解应力分量的半解析公式,构造了有限元离散求解及超松驰迭代算法。模拟结果表明:熔体的黏弹性对浇口附近的压力和后续的熔体流动前沿有重要影响;与黏性模型相比,黏弹性模型可以控制模拟压力的快速增长,减少不同型腔之间的充填差异,与短射实验结果也更吻合。

Flow simulation for micro-injection molding based on viscoelastic model

The effects of melt viscoelastic on melt front advancement and flow balance in micro-injection molding is investigated in terms of transient,compressible and non-Newtonian flow using finite element method.The Phan-Thien-Tanner model is used to represent the rheological behavior of viscoelastic flow.The governing equations for melt flow are established based on Hele-Shaw theory.To effectively describe the microscale effects,the slip boundary condition and surface tension are added in the mathematical model for melt flow in micro-injection molding.The new variational equation for pressure including boundary conditions is generalized using integration by parts,and a semi-analytical formula is derived with undermined coefficient method.To improve the computing efficiency,an iterative strategy based on finite element method and successive over relaxation method is constructed for solving melt flow problem.Numerical simulation reveals that the melt viscoelasticity plays an important role in predicting melt pressure at gate and succeeding melt front advancement in cavity.Using viscoelastic model,the rapid increase of simulated pressure can also be controlled,and the filling difference among different cavities can be reduced.The short shot experiments are in fair agreement with the predicted melt front from viscoelastic model.