Wilczyński Krzysztof, Narowski Przemysław
Faculty of Production Engineering, Polymer Processing Department, Warsaw University of Technology, 02-524 Warsaw, 85 Narbutta, Poland.
Polymers (Basel). 2019 Apr 8;11(4):639. doi: 10.3390/polym11040639.
Simulation studies were performed on filling imbalance in geometrically balanced injection molds. A special simulation procedure was applied to simulate properly the phenomenon, including inertia effects and 3D tetrahedron meshing as well as meshing of the nozzle. The phenomenon was investigated by simulation using several different runner systems at various thermo-rheological material parameters and process operating conditions. It has been observed that the Cross-WLF parameters, index flow, critical shear stress (relaxation time), and zero viscosity, as well as thermal diffusivity and heat transfer coefficient strongly affect the filling imbalance. The effect is substantially dependent on the runners' layout geometry, as well as on the operating conditions, flow rate, and shear rate. The standard layout geometry and the corrected layout with circled element induce positive imbalance which means that inner cavities fills out faster, and it is opposite for the corrected layouts with one/two overturn elements which cause negative imbalance. Generally, for the standard layout geometry and the corrected layout with circled element, an effect of the zero shear rate viscosity η₀ is positive (imbalance increases with an increase of viscosity), and an effect of the power law index and the relaxation time λ is negative (imbalance decreases with an increase of index and relaxation time λ). An effect of the thermal diffusivity α and heat transfer coefficient is negative while an effect of the shear rate is positive. For the corrected layouts with one/two overturn elements, the results of simulations indicate opposite relationships. A novel optimization approach solving the filling imbalance problem and a novel concept of global modeling of injection molding process are also discussed.
针对几何形状平衡的注塑模具中的填充不平衡问题进行了模拟研究。应用了一种特殊的模拟程序来正确模拟该现象，包括惯性效应、三维四面体网格划分以及喷嘴的网格划分。通过在各种热流变材料参数和工艺操作条件下使用几种不同的流道系统进行模拟，对该现象进行了研究。已观察到，Cross-WLF参数、指数流动、临界剪切应力（松弛时间）和零粘度，以及热扩散率和传热系数对填充不平衡有强烈影响。这种影响在很大程度上取决于流道的布局几何形状，以及操作条件、流速和剪切速率。标准布局几何形状和带有圆形元件的校正布局会导致正不平衡，这意味着内腔填充得更快，而对于带有一个/两个翻转元件的校正布局则相反，会导致负不平衡。一般来说，对于标准布局几何形状和带有圆形元件的校正布局，零剪切速率粘度η₀的影响是正的（不平衡随着粘度的增加而增加），幂律指数和松弛时间λ的影响是负的（不平衡随着指数和松弛时间λ的增加而减小）。热扩散率α和传热系数的影响是负的，而剪切速率的影响是正的。对于带有一个/两个翻转元件的校正布局，模拟结果表明关系相反。还讨论了一种解决填充不平衡问题的新型优化方法以及注塑成型过程全局建模的新概念。
