Three-dimensional numerical simulation for plastic injection-compression molding

Abstract

Compared with conventional injection molding, injection-compression molding can mold optical parts with higher precision and lower flow residual stress. However, the melt flow process in a closed cavity becomes more complex because of the moving cavity boundary during compression and the nonlinear problems caused by non-Newtonian polymer melt. In this study, a 3D simulation method was developed for injection-compression molding. In this method, arbitrary Lagrangian-Eulerian was introduced to model the moving-boundary flow problem in the compression stage. The non-Newtonian characteristics and compressibility of the polymer melt were considered. The melt flow and pressure distribution in the cavity were investigated by using the proposed simulation method and compared with those of injection molding. Results reveal that the fountain flow effect becomes significant when the cavity thickness increases during compression. The back flow also plays an important role in the flow pattern and redistribution of cavity pressure. The discrepancy in pressures at different points along the flow path is complicated rather than monotonically decreased in injection molding.

Key words： injection-compression molding; simulation; injection molding; melt flow; cavity pressure

Acknowledgements

The authors would like to acknowledge the financial support from the National Natural Science Foundation Council of China (Grant Nos. 51635006 and 51675199), the Fundamental Research Funds for the Central Universities (Grant Nos. 2016YXZD059 and 2015ZDTD028), and the Beijing Engineering Research Center of Advanced Structural Transparencies for the Modern Traffic System.

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