Abstract
Injection molding process has been extensively applied to the production of plastic parts. In the recent years, the improvements both in the numerical methods and computer hardware have promoted the application of CAE in the modeling of the injection molding process. The major drawbacks of the Hele-Shaw approximation, commonly used today as a means of simplifying the simulation of injection molding process, are the inherent loss of the ability to predict the important physical three-dimensional phenomena, and the ambiguity involved in the definition of a mid-plane. This work presents an implicit finite volume approach to simulate the three-dimensional mold filling problems encountered during the injection molding. The described numerical model deals with the three-dimensional non-isothermal flow of incompressible, non-Newtonian fluids with moving interfaces. The collocated finite volume method and the SIMPLE segregated algorithm are used to discretize and solve the flow governing equations. All vector or tensor variables are computed in their Cartesian components, and hence no coordinate transformation is required, which considerably simplifies the complicated fully three-dimensional primitive variables flow calculation. In addition, a bounded compressive high-resolution differencing scheme is adopted to solve the advection equation to capture the interface on a Eulerian framework. This approach effectively solves the flow field in terms of CPU time and memory storage as well as the complicated three-dimensional melt front topology. Extensive calculations were performed for several two- and three-dimensional examples to assess the accuracy, efficiency and robustness of the proposed numerical model. To validate the proposed methodology, several typical examples of free-surface testing problems were analyzed. Moreover, the accuracy of the present three-dimensional model is further confirmed through the comparison with the Hele-Shaw model in the simulation of mold filling of several thin mold cavities. Examples of the filling simulations of traditional injection molding, gas-assisted injection molding and IC plastic encapsulation were presented to illustrate the capabilities of the current numerical method. The analysis results of traditional injection molding indicate that the present approach can accurately predict the critical three-dimensional flow phenomena i.e., fountain effect, side wall effect and lateral flows in thickness-change regions. Moreover, for the simulation of real industrial cases of complex geometries, the prediction results are in good agreement with experimental data. In the simulation of gas-assisted injection molding, the three-dimensional model can predict both the polymer and gas injection phases. Moreover, the critical gas penetration behaviors such as penetration length, blow-through, corner effect, fingering effect and gravity effect can also be simulated. Finally, a fully three-dimensional analysis without model simplifications was performed to simulate the plastic encapsulation of a TSOP II of highly-complicated leadframe layout. In this case, the chemorheology of EMC is also included to consider simultaneously the effects of degree-of-cure, temperature and shear-rate on the viscosity of EMC during encapsulation. The analysis results presented in this work indicates that the proposed methodology is a powerful fully three-dimensional analysis tool not only for injection molding but also for the other engineering applications with free-surface flow.