Abstract
In the present study, the simulation of the three-dimensional (3D) non-isothermal, non-Newtonian fluid flow of polymer melts is investigated. In particular, the filling stage of thermoplastic injection molding is numerically studied with a solver implemented in the open-source computational library O p e n F O A M ® . The numerical method is based on a compressible two-phase flow model, developed following a cell-centered unstructured finite volume discretization scheme, combined with a volume-of-fluid (VOF) technique for the interface capturing. Additionally, the Cross-WLF (Williams–Landel–Ferry) model is used to characterize the rheological behavior of the polymer melts, and the modified Tait equation is used as the equation of state. To verify the numerical implementation, the code predictions are first compared with analytical solutions, for a Newtonian fluid flowing through a cylindrical channel. Subsequently, the melt filling process of a non-Newtonian fluid (Cross-WLF) in a rectangular cavity with a cylindrical insert and in a tensile test specimen are studied. The predicted melt flow front interface and fields (pressure, velocity, and temperature) contours are found to be in good agreement with the reference solutions, obtained with the proprietary software M o l d e x 3 D ® . Additionally, the computational effort, measured by the elapsed wall-time of the simulations, is analyzed for both the open-source and proprietary software, and both are found to be similar for the same level of accuracy, when the parallelization capabilities of O p e n F O A M ® are employed.
Highlights
The ever-growing demand for plastic materials promoted an increase in the requirements of many transformation processes, as happens for injection molding (IM), which is currently the most used one to manufacture thermoplastic parts
From all the results presented, we could conclude that both incompressible and compressible formulations were adequate to be used in the simulation of the filling stage of the IM process, with the former being more advantageous in terms of computational cost
A numerical formulation available in the open-source computational library OpenFOAM [2], the openInjMoldSim solver, was assessed in different test cases related to the simulation of the filling stage of the injection molding process
Summary
The ever-growing demand for plastic materials promoted an increase in the requirements of many transformation processes, as happens for injection molding (IM), which is currently the most used one to manufacture thermoplastic parts. For the numerical modeling of IM, Araújo et al [5] provided a parallel 3D unstructured non-isothermal flow solver, with both polymer and air being considered as incompressible fluids Their results presented a good accuracy and reasonable parallel efficiency and scalability. Bird–Carreau rheological model in the interFoam solver available in the OpenFOAM [2] CFD library She studied the filling stage of the IM process and implemented a boundary condition, which allowed the air to escape from the cavity, but not the polymer, as happens in real-life molds. This work describes the numerical validation of an open-source solver, openInjMoldSim [8,9], able to simulate the filling stage of the thermoplastic IM process.
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