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Numerical Methods for Compression Mold Filling Simulation

Three computer simulations, based on the generalized Hele-Shaw formulation, are developed for compression mold cavity filling flows. Predictions of the simulation are compared to experimental filling patterns for a number of examples. Two of the simulations are based on the finite element method. The first simulation uses a mesh that covers the entire part, and temporarily distorts the mesh in order to fit the charge geometry at any given time step. This simulation accurately represents the charge geometry and predicts knit line locations, but is difficult to extend to deal with non-planar parts. The second simulation is based on the nodal control volume approach, and can simulate the filling of thin non-planar parts. This technique utilized a fixed finite element mesh to model the part geometry and a scalar nod a 1 fi 11 factor to represent the charge shape as it flows over the mold surface. The nodal fill factors are also used to approximate the zero pressure boundary conditions on the free flow fronts. Third, a simulation based on the boundary element method is developed. The boundary element method is ideally suited for modeling Newtonian, isothermal mold filling for flat parts of otherwise complicated shape, since no internal mesh is required. Other advantages of the boundary element technique are that the logistics of simulations are greatly simplified and that higher order derivatives are calculated more accurately. Comparisons with experiments show that the simulations accurately predict the non-isothermal mold filling behavior of thin charges of non-Newtonian materials such as sheet molding compound. The generalized Hele-Shaw formulation introduces some error when predicting filling patterns of thick and multi-level charges. The simplicity of the governing equations makes the simulations computationally efficient and easy to develop. Finally, a rectangular shaped mold was instrumented to measure pressure distributions in planar extensional flow experiments and investigate pressure losses at the corners. The results show that the pressure field for thin charge agrees with the Hele-Shaw model. Pressure distributions in thick charges qualitatively follow the trend predicted by a recently developed flow model for sheet molding compound [1].

Lesen Sie die deutsche Zusammenfassung auf Kunststoffe.de
Author
 Tim Osswald

Tim Osswald
Polymer Processing Group
University of Illinois

Information

Free keywords: compression molding, mold filling simulation, Hele-Shaw model, control volume approach, boundary elements
Institute / chair: Department of Mechanical and Industrial Engineering University of Illinois
Language: English
Technical consultant for expert services: Prof. Dr. Charles L. Tucker (Betreuer), Prof. Dr. Jonathan Dantzig
Publication year: 1987
Provider: Wissenschaftlicher Arbeitskreis Kunststofftechnik (WAK) / Kunststoffe.de

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