Compression mold filling simulation for thick, nonplanar parts
Liang, Erwin Wen-Ti
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Permalink
https://hdl.handle.net/2142/19673
Description
Title
Compression mold filling simulation for thick, nonplanar parts
Author(s)
Liang, Erwin Wen-Ti
Issue Date
1991
Doctoral Committee Chair(s)
Johnson, Robert E.
Department of Study
Mechanical Science and Engineering
Discipline
Mechanical Science
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Applied Mechanics
Engineering, Mechanical
Plastics Technology
Language
eng
Abstract
A finite element simulation, based on Barone and Caulk's model, is developed to study the compression mold filling over three-dimensional curved surfaces. The effects of charge thickness and surface curvature on the pressure and velocity distributions are examined.
In solving the velocity-pressure type equation, an element-based penalty method is implemented into the simulation. This approach shows great accuracy and efficiency as compared with the mixed formulation and a iteration scheme. The full Barone and Caulk model gives accurate predictions of filling patterns for thick charges. In thin charges, a special numerical treatment of the full Barone and Caulk model is developed by adding artificial elongational viscosity. Finite element results show that this model produces better accuracy in velocity as well as velocity gradient compared with the Hele-Shaw formulation, which is used by most molding simulations.
A new technique is developed for tracking the moving flow front, using a fixed finite element mesh which models the part geometry. For each time step, temporary elements and temporary nodes are generated within the filled region of any element intersected by the flow front. This scheme allows a smooth representation of the flow front and the imposition of exact boundary conditions on the flow front. Other advantages of this scheme are flexibility in mesh generation and the local mesh refinement. This simulation accurately predicts the flow patterns and knit line locations. The formation and motion of knit lines can easily be tracked by this scheme.
A three dimensional shell-like mold cavity is mapped from the physical domain to a planar cavity of uniform thickness in a transformed domain. Two-dimensional flow equations are formulated in the curvilinear coordinate system associated with the mid-surface. The mold filling simulation is performed in the transformed space, as metric tensors and Cristoffel symbols for the surface are provided. The solutions can be mapped back onto the three-dimensional physical space, since all the quantities in the two domains has a one-to-one correspondence.
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