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Journal of Rheology / Volume 48 / Issue 4

J. Rheol. 48, 765 (2004); http://dx.doi.org/10.1122/1.1753276 (21 pages)

Stability analysis of injection molding flows

Arjen C. B. Bogaerds, Martien A. Hulsen, Gerrit W. M. Peters, and Frank P. T. Baaijens

Materials Technology, Department of Mechanical Engineering, Dutch Polymer Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands

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We numerically investigate the stability problem of the injection molding process. It was indicated by Bulters and Schepens [Bulters and Schepens (2000)] that surface defects of injection molded products may be attributed to a flow instability near the free surface during the filling stage of the mold. We examine the stability of this flow using the extended Pom–Pom constitutive equations. The model allows for controlling the degree of strain hardening of the fluids without affecting the shear behavior considerably. To study the linear stability characteristics of the injection molding process we use a transient finite element algorithm that is able to efficiently handle time dependent viscoelastic flow problems and includes a free surface description to take perturbations of the computational domain into account. It is shown that the fountain flow, which is a model flow for the injection molding process, is subject to a viscoelastic instability. If the various rheologies are compared, we observe that the onset of unstable flow can be delayed by increasing the degree of strain hardening of the fluid (by increasing the number of arms in the Pom–Pom model). The most unstable disturbance which is obtained after exponential growth is a swirling flow near the fountain flow surface which is consistent with the experimental findings. © 2004 The Society of Rheology.

© 2004 The Society of Rheology

KEYWORDS and PACS

Keywords

injection moulding, flow instability, flow simulation, non-Newtonian flow, shear flow, finite element analysis, rheology, work hardening, swirling flow, Stability, Numerical methods, Pom–pom model, Instability, Injection molding

PACS

  • 83.60.Wc

    Flow instabilities

  • 47.11.-j

    Computational methods in fluid dynamics

  • 83.50.Uv

    Material processing (extension, molding, etc.)

  • 83.50.Ax

    Steady shear flows, viscometric flow

PUBLICATION DATA

ISSN

0148-6055 (print)  

Publisher

The Society of Rheology

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ARTICLE DATA

History
Received 15 Jul 03
Revised 09 Mar 04
Digital Object Identifier
http://dx.doi.org/10.1122/1.1753276

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