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Modeling and simulation of weld line location and properties during injection molding based on viscoelastic constitutive equation

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Abstract

Weld lines are one of the typical quality issues of injection molded parts. They are unavoidable even for moderate complex products. To explore the formation of weld lines in injection molding, a flow model based on viscoelastic constitutive equation is presented in this article to predict and evaluate of weld lines location and properties, in which Rolie-Poly constitutive equation is used to describe the viscoelastic properties of polymer melts and level set method is used to capture melt front. Furthermore, the formation and evolution processes of weld lines are investigated by co-injection molding technique in simulation, since the processes are determined by the flow front and rheological history of the melt streams. Numerical results show that weld lines can be predicted accurately, and the formation and evolution processes of weld line can be shown more clearly by co-injection molding technique. In addition, properties of polymer melt such as velocity, pressure, principal stress difference, and molecular orientation in the weld line regions are investigated and presented.

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Acknowledgments

This work is supported by Science and Technology Research Key Project of the Education Department of Henan Province (Grant No. 20A430023, 20B130002, 20A110031), National Natural Science Found Projects of China (11971075), and Nanhu Scholars Program for Young Scholars of Xinyang Normal University, which are gratefully acknowledged.

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Correspondence to Qingsheng Liu.

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Liu, Q., Liu, Y., Jiang, C. et al. Modeling and simulation of weld line location and properties during injection molding based on viscoelastic constitutive equation. Rheol Acta 59, 109–121 (2020). https://doi.org/10.1007/s00397-019-01182-8

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Keywords

  • Weld lines
  • Viscoelastic
  • Level set
  • Co-injection molding
  • Orientation