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Flow analysis of the weld line formation during injection mold filling of thermoplastics

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Abstract

To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. The thermo-rheological findings were used to investigate the sources of weld line weakness. In this way critical areas of the interface in regard to the lack of interdiffusion and the inappropriate molecular orientation were found to be placed near the surface of the finished parts. The main source for the weld line weakness seems to be the V-notch that arises due to the poorly bonded region near the surface in combination with the large shrinkage as a result of extremely high molecular orientations induced at the end of the filling. Furthermore, the empirical knowledge was confirmed that weld lines are rather more sensitive to the local flow situation than the global processing conditions. Melt and mold temperatures can be considered to be the most important factors which influence the weld line strength.

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Reference

  • Bird RB, Armstrong RC, Hassager O (1977) Dynamics of polymeric liquids, vol 1. Wiley, New York

  • Coyle DJ, Blake JW, Macosko CW (1987) The kinematics of fountain flow in mold filling. AIChE J 33:1168–1177

    CAS  Google Scholar 

  • Criens RM, Moslé HG (1983) The influence of knit-lines on the tensile properties of injection molded parts. Polym Eng Sci 23:591–598

    Google Scholar 

  • Fellahi S, Meddad A, Fisa B, Favis BD (1995) Weldlines in injection-molded parts: a review. Adv Polym Technol 14(3):169–195

    Article  CAS  Google Scholar 

  • Fluent, Inc. (1998) FIDAP 8 theory manual

  • Hagerman EM (1973) Weld-line fracture in molded parts. Plast Eng 29(10):67–69

    Google Scholar 

  • Haufe A, Kühnert I, Mennig G (1999) Zum Einfluß strömungsinduzierter Fehlerstellen auf das Versagensverhalten in spritzgegossenen Kunststoffbauteilen. Gummi Fasern Kunststoffe 52(5):354–357

    CAS  Google Scholar 

  • Hirt CW, Nichols BD (1981) Volume of fluid (VOF) method for the dynamics of free boundaries. J Comput Phys 39:201–225

    Google Scholar 

  • Kim S-G, Suh NP (1986) Performance prediction of weldline structure in amorphous polymers. Polym Eng Sci 26(17):1200–1206

    CAS  Google Scholar 

  • Liu S-J, Wu J-Y, Chang J-H (2000) An experimental matrix design to optimize the weldline strength in injection molded parts. Polym Eng Sci 40(5):1256–1262

    CAS  Google Scholar 

  • Malguarnera SC, Manisali A (1981) The effects of processing parameters on the tensile properties of weld lines in injection molded thermoplastics. Polym Eng Sci 21(10):586–593

    CAS  Google Scholar 

  • Mavridis H, Hrymak AN, Vlachopolos J (1988) Transient free-surface flows in injection mold filling. AIChE J 34(3):403–410

    CAS  Google Scholar 

  • Nguyen-Chung T, Mennig G (2001) Non-isothermal transient flow and molecular orientation during injection mold filling. Rheol Acta 40(1):67–73

    Article  CAS  Google Scholar 

  • Nguyen-Chung T, Plichta C, Mennig G (1998) Flow disturbance in polymer melt behind an obstacle. Rheol Acta 37(3):299–305

    Article  CAS  Google Scholar 

  • Piccarolo S, Saiu M (1988) Knit-line structure in the injection molding of polystyrene. Plast Rubber Proc Appl 10:11–16

    CAS  Google Scholar 

  • Seldén R (1997) Effect of processing on weld line strength in five thermoplastics. Polym Eng Sci 37(1):205–217

    Google Scholar 

  • Tadmor Z (1974) Molecular orientation in injection molding. J Appl Polym Sci 18:1753–1772

    Article  CAS  Google Scholar 

  • Tomari K, Tonogai S, Harada T, Hamada H, Lee K, Morii T, Maekawa Z (1990) The V-notch at weld lines in polystyrene injection moldings. Polym Eng Sci 30(15):931

    CAS  Google Scholar 

  • Wei KH, Nordberg ME III, Winter HH (1987) Simulation of planar welding flows: part 2. Strain history, stress calculation, and experimental comparison. Polym Eng Sci 27(18):1390–1398

    CAS  Google Scholar 

Download references

Acknowledgement

The author would like to thank the DFG (Deutsche Forschungsgemeinschaft) for the financial support of the investigation.

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Authors and Affiliations

  1. Institut für Allgemeinen Maschinenbau und Kunststofftechnik, Chemnitz University of Technology, 09107, Chemnitz, Germany

    Tham Nguyen-Chung

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  1. Tham Nguyen-Chung
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Correspondence to Tham Nguyen-Chung.

Additional information

In part presented at the 6th European Conference on Rheology, Erlangen, 2002

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Nguyen-Chung, T. Flow analysis of the weld line formation during injection mold filling of thermoplastics. Rheol Acta 43, 240–245 (2004). https://doi.org/10.1007/s00397-003-0339-2

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  • DOI: https://doi.org/10.1007/s00397-003-0339-2

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