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Influence of process parameters and post-molding condition on shrinkage and warpage of injection-molded plastic parts with complex geometry

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Abstract

The quality of injection molded polymer products can be compromised due to the occurrence of residual stresses inherent to the molding process. In order to determine the parameters that influence the dimensional changes and residual stresses of injection molded polypropylene; computer simulations, chemical, thermal and mechanical characterizations were performed. Statistically, we evaluated two conditions of part geometry (with and without rib), three holding pressures (25, 60 and 96 MPa) and three post-molding conditions (without restriction, with restriction followed by water, and with restriction followed by annealing). The specimens molded with ribs and lower holding pressures showed greater warpage, which agreed with the computer simulations. The smooth specimens submitted to annealing followed by air cooling showed lower warpage in relation to the other two post-molding conditions. The thermal analysis presented a lower degree of crystallinity in the samples without post-molding restrictions. The samples submitted to the annealing heat treatment showed an increase in impact strength, and there was no significant variation in the modulus of elasticity for the post-molding conditions evaluated. The ribbed specimens exhibited higher residual stresses than the smooth specimens. Samples with greater warpage had lower residual stresses. All samples showed a tensile-compression-tensile behavior along the hole depth. The results showed that the shrinkage values were not influenced by any of the parameters evaluated. However, on the warpage the factor that exerts the greatest influence is the geometry of the part, followed by the holding pressure; and the post-molding condition presented the least influence among the analyzed factors.

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Acknowledgements

This work was partially supported by the Coordenação Aperfeiçoamento de Pessoal de Nível Superior Brasil (CAPES) Finance Code 001 and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)—Grants 308567/2018 (C.A.F.) and Fundação de Amparo à Pesquisa do 765 Estado do Rio Grande do Sul (FAPERGS). Project 2019/766-18460-4 FAPESP-FAPERGS.

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  1. Programa de Pós-Graduação Em Engenharia E Ciência Dos Materiais (PPGMAT), Universidade de Caxias Do Sul, Rua Francisco Getúlio Vargas, Caxias Do Sul, RS, 1130, 95070-560, Brazil

    Nayrim Brizuela Guerra, Carlos Alejandro Figueroa & Alexandre Fassini Michels

  2. Programa de Pós-Graduação Em Engenharia Mecânica (PPGEM), Universidade de Caxias Do Sul, Rua Francisco Getúlio Vargas, Caxias Do Sul, RS, 1130, 95070-560, Brazil

    Tiago Marcelo Reis, Tiago Scopel, Michele Strey de Lima & Alexandre Fassini Michels

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  1. Nayrim Brizuela Guerra
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Contributions

Nayrim B. Guerra: writing—original draft and editing. Tiago M. Reis: writing—reviewing and editing. Tiago Scopel: methodology, validation and investigation. Michele S. de Lima: writing— reviewing and editing. Carlos A. Figueroa: writing— reviewing and editing. Alexandre F. Michels: conceptualization, supervision, visualization, and writing—reviewing and editing.

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Correspondence to Alexandre Fassini Michels.

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We would like to submit the manuscript entitled “Influence of process parameters and post-molding condition on shrinkage and warpage of injection-molded plastic parts with complex geometry,” for your consideration for publication in International Journal of Advanced Manufacturing Technology. No conflict of interest exits in the submission of this manuscript, and the manuscript is approved by all authors for publication.

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Guerra, N.B., Reis, T.M., Scopel, T. et al. Influence of process parameters and post-molding condition on shrinkage and warpage of injection-molded plastic parts with complex geometry. Int J Adv Manuf Technol 128, 479–490 (2023). https://doi.org/10.1007/s00170-023-11782-7

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