Molded geometry and viscoelastic behavior of film insert molded parts

Abstract

Virgin injection-molded tensile specimens without any inserted film and four kinds of film insert molded (FIM) tensile specimens were prepared. They were annealed at 80 C to investigate the effect of residual stresses and thermal shrinkage of the inserted film on thermal deformation of tensile specimens. The FIM specimens with the unannealed film were bent after ejection in such a way that the film side was protruded and the warpage was reversed gradually during annealing and the film side was intruded. Warpage of the FIM specimen with the film annealed at 80 C for 20 days was not reversed during annealing. Processing of the FIM specimens have been modeled numerically to predict thermoviscoelastic deformation of the part and to understand the warpage reversal phenomenon (WRP).Nonisothermal three-dimensional flow analysis was carried out for filling, packing, and cooling stages. The flow analysis results were transported to a finite element stress analysis program for prediction of deformation of the FIM part. The WRP was caused by the combined effect of thermal shrinkage of the inserted film and relaxation of residual stresses in the FIM specimen during annealing. It is expected that this study will contribute towards the improvement of the FIM product quality and prevention of large viscoelastic deformation of the molded part.

Residual stresses and thermoviscoelastic deformation of laminated film prepared for film insert molding

“…It is well known that residual stresses are developed in the FIM parts due to nonuniform temperature and pressure distribution during cooling. Residual stress distribution of the film has been predicted by thermal stress analysis considering thermal shrinkage and viscoelastic properties [12–16]. It was assumed in this study that the laminated film is transversely isotropic, and the viscoelastic behavior satisfies the assumption of the thermorheological simplicity.…”

“…It is well known that asymmetric deformation is induced by the difference in thermal expansion coefficient (CTE) and thermal shrinkage between the laminated film and the polymeric resin used in FIM parts [13, 14]. Since the films were produced by biaxial orientation and annealing, they showed anisotropic properties.…”

Influence of Process Temperatures on Blister Creation in Micro Film Insert Molding of a Dual Layer Membrane

“…The warpage of FIM-parts has been the focus of a number of research works including [7], where it was found that the warpage can be reduced by an annealing step after molding when an unannealed thermoplastic film insert was used.…”

“…Further researchers in this area dealt with the morphology of semicrystalline materials used to overmold the film insert [7,8] and the adhesion between film insert and the molded substrate [10].…”

Prediction of Residual Stress Caused by IML Process and Deformation Due to Thermal Impact

“…Patcharaphum (10) 등의 경우 사출성형 해석 프로그 램인 Moldflow 을 이용하여 sandwich 사출성형 공 정과정을 해석하고, 해석결과를 실험과 비교 하였 으며, Kim (11,12) 과 Park (13)…”