Analysis of layered structure distinguished by fiber orientation in injection molding (1) - effect of thermal expansion coefficient on warpage deformation behavior

摘要

One of the most important issues to guarantee high quality is the ability to predict the warpage deformation behavior of injection molded thermoplastics. This is especially true for the glass fiber (GF) reinforced thermoplastics, where anisotropy in fiber orientation can lead to the increase of warpage deformation. In this study, we observed cross sections and measured the multi-directional thermal expansion coefficients of GF reinforced polyamide 6 (PA 6) samples of varying weight fractions of glass fiber and thicknesses. In photomicrographs of cross sections, the fiber orientation showed a symmetrical structure of three layers, skin/core/skin, which depended on the weight fraction of glass fiber and the thickness of the molding. The thermal expansion coefficient showed an anisotropy that depended on the fiber orientation. In addition, numerical results obtained using a model that considered the fiber orientation distribution at each layer thickness qualitatively agreed with the experimental measurements of warpage deformation.