Investigation of the inflow effect on weld lines morphology and strength in injection molding of short glass fiber reinforced polypropylene

In parts manufactured by injection molding, the regions affected by the presence of a weld line show worse mechanical properties, especially in the case of fiber-reinforced thermoplastics. This is mainly due to the unfavorable reinforcement orientation in the proximity of the weld line. The position and shape of a weld line, which develops where two different flows converge during the mold filling phase, can be modified by generating a pressure unbalance between flow fronts during the packing phase. This phenomenon is also known as "inflow" in the literature. In this work, the inflow phenomenon was obtained using side features located near the weld line. Its effect on weld line morphology and fibers orientation was investigated. The experimental results show that the inflow can modify the weld line position and shape. Furthermore, it can reorient the fibers in the weld line region, increasing the load at break and stiffness of the weld line by 19% and 15%, respectively. These effects were numerically modeled with a maximum error of 4%.