Isotropy of mechanical properties and environmental stress crack sensitivity in injection‐ and injection‐compression molding of polystyrene with different mold temperature

Abstract

In addition to conventional injection‐compression molding and injection molding with dynamic process temperature control, a synergistic combination of both processes has recently been applied in dynamic temperature‐controlled injection‐compression molding. The two‐dimensional holding pressure effect in combination with the long maintenance of the flowability of the melt due to high mold temperature enables particularly large flow path to wall thickness ratios. In the most cases, only the optimized molding of microstructures and aspect ratios is considered without including the changed internal structure of such manufactured components. In the course of this investigation, the influence of different process strategies under variation of the mold temperature on production‐related anisotropies in the mechanical properties and stress crack sensitivity of thin‐walled polystyrene components was examined. The determined mechanical properties are significantly below the values given in the data sheet of the material in the adapted process variant of injection‐compression molding with high mold temperature. However, the results also show a clear homogenization of the direction‐ and flow path‐dependent mechanical properties. In contrast, components produced in this way tend to show increased environmental stress crack sensitivity. This could be attributed to significantly reduced orientations as a result of the favorably proceeding orientation relaxation.

Recent progress in flow‐induced polymer crystallization

“…188 In addition, many strategies have been proposed to tune the finer structure and property of materials in injection molding. 39,[189][190][191] Some research results show that the introduction of appropriate fillers and external force fields in the injection molding process can maintain good flowability of melts and improve the toughness and stiffness of polymer materials. 39,[192][193][194] Qu's team developed an industrial volume pulsation injection molding (VPIM) machine based on direct drive volume control, which can obtain high-quality and complex products without the aid of auxiliary equipment.…”

Effect of static mixer on optical properties of plastic injection molded parts

“…Injection‐compression molding, for example, requires specialty molds, which can provide compression action on the part, thus replacing the packing stage in the injection molding cycle. [ 1,6,7 ] In this way, both the injection molding process and mold are modified. Other novel approaches used for plastic optics include rapid heat cycle molding (RHCM), [ 5 ] conformal cooling systems, [ 8 ] micro‐injection molding, [ 1 ] process optimization and/or defect compensation via simulation, [ 9–15 ] multi‐shot molding, [ 10 ] and runner modifications to improve melt homogenization.…”