The Investigation of Overflow Water-Powered Projectile-Assisted Injection Molded Short-Glass-Fiber-Reinforced Polypropylene

Water-powered projectile-assisted injection molding (W-PAIM) is a novel injection molding technology that has been recently developed based on the ripe water-assisted injection molding (WAIM). Fiber orientation pattern and residual wall thickness (RWT) are two crucial factors determining the quality of W-PAIM parts composed of short fiber-reinforced thermoplastics (SFRTCs). However, limited work has been conducted on W-PAIM of SFRTC parts, which restricts its application process. In this work, an intensive investigation of W-PAIM parts composed of short fiber-reinforced polypropylene was conducted via a newly lab-developed W-PAIM platform. The results indicated that fibers were quite well oriented in the region extending from the core zone to the water channel, especially in the water channel zone, but randomly aligned in a small region near the mold wall. Nevertheless, fibers in the water channel zone of W-PAIM part were highly oriented, presenting an opposite alignment trend in fiber orientation compared to that in the water channel zone of the WAIM part as reported earlier. These disparities in fiber orientation between W-PAIM and WAIM parts were primarily attributed to the strong flow fields generated by projectile penetration. Additionally, the influence of three main processing parameters that significantly affected the projectile penetration on these two crucial factors was also investigated using the single-factor method. It was discovered that water injection delay time constituted the primary factor affecting the projectile penetration process, and reducing this time could greatly increase the relative thickness of the ordered area and the uniformity of RWT. More importantly, within the value range of the tested processing parameters, increased water pressure, elevated melt temperatures, and shorter water injection delay time could simultaneously improve fiber orientation and the uniformity of RWT in W-PAIM parts, which may improve the properties of W-PAIM parts and enlarge their application scope. This work provides a comprehensive guide for the fabrication of W-PAIM parts of SFRTCs.