Experimental and numerical investigations on formation mechanisms of hollow structures in overflow water‐assisted injection‐molded parts of short‐glass‐fiber‐reinforced polypropylene

Abstract

AbstractIn water‐assisted injection molding processes, it is crucial to understand the mechanisms governing the formation of hollow structures and identify the key factors influencing their morphology and dimensional accuracy. This work combined experimental analysis and numerical simulation to investigate the influence of different mold cavities and main processing parameters on hollow structures in overflow water‐assisted injection molded parts of short‐glass‐fiber‐reinforced polypropylene, that is, hollow shape and hollow ratio. The results show that the hollow shape and hollow ratio depended not only on the cross‐sectional location but also on the cross‐sectional shape of the mold cavity. For the circular parts, the hollow shape resembled the cross‐sectional shape of the mold cavity, with a relatively small and uniform hollow ratio across cross‐sectional locations. For the noncircular parts, the hollow shape varied considerably with increasing distance from the water inlet. Moreover, the results also show that except for the influence of water‐injection delay time on the uniformity of the hollow ratio, higher melt temperature (250°C), shorter water‐injection delay time (0 s), and higher water pressure (10 MPa) contributed to the hollow shape being closer to the cross‐sectional shape of mold cavities and made hollow ratios relatively larger and more uniform.