Formation mechanism of high‐pressure water penetration induced fiber orientation in overflow water‐assisted injection molded short glass fiber‐reinforced polypropylene

Effects of Processing Method and Parameters on the Wall Thickness of Gas-Projectile-Assisted Injection Molding Pipes

Gas-Projectile-Assisted Injection Molding (G-PAIM) is a new injection molding process derived from the Gas-Assisted Injection Molding (GAIM) process by introducing a projectile to it. In this study, the short-shot method and the overflow method of both the G-PAIM and GAIM processes were experimentally compared and investigated in terms of the wall thickness of the pipes and its uniformity. The results showed that the wall thickness of the G-PAIM molded pipe was thinner and more uniform than that of the GAIM molded pipe, and the wall thickness of the pipe molded by the Gas-Projectile-Assisted Injection Molding Overflow (G-PAIM-O) process was the most uniform. For the G-PAIM-O process, the influence of processing parameters, including melt temperature, gas injection delay time, gas injection pressure, melt injection pressure and mold temperature, on the wall thickness and uniformity of the G-PAIM-O pipes were studied via the single-factor experimental method. It was found that the effects of gas injection delay time and gas injection pressure on the wall thickness of the G-PAIM-O pipes were relatively significant. The wall thickness of the pipes increased with the increase in gas injection delay time and decreased with the increase in gas injection pressure. The melt temperature, melt injection pressure and mold temperature had little effect on the wall thickness of the G-PAIM-O pipes. In general, the wall thickness uniformity of the G-PAIM-O pipes was slightly affected by these processing parameters.

Improved process moldability and part quality of short-glass–fiber-reinforced polypropylene via overflow short-shot water-assisted injection molding

Water-assisted injection molding (WAIM) is a promising molding process developed based on conventional injection molding (CIM). It has been a research hotspot in recent years and is still receiving extensive attention from many scholars and industries because of its significant potential advantages in practical applications. However, compared with CIM, since the additional water-related parameters are involved, the process moldability of thermoplastics is significantly reduced, especially for fiber-reinforced thermoplastics, which stunts the development of WAIM process. In this work, short-shot WAIM with an overflow cavity (OSSWAIM) was developed to address the problems and broaden the application scope of WAIMs. The results showed that compared with overflow WAIM (OWAIM) and short-shot WAIM (SSWAIM), OSSWAIM could significantly improve the process moldability and part quality of fiber-reinforced thermoplastics, especially for thermoplastic composites with a high fiber weight fraction. Besides, it was also found that water penetration had a slight influence on the fiber orientation near the water inlet, but had a significant influence on the fiber orientation near the end of mold cavity. Finally, three processing parameters affecting the water penetration, i.e., water pressure, melt temperature, and water injection delay time were investigated in terms of their influences on the fiber orientation within OSSWAIM.