Dynamic visualization of cavity-filling process in fluid-assisted injection molding-gas versus water

Fluid-assisted injection molding technology, including gas-assisted molding and water-assisted molding, has been widely used to manufacture plastic parts in recent years, due to its light weight, relatively low resin cost per part and faster cycle time. This report is devoted to studying the filling phenomena of fluid-assisted injection moldings by using a dynamic visualization technique. Experiments were carried out on an 80-ton injection-molding machine equipped with gas and water injection systems. The material used was semi-crystalline polypropylene. A flow visualization mold was specially designed and made for this study. A high-speed video camera was used to record the mold filling phenomena of rectangular cavities with different channel geometries and layouts: a flat plate, a plate with two zones of different depths, a plate with symmetrical ribs and a plate with fishbone ribs. The interaction between the assisting media and the polymer melt during molding was observed, and insight into the penetration behavior of the fluid was summarized. In addition, comparisons were made between the mold-filling process by gas-assisted injection molding and water-assisted injection molding.