Using a Visualization Mold to Discuss the Influence of Gas Counter Pressure and Mold Temperature on the Fountain Flow Effect

Abstract

Abstract The fountain flow effect in a mold cavity results in molecular orientation that is likely to create flow-induced residual stresses, warpage of finished products, and excessive shrinkage, thus making it difficult to guarantee high precision control. This study uses a gas counter pressure technique to inhibit fountain flow and employs a visualization mold design to observe the influence of counter pressure on melt flow behavior, in order to discuss the impact of the counter pressure mechanism on the fountain flow. The visualization mold designed herein and the clip cavity help to test the counter pressure mechanism in injection molding, while the observed particles and high-speed camera assist in observing the influence of fluid flow behavior and counter pressure on the fountain flow effect. The study observes and tracks the flow trajectory of particles in the melt, with findings showing that the closer the flow line of the melt is to the mold wall, the shorter the offset distance will be to the outward flip. Moreover, the closer to the center, the longer the offset distance of the outward flip meaning that it flips outwards in the melt-front nearby the center line and stays on the mold wall surface to form a new frozen layer. The melt-front length changes under different counter pressures and different mold temperatures. The front length changes present the inhibitory effect of counter pressure on the fountain flow, which is more apparent at the far gate than at the near gate. The melt-front lengths of the counter pressure of 0 bar at mold temperatures of 40 °C and 20 °C increase 1.5% and 4.7%, respectively, meaning that the thicker the frozen layer, the more apparent the fountain effect.