Experimental Analysis of Flow Front Advancing Phenomena along Cavity Side

Abstract

A phenomenon in which the flow front advances faster at both sides of a cavity than at the center is frequently seen in injection molding using long rectangular cavities. This paper reports on an analysis of this phenomenon using a Three-Dimensional Glass Inserted Mold and Integrated Thermocouple Sensor.The conclusions of this present study are the following.(1) The advance of the flow front at both sides of the cavity becomes more conspicuous with an increase in the injection rate for all types of resin.(2) The resin temperature increases more rapidly at both sides of the cavity than at the center. It was also clarified that temperature peaking near the cavity walls promotes shear heating at the cavity sides.(3) It was confirmed that the flow front advances further along the sides for GPPS than PP under all conditions. This is considered due to the viscosity in the high temperature ranges of the resin.(4) Flow front advance was confirmed to occur even at low injection rates for GPPS, and this is considered to be due to the resin stagnation which occurs at the cavity corners.(5) The change in the amount of flow front advance with changes in cavity thickness was confirmed to be very small with a maximum value of 1mm(6) The above results, in addition to the flow front advancing phenomenon model proposed by Yokoi et al., demonstrate that the following four factors influence the flow front advancing phenomenon at both sides of the cavity; (1) injection rate, (2) resin viscosity, (3) resin stagnation occurring near cavity corners, (4) cooling effects of cavity wall.