Influence of spherulites growth on micro-molding

During micro-molding, unexpected flow pattern has been observed. Small balls are created on the flow front and then merged together with other balls. It is attributed to a flow instability taking place in the contracting flow into micro-channels. From a number of molding tests with different polymers, it has been found that the instability is due to crystallization activity in polymer melts. Moreover, from visualization of polymer spherulites, it has become clear that the onset of this instability is related to the ratio of the micro-channel width and the crystal size. In this work, the same micro-pattern is tested both for injection molding and hot stamping. As in the previous works [1, 2], similar balls are found in injection molded micro-structures. However, no balls are observed in hot stamped ones. We presume this is related to the Deborah number of each molding process.