Significance of curvature for balancing polymer melt channels in injection molding manifold systems and extrusion dies

Natural rheologic balancing is being state-of-the-art in developing polymer melt channels for extrusion dies or hot runners in injection molding. For this, flow path lengths and channel diameters in a manifold system are defined identical on all paths and thus those channels are considered to be identical in pressure drop and cavity filling, respectively in mass flow distribution. However, the changes in direction of the melt flow due to the deflection of the melt are in most cases neglected but have a significant impact on the flow field in downstream components. Strong deflections, as they occur in conventional manifold systems, can be avoided by the use of additive manufacturing methods. However, the bionic design leads to curved melt channels which, when naturally balanced, may differ completely from one another regarding their overall course and curvature. Therefore, unequal mass flow distributions or cavity fillings occur in such geometries. The aim of this paper is to investigate the influence of channel curvature on the balancing of additively manufactured melt channels. For this purpose, a test specimen is designed and the curvature collectives along the neutral fibers are evaluated. The overall objective is a more specific balancing with respect to the mass flow distribution. The results indicate the necessity of considering the channels’ curvature in the designing process in order to achieve a homogeneous melt distribution.