Flow Property and Defect Generation during Mold Cavity Filling Stage in Ceramic Injection Molding.

Generation of molding defects in ceramic injection molding, e. g. melt front asperity or surface roughness of an injected part, has been examined by using radial flow in a circular mold cavity. The following results were obtained. Firstly, it was found that an injected part is separated into 2 regions: region I with rough surface and region II with smooth and fine surface. The rough surface of region I results from a rough melt front, which moves to the mold surface and forms the surface of an injected part in the early filling stage. Secondly, front asperity is generated by the blowout of voids at the front surface, which are mixed into the material and by jetting flow. Voids in the sprue can be prevented by applying counter pressure. An injection molding method using a film gate with proper gap and a side gate is proposed. In this method, high pressure is applied to the filling material in the sprue to reduce voids, and it becomes possible to mold parts with smooth surfaces by removing voids in the sprue and jetting flow in the mold cavity.