Melt front surface asperity and welding-defect generation in ceramic injection molding

Melt front roughness was examined firstly, and it was found that an injected part is separated into two regions: a rough surface region and a fine surface region. The rough surface region results from melt front asperities generated by the blowout of voids at the front surface which are mixed into the material by jetting flow in the sprue. It was also found that voids in the sprue can be eliminated by applying counter-pressure. Secondly, the generation property of welding defects, weld line and voids, has been examined by counter-flow joining and their elimination criteria are obtained. It was shown that both criteria approximately coincide with each other. The welding-defect elimination criterion obtained is applied to the evaluation of welding-defect generation under various injection conditions and it was found that the criterion does not depend greatly on the asperities of the flow front. Furthermore, the criterion is also effective for estimating welding defects in injection molding using a mold cavity with inserts. Finally, it was confirmed that the above criterion approximately coincides with that in a previous paper which was obtained by the use of simple void-reducing conditions in the joining of green ceramic blocks with artificially grooved surfaces.