INFLUENCE OF MOLDING VARIABLES ON DEFECT FORMATION AND MECHANICAL STRENGTH OF INJECTION-MOLDED CERAMICS

Defects such as voids and cracks were found in ceramic injection moldi ngs when the molding variables were not properly tuned. A factorial ex periment revealed that the formation of the macroscopic defects was re lated to the melt temperature of the feed-stocks in the injection barr el. Using a melt temperature significantly higher than the evaporation -starting temperature of the type of lubricant used (e.g. stearic acid ) presents a propensity to introduce voids. An improper selection of t he molding variables such as the hold pressure, the injection speed, a nd metering stroke, was found to aggravate the molding integrity by th e formation of cracks in addition to the voids. The cause for the occu rrence of these macroscopic flaws in the ceramic injection moldings ar e discussed. (C) 1998 Elsevier Science S.A. All rights reserved.