常圧及び加圧焼結のメカニズムとニヤネットシェイプ制御 ステンレス鋼圧粉体の焼結収縮挙動の数値解析

Abstract

Sintering shrinkage behavior is numerically simulated on stainless steel powder compacts prepared by metal powder injection molding (MINI). The MIM process is now highlighted because of its near-net-shape productivity of small mechanical parts having complex shape along with high relative density. In general, however, the initial packing density of the compacts is rather low to be around 55vol.% in relative density. This should cause large volume change during sintering, resulting in the possible nonuniform shrinkage in the compacts. Thus, in the MIM process, the prediction of geometric change of a compact is of extreme importance.The numerical simulation involves finite difference analysis to determine temperature distribution in a compact set in a vacuum furnace, densification analysis by use of sintering rate equations, and finite element analysis to convert the shrinkage into the geometric change of the compact. Six rate equations for sintering mechanisms summarized by M.F.Ashby are used for the calculation. We have assumed that the six mechanisms are distinguishable and sintering rate is the sum of the six rate equations. It has been demonstrated that the density inhomogeneities due to local temperature differences contribute to the nonuniform shrinkage in the early stage of sintering; however, it attenuates reversely in the final stage.