Metal Powder Injection Molding Research Articles

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

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.

Static pressure distribution in a powder-binder 2-phase medium

Because of its high potential for near-net shape manufacturing, metal powder injection molding (MIM) has attracted a growing attention recently. The MIM technique generally consists of the following four processes: metal powder-liquid binder mixing, injection of mixed medium into molds, debinding and sintering. Each MIM process has its peculiar problems to be overcome. This study is one of the approaches for obtaining clues for the optimization of the injection (molding) process, in which the mechanical properties of mixed 2-phase medium play an important role. This medium is supposed to have a unique properties for pressure transmission behavior, where Pascal's principle of isotropic pressure transmission may not be applied. That is, the pressure in the horizontal direction is not always equal to that in the vertical direction. In this paper a model for the pressure transmission property of the mixed 2-phase medium is considered. The present model predicts a variety of pressure distributions, depending on the parameters set considered here. The model reduces to Janssen's formula when the medium consists of solid particles and to the well known hydrostatic pressure distribution when it consists of liquid. In addition to theoretical work, a preliminary experiment is carried out. The experimental results seem to support the basic idea of the model.

金属粉末の射出成形における金属粉末に対する滑剤の影響

金属粉末の射出成形における金属粉末に対する滑剤の影響

金属粉末射出成形の動向

金属粉末射出成形の動向