Papers by Author: Kazuaki Nishiyabu

Abstract: A novel production method for porous metal components has been developed by applying powder space holder (PSH) method to metal powder injection molding (MIM) process. The PSH-MIM method has an industrial competitive advantage that is capable of net-shape manufacturing the micro-sized porous metal products with complicated shapes and controlled porosity and pore size. In this study, the small impeller with homogeneous micro-porous structure was manufactured by the PSH-MIM method using porous compounds composed of fine stainless steel 316L powder and polymethylmethacrylate (PMMA) particle. The effects of combinations in size and fraction of PMMA particle on dimensional tolerance and variation of sintered porous specimens were investigated. It was concluded that the PSH-MIM method could manufacture commercially micro-porous metal components with high dimensional accuracy.

Abstract: This study aims to investigate the effects of hybrid micro/nano powders in a micro metal injection molding (μ-MIM) process. A novel type of mixing-injection molding machine was used to produce tiny specimens (<1mm in size) with high trial efficiency using a small amount of feedstock (<0.05cm3 in volume). Small dumbbell specimens were produced using various feedstocks prepared by changing binder content and fraction of nano-scale Cu powder (130nm in particle size). The effects of adding the fraction of nano-scale Cu powder on the melt viscosity of the feedstock, microstructure, density and tensile strength of sintered parts were discussed.

Abstract: The production method of micro sacrificial plastic mold insert metal injection molding, namely μ-SPiMIM process has been proposed to solve specific problems involving the miniaturization of MIM. The sacrificial plastic mold (SP-mold) with fine structures was prepared by injection-molding polymethylmethacrylate (PMMA) into Ni-electroform, which is a typical LIGA (Lithographie-Galvanoformung-Abformung) process. Stainless steel 316L feedstock was injectionmolded into the SP-mold which had micro structures with multi-pillars. The green compact was demolded as one component with the SP-mold, which was decomposed along with binder constituent of feedstock in debinding process. This study focused on the effects of metal particle size and processing conditions on the shrinkage, transcription and surface roughness of sintered parts, which were evaluated by SEM (Scanning Electron Microscope) observation.

Abstract: Gas surface treatment is considered to be especially effective for Titanium because of its high reactivity. In this study, we investigated the gas nitriding mechanism in titanium sintered parts produced by metal powder injection molding (MIM) process. In MIM process, gas nitriding can be surface-treated subsequently after debinding and sintering process. Then, the microstructure and nitrogen content of sintered MIM parts are considered to be greatly influenced by not only nitriding conditions but also sintered conditions. In this study, the effects of sintering time on microstructure such as nitrided layer thickness and hardness was investigated. Focus was given to the effects of specimen size on nitriding process, because the size of micro metal injection molding (μ-MIM) product is so small and the specific surface of that product is so large that the mechanical and functional properties can be subject to change by nitriding.

Abstract: The production method for metal components with micro sized porous structure has been developed by applying “powder space holder method” to metal powder injection molding process. In this study, a co-sintering process was utilized to make a plate of sintered metal with micro porous graded structure. The green compact sheets with various contents of space hold particles were prepared by hot press molding for simplification. The five layers of metal with symmetric structure, which the skin layer was formed with high density metal and the core was formed with open or closed porous structure, or with inverse symmetry, was obtained by changing stacking sequence in co-sintering process. Mechanical properties of the materials with plain homogeneous porous structure and porous graded structure were compared. The usefulness of proposed method for producing the metal components with micro porous graded structure and the effective of graded structure to compensate the deficiencies on the mechanical property of porous metals was shown.