In the last decade, the development of fine-grained materials and investigations of the effects of the grain size on metal forming on a microscale have been carried out. However, there are few studies on the effects of the grain size on the metal forming process from the viewpoint of industrial manufacturing. In this study, we investigate the effects of the grain size on the micropiercing process as a continuous industrial process. 5,000 shots of piercing for each material were carried out, and the piercing forces during the punch penetration, the scraps produced and the hole conditions after piercing, and punch surfaces after iterative piercing processes were measured to evaluate the effect of grain size on the micropiercing process. Higher piercing forces were observed with smaller grains. The rate of increase of the force during 5,000 shots shows the same tendency. On the other hand, the variance of the piercing force is smaller for finer grained material and as a result, materials with smaller grains show higher quality on the basis of the scraps produced and hole observation. However, the volumes of tool ware and adhesives around the punch increased faster with smaller grains. Therefore, the selection of an appropriate grain size is necessary in industrial manufacturing.

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Thermal properties of Cr-Cu for heat-sink application are required to be close to those of Mo-Cu and W-Cu. The rolled and Cu-clad and rolled Cr-Cu infiltrated compacts are investigated to improve the thermal properties. In the rolled Cr-Cu material, Cr phases are significantly elongated and flattened, resembling a fibrous structure. Such a fibrous structure of Cr phases makes the thermal expansion coefficient much lower than that predicted from the rule of mixture. While the flattened Cr structure promotes thermal flow in the in-plane direction, it deteriorates that in the thickness direction. To improve thermal conductivity in thickness direction, the Cr-Cu compact was bonded with a Cu plate and rolled. The clad and rolled structure enables the improvement of thermal conductivity in the thickness direction without degrading the thermal expansion coefficient in the rolling direction.

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