The nanometric control in tool cutting edge sharpness of microtools when micropunching austenitic stainless steel SUS304 was investigated in this study. To achieve stable grain deformation and strain-induced martensitic transformation, an argon ion irradiation beam for finishing the cutting edge of a micropunch of nanometric size was developed. Firstly, micropunching was performed with normal ground tools and ion-polished tools. Secondly, the process affected zones existed in the vicinity of the punched hole were investigated by electron backscatter diffraction (EBSD). Moreover, the effects of differences in the tool cutting edge on grain deformation and strain-induced martensitic deformation were discussed. We found that ion-polished tools can effectively reduce grain deformation and strain-induced transformation.

A mechanical joining process of taper nuts and bolts to ultra-high strength steel sheets by punching was developed, because resistance projection welding generally used for joining of nuts and bolts has low joinability for the ultra-high strength sheets. In this process, the sheet is punched with the taper nut and bolt, and the nut and bolt are joined by ironing and expanding the punched hole. The upper surfaces of the nut and sheet are aligned by controlling the stroke in order to attach other parts. No pre-punching is required for the sheet, whereas higher strength than the sheets is necessary for the nuts and bolts. For the die-quenched steel sheet having a tensile strength about 1500 MPa, the joint strength was about two times higher than that specified in the Japanese Industrial Standard of weld nuts. For the sheets above 780 MPa in tensile strength and above 1.6 mm in thickness, sufficient joint strength was obtained.

In general, Ti-6Al-4V alloy sheets are formed by incremental press forming in the temperature range between 600 and 900 ℃. In this temperature range, the ductility of Ti-6Al-4V alloy is improved. Because of the low ductility of Ti-6Al-4V alloy at temperatures between room temperature and 600 ℃, fracture easily occurs during press forming. Hence, a method of press forming of Ti-6Al-4V alloy sheets between room temperature and 300 ℃ was developed. In this method, the punch motion and blank holding force were applied separately until the maximum punch load was reached to prevent fracture at the punch shoulder. The drawing process was carried out from the maximum punch load until finish forming to prevent fracture at the end of the flange. In addition, by applying the developed method, we were able to prevent the decrease in thickness at the punch shoulder, compared with the case of press forming. As a result, warm press forming of Ti-6Al-4V alloy sheets at 300 ℃ was achieved by applying the developed method in experiments and finite element analysis.