The forming limit of stainless steel cups was improved by ironing using a pulsating motion generated by Numerical Control (NC) servo press. Although the limiting ironing ratio of an austenitic stainless steel SUS430 cup for a conventional crank motion using a press oil including a chlorine extreme-pressure additive was about 17%, the ratio was improved to 30% by the pulsating motion. The limiting ratios with and without the additive for pulsating ironing were similar. Pulsating ironing was also effective in improving the limiting ironing ratio of austenitic stainless steel SUS304 cups. A ring-shaped pattern was formed on the sidewall of the ironed cup by the pulsating motion, caused by the difference in surface roughness between portions ironed once and twice. Pulsating ironing not only improves the ironing limit but also eliminates the use of additives with high environmental impact.

One of the authors confirmed that the flexible rocking motion induced by controlling four linear actuators effectively reduces the forging load. In this study, this technique was applied to die forging, and load reduction and the improvement of die filling were investigated. A cylindrical aluminum specimen was upset into a rectangular-hole die, in which a rocking motion was applied to the punch in the latter half of the stroke. Experiments were conducted by varying the diehole shape, rocking conditions and the amount of compression. The upsetting load obtained when applying a rocking motion with high frequency and small angle was reduced by approximately 50% compared with that without a rocking motion. Die filling around the rocking tool was promoted, resulting in non-uniform die filling along the compression direction. Total die filling was mainly affected by the amount of compression. The rocking direction and the side-length ratio of rectangles caused little differences in forging load and die filling.