53 巻 (2012) 622 号 p. 1013-1017
The formability of quenchable steel sheets in hot stamping was improved by preventing the decrease in the temperature of the flange portion of a formed cup. The effects of forming speed on the distributions of the temperature and wall thickness of the formed cup were examined in an experiment on hot drawing with a hemispherical cylinder punch. The decrease in the temperature of the flange portion caused by contact with a die and a blankholder was prevented by high-speed forming using a mechanical servo press. Thus formability was improved by decreasing the drawing resistance of the flange portion. To improve formability in low-speed forming using a hydraulic press, a spacer thicker than the blank was inserted between the die and the blankholder. The decrease in the temperature of the flange portion was prevented by decreasing the extent of contact with the die and blankholder owing to the gap generated by the spacer. In addition, the quenching of the flange portion was prevented by generating a gap to facilitate the trimming of the flange portion.