2009 年 50 巻 580 号 p. 424-428
A hot gas bulging process for an aluminum alloy tube with resistance heating in a forming machine was developed. The tube was rapidly heated by electrifying to increase its formability and to decrease its flow stress. Since the tube was bulged by thermally expanding air sealed in the tube without controlling internal pressure during forming, the control became easy. The hot gas bulging of an aluminum alloy tube without and with axial compression was performed. The effects of the initial internal pressure and current on the expansion ratio of the tube were examined. The decrease in temperature around the contact with the electrode was prevented by inserting a stainless steel ring with low thermal conductivity and high heat generation between the copper electrode and the tube, and thus, the bulging length increased. The formability of the aluminum alloy tube was markedly improved, i.e., the expansion ratio at the onset of bursting for hot gas bulging was 130%, whereas that for cold hydroforming was 20%. It was found that hot gas bulging is effective in increasing the formability of aluminum alloy tubes.