Reduction of friction in the guiding zone during tube hydroforming

In the tube hydroforming process, friction in the guiding zone often affects the axial feeding process. In this article, the effect of the main factors on friction force were analyzed first according to the force analysis model proposed. Based on the idea to reduce friction force by decreasing the contact area, a new punch structure was proposed. A testing tool was developed to evaluate the feasibility of the new structure. Results show that the length of the guiding zone, the stress state and the friction coefficient are three main factors that determine the effect of friction force. The ratio of friction force to punch load will increase rapidly as these three factors increase. By using the new sealing and guiding structure, about 30% of the punch load can be reduced. The use of a polyurethane ring in the gap between the tube and die can reduce friction force greatly if the bulge forming of the tube tends to occur in the guiding zone.