Criteria for Outward Curling of Tubes

Abstract

The criteria for outward curling of circular metal tubes have been investigated experimentally and theoretically. The results are summarized as follows: (1) The critical bending radius, ρc exists. When the bending radius at die inlet ρ is larger than the ρc, the tube end fits well on the die surface. On the other hand, when ρ ≤ ρc, the tube end separates from the die surface and curling occurs. (2) It is found that there is a geometrical similarity law of the ρc. The ρc increases with increasing die angle. Furthermore, it is also clarified that the ρc is independent of the tube materials and lubrication.