A modified thin-walled tube push-bending process with polyurethane mandrel

Thin-walled (D/t > 30; D, initial outer diameter; t, initial wall thickness) bent tubes with large diameter (D > 100 mm) and small bending radius (R/D < 3; R, centerline radius) are difficult to form integrally using traditional bending methods. In this paper, using a novel loading method, a modified push-bending (MPB) process with polyurethane as mandrel was developed. A stainless steel bent tube with extreme geometrical specification (D = 144 mm, D/t = 72, and R/D = 1.94) was formed integrally by MPB. Based on analytical and finite element (FE) method, the internal pressure, i.e., contact pressure between polyurethane and tube (CPPT) were investigated. The results show that the CPPT decreases linearly from the back end to the front end of polyurethane rod and increases with smaller μ1 (the coefficient of friction between polyurethane and tube) and larger L (the center axis length of polyurethane rod), and the increase of CPPT is helpful to decrease the ovality of the bent tube.