Research on the axial elongation and springback law of thick-walled tubes in cold bending forming

The axial elongation and springback problems of tube bending need to be solved respectively, to realize the "no allowance bending" and "flange welding prior to bending" processes for ship thick-walled tubes. The axial elongation and springback analytical models of the tube bending process are established respectively based on the force balance condition, comprehensively considering the influence law and mechanism of geometric and material intrinsic parameters. The relationships between the axial elongation and forming angle, the bending angle, and forming angle are found respectively. A formula for calculating the start bending point position of the tube is obtained according to the geometric relationship after springback. The finite element (FE) model of the thick-walled tube is established based on the ABAQUS platform; the processes of tube bending and springback are simulated. The accuracy of the established FE model and theoretical analysis models is verified through tube bending experiments. The influence of main process parameters on the axial elongation and springback of the tube bending is analyzed. The results show that for tubes with the same materials, in the scope of engineering application, both the axial elongation and the bending angle have linear relations with the forming angle, and they are not through the origin of the coordinate; the axial elongation of the tube bending increases with the increasing of the forming angle; the springback angle increases with the increasing of the bending angle. At last, the applications of axial elongation and springback law are proposed.