An analytical springback model for bending of welded tube considering the weld characteristics

Predicting springback is important for improving the precision of tube bending forming. Compared with a homogeneous tube, the springback of a welded tube is more complex owing to the uneven material properties and geometric characteristics. An analytical springback model for welded tube bending was established according to the static equilibrium condition, with the aim of improving the prediction accuracy for the welded tube springback. In this model, the continuous variations of the weld material properties and the anisotropic parameter (contractile strain ratio), as well as the effect of the weld position were considered. Using the model, the springback angles of a QSTE340 welded tube in numerical control bending were predicted. Comparisons with experimental results suggest that this springback model can accurately predict the springback angle and present higher prediction accuracy than the existing models. In addition, the influence of description exactitude about the weld material property on the prediction accuracy was analyzed. The results suggest that the continuous weld material model adopted can significantly improve the prediction accuracy, and the improvement degree varies with the position of weld during bending. Finally, the effects of the mechanical properties matching between the weld and parent metal and the geometric parameters of the welded tube on the springback were determined using the established springback model.