Effect of weld characteristics on the formability of welded tubes in NC bending process

The weld profiles, weld width, weld positions, and mechanical property changes in the weld and heat-affected zones (HAZ) are the most important parameters that influence the potential formability of the welded tube. To investigate the effect of weld characteristics on the forming behaviors of the welded tube, finite element models which consider the geometric profile and mechanical properties of the weld and HAZ are employed. The results show that (1) the mechanical constitutive relation of the weld region determined by the microhardness empirical formula obviously decreases the tangent strain, thickness strain, and cross-sectional deformation ΔD in the weld and HAZ as compared with that determined by the improved rule of mixtures, which is contrary to the hoop strain, and the predicted results determined by the improved rule of mixtures are much closer to the experimental ones; (2) different weld and HAZ widths determined by the microhardness profile and metallographic section have a little effect on the tangent strain, thickness strain, and ΔD distribution; (3) the implementation of weld profile and material properties decreases the wall variation of the weld region as the weld line locates on the outside and inside. On the contrary, both the weld profile and weld material properties increase the maximum ΔD. The sectorial weld profile has a stronger effect on the wall variation and maximum ΔD than the hourglass profile; and (4) the same weld and HAZ volume have a stronger effect on wall thinning and ΔD.