Springback characteristics of tailor-welded strips in U-draw bending

The purpose of this study is to investigate the springback characteristics of tailor-welded strips in U-draw bending. Two different welded strips were adopted to compare the effects of weld-line locations on the springback. One was welded along the centerline of the strip-width and the other was welded along the centerline of the strip-length. To investigate the effect of different thickness combinations on the springback, the tailor-welded strips were joined by a laser welding process. Three sheet thickness combinations were assessed, SCP1 0.8 t * SCP1 1.2 t, SCPl 0.8 t * SCP1 1.6 t and SCP1 0.8 t * TRIP 1.0 t. Three punch profile radii of 3, 6, and 9 mm and three die profile radii of 5, 10, and 15 rum were prepared and three blank holding forces (BHF) of 125 kg(f), 250 kg(f), and 500 kg(f) were applied to investigate the effects of punch profile radius (R-p), die profile radius (R-d), and BHF on the springback of tailor-welded strips. With consideration for the thickness of the sheet and the material properties, the extent of the springback on the sidewall of unloaded sheet shapes increases as the thickness and the yield strength of the sheet increase in the U-draw bending process. For longitudinally welded strips, the amount of springback of the TRIP steel sheet in TWB could be reduced through a springback combination of the thinner side and weld-fine. For the thinner side (0.8 t) of the centrally welded strips, the deformed shapes after the springback were almost the same regardless of the thickness combination, and the extent of the springback decreased compared with that of non-welded SCP1 0.8 t. Some experimental results are compared with analytical results obtained by using the finite element method.