Springback Evaluation of Tailor Welded Blanks at V-die Bending made of DP Steels

Abstract

This study presents the experimental results and the comparison of different analytical models for springback evaluation of bent thin sheets. Three types of advanced high strength steels (from the group of dual phase steels, namely DP600, DP800 and DP1000) and a mild steel (DC04) were used to investigate the sheet profile after rectangular V-die bending. Uniaxial tension-compression tests were also carried out formerly to lay the basis of the precise theoretical examinations. Striving to consider all possible circumstances, the change of the elastic modulus with the increase of the plastic strain, as well as plane strain state with the corresponding yield stress were assumed during the springback prediction. In certain cases, the effect of the sheet thickness variation was also taken into account. In many practical stampings, these variables can be at least partially neglected, but the presented models also can lead to poor accuracy, even though they are more complicated. According to our experiences, both the circular approximation and the moment-equilibrium based general formulae predict under the measured springback angles, but the punctuality can be developed by precise material behavior modelling. The phenomenological approach extended with fitting parameters gives the most accurate estimation obviously, but the physical meaning of the added parameters remain a question. The uncertainty is being more enhanced at the tailor-welded blanks (TWBs) where the interaction of the components should not be negligible as well, i.e. a subsequent variable, namely the distance from the weld line comes into the focus. Laser beam welding was applied to joint each DP steels to the mild steel component and then the sheets with different widths were bent perpendicular to the weld line. Due to the doubled effect on the deforming or restraining action of the different sides, the final shape and thus the curvature shift towards the weld line from the blank’s edge. It means that new viewpoints need to consider at the analytical springback evaluation of TWBs.