Characterization of Residual Stresses in Conventional Forming and Hydroforming of Tailor Welded Blanks

Residual stresses in sheet metal components depend on the forming technique and the history of load path changes during the process. Characterization of residual stresses in the case of tailor welded blanks (TWBs) is challenging due to the differences in thickness and/or plastic deformation behavior within the blank. In the present work, the forming outcome is evaluated based on the final residual stress distribution in the formed TWB specimens. The methodology is demonstrated by biaxial stretching of TWBs of interstitial-free (IF) steel and draw quality (DC01) steel under two different processing routes (conventional forming and hydroforming). The numerically predicted residual stresses are observed to be lower and more uniformly distributed in the case of hydroforming when compared to conventional forming. The negligible residual stresses (or less tensile near the weld zone) in the hydroformed parts can be advantageous in the automotive industry leading to an improved life. The weld zone properties play an insignificant role in the distribution of predicted residual stress in biaxial stretching of TWBs. The numerically predicted results are validated experimentally using the x-ray diffraction technique. The agreement between numerical and experimental results is better in hydroforming than in the case of conventional forming.