Experimental and theoretical investigation of thickness ratio effect on the formability of tailor welded blank

The influence of thickness ratio (TR) on the formability and forming limit diagram (FLD) of tailor welded blanks (TWB) obtained by pulsed Nd:YAG laser welding of St12 steel sheets are studied. Steel sheets with thicknesses of 0.5, 0.8 and 1.0 mm were combined to form TWBs of different thickness ratios of 2 (1.0/0.5 mm), 1.6 (0.8/0.5 mm) and 1.25 (1.0/0.8 mm). Limit thickness ratio (LTR) is introduced as a new useful factor for prediction of forming limit of TWB. Results of this research show that by increasing the difference of thickness ratio of TWB and LTR, formability and the level of FLD will decrease. In addition, effects of thickness ratio of TWB on the punch's load–displacement, limit dome height (LDH) and weld line movement are studied. By increasing the thickness ratio, the LDH decreases and some defects such as weld line movement and wrinkling increase. The experimental findings of this study show that the thickness ratio of TWB can effect on the position of fracture in TWB products.

► A comparative study between different forming limit diagrams (FLD) for tailor welded blanks (TWBs) was done in this research.
► Analytical ductile fracture criterion and some other forming limit criteria were investigated for necking prediction of TWB.
► Load–displacement of numerical criteria was compared with experimental results for different samples.
► Numerical criteria have a good agreement for load–displacement prediction with experiment.
► Advantages and disadvantages of numerical FLDs were presented.