Investigation into the effects of weld zone and geometric discontinuity on the formability reduction of tailor welded blanks

Numerous advantages of application of tailor welded blanks (TWBs) in automobile industry, namely reduction of weight, fuel consumption and air pollution, have made the manufacturers eager to investigate in this field. On the other hand, while experiments generally provide valuable information in regard with mechanical behaviors, but utilization of simulation methods has extended vastly due to time and cost saving issues. One challenging issue in numerically analyzing the forming behavior of transversely welded TWBs, welded by laser welding methods, has been the presence of weld zone. While some researchers believe that during simulation, the weld zone can be neglected due to its minority and consequently the simulation time will be less, the others confess that the consideration of weld zone increases the accuracy of the results although the time of simulation enhances. In this research, the effect of weld zone presence on the formability of transversely CO2 laser welded TWBs was studied experimentally and numerically (FE-method). The studied TWBs were consisted of IF-steels with different thicknesses (0.8 and 1.2 mm), and limiting dome height as well as forming limit diagram were used for formability assessment. Experiments in regard with limiting dome height test showed that the decisive factor in decreasing the dome height is geometric discontinuity and the effect of weld zone is about 6%. Moreover, simulation results indicated that the consideration of weld zone did not have any observable effect on limiting strains, although tearing occurred at lower punch stroke.