investigation of forming limit and weld line movement in the forming of tailor welded blanks using experiment and numerical methods

the forming limit diagram (fld) is a useful method for characterizing the formability of sheet metals. in this paper, different numerical models were used to investigate the fld of tailor welded blank (twb). twbs were co2 laser-welded samples of interstitial-free (if) steel sheets with different thicknesses. the results of the numerical models were compared with the experimental fld as well as with the empirical model proposed by the north american deep drawing research group (naddrg). the emphasis of this investigation is to determine the performance of these different approaches in predicting the fld. these numerical models for fld are: second derivation of thinning (sdt), effective strain rate (esr), major strain rate (msr), thickness strain rate (tsr) and thickness gradient (tg). results of this research show necking will happen, when the value of msr, tsr, esr criteria is maximum, tg ≤ 0.78 and sdt criterion has the first peak in forming process time. weld line movement is one of parameters which influence formability of twbs. maximum of weld line movement of twb base on different numerical criteria was predicted and compared with experimental results. results of this research show that sdt criterion has a good accuracy for prediction of forming limit diagram and also weld line movement in the forming of twb.