Deformation mode analysis of forming limit diagrams for tailor-welded blanks

This paper presents an analysis of deformation modes of Forming Limit Diagrams (FLDs) for tailor-welded blanks (TWBs) through designed experiments. Cold rolled steel sheets of different thickness combinations are used in this study. One-step forming of TWBs has the advantage of cost reduction and body weight reduction. Recently, TWBs are being commonly used in car-body panel manufacturing. Most of the previous research work focused only on the effects of laser welding parameters and material properties on the formability of the TWB. However, effects on the FLDs of TWBs are still uncertain. For this reason, a kick-off study on the analysis of different thickness combinations of 0.7mm, 0.8mm and 1.0mm steel sheets was carried out after butt-welding by Nd-YAG laser. Circular grid patterns were printed on the surface of specimens for different testing, like tensile testing and Swift Round-bottom testing. The experimental results show that the FLCs of TWBs are lower than those of base metals which indicates that TWBs have a lower formability than base metal. For TWBs with larger thickness combination difference, the failure occurred at the lower major strain ε1value, which implies that they have a lower formability. Hence, the FLD of TWBs should be beneficial to car-body panel manufacturing industry.