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The application of tailored blanks to autobody parts has progressed because of its numerous advantages. The forming of tailored blanks has, however, a lot of technical problems. Among the problems, weld-line movement and formability deterioration are the most significant ones in case of deep drawing. The weld-line movement and formability change were examined experimentally as a function of weld-line location in square cup deep drawing. The weld-line movement of tailored blank consists of two sources. One is the geometrical reason, and the other is due to the hardening of weld bead. The formability of tailored blank is inferior to that of an original blank by the existence of hardened weld region. The mode of fracture changes from wall breakage to a fracture adjacent to punch radius when the weld-line was close to the punch corner.

The forming limit diagram, which is widely used in the sheet metal stamping industry in developing new forming operations, is predicted from the plastic instability criterion proposed by Jun. Predicted forming limits are compared with the experimental data for several sheet steels that are important in the automotive industry. It is found that the predicted forming limits for the steels agree with the experimental results with reasonable accuracy in initial proportional loading and complex loading paths.