Method for establishing and using forming limit diagram of laser tailor-welded blank

The invention discloses a method for establishing a forming limit diagram of a laser tailor-welded blank. The method comprises the following steps: (A) establishing an XY coordinate system of which the X represents a direction perpendicular to the direction of a welding seam and the Y represents the direction parallel to the direction of the welding seam; (B) calculating an ultimate strain of a material in a welding zone by adopting an empirical formula and combining with performance parameters of the material, and then, based on stress strain relation of the material in the welding zone and weak side parent metal, calculating to obtain weak side parent metal FLC by combining with the performance parameters of the weak side parent metal when the material in the welding zone is invalid, namely, Y-direction strain is larger than X-direction strain; (C) calculating the weak side parent metal FLC when the weak side parent metal is invalid, namely, the Y-direction strain is smaller than the X-direction strain by a