Theoretical and experimental investigation progress on the forming limit of sheet metal forming

Forming limit is the most important formability index and process parameter in sheet metal forming. On the basis of the expatiation on the effects of forming limit to the research and application of sheet metal forming, this paper overviews and analyses the theoretical and experimental investigation progress on the forming limit. FLD is remarkabaly affected by the strain paths, which brings the inconvenience to industry. And the forming limit stress diagram which established with limit stress is independent on the strain paths and it is more convenient and practical to use as the criterion of forming limit under complex strain paths. Therefore, the research of the FLSD combined with FLD becomes the hotspot and one of main approaches to establish the limit criterion accurately. The cruciform biaxial tensile test is an effective and practical method to realize the process of complex strain paths. Finally, the pivotal question is expounded for the FLSD and the cruciform biaxial tensile test.