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Effective experimental method for identification of the forming limit diagram of sheet metals (금속 박판의 성형한계도를 구하기 위한 실험방법 개선에 관한 연구)
An effective experimental method is developed and carried out for identification of the forming limit diagram(FLD) of sheet metals. The sheet metals used in the experiment are several kinds of cold rolled steel sheets for autobody stamping. The FLD's are constructed from the specimens fractured during deep drawing and stretch forming, controlling width of the specimens and lubrication conditions. During the process of deep drawing, the blank holding force was controlled and a rubber pad was occasionally used to prevent excessive draw-in. The FLD's constructed by the experiment are compared with the theoretical ones. The theoretical FLD's are constructed by the data of mechanical properties obtained from the uniaxial tension test. A particular forming limit band is constructed based on the experimental data with both deep drawing and stretch forming. This forming limit band assures the formability of steel sheets during the stamping process for autobody, providing the limit strains in both stretch forming and deep drawing.