Novel approach to decrease sheet thinning during sheet metal forming by using embossing technique

摘要

Embossing technique allows strengthening properties of sheet metal materials to be specifically increased. This increase in strength results from strain hardening and residual stresses, which are induced into the sheet metal material during the embossing process and thus locally influence mechanical properties such as yield and tensile strength. As a result, not only the final properties of sheet metal components can be modified, but also the formability of semi-finished sheet metal products can be influenced. Concretely, the local strengthening can significantly improve the force transmission in sheet metals during deep drawing and thus enlarge the process window. In the FEM study presented in this paper, dual-phase DP600 grade steel sheets having a thickness of 1.2 mm were subjected to near-surface unilateral embossing. Subsequently, these embossed steel sheets were used to investigate the influence of different embossing patterns and embossing depths on the critical areas appearing during deep drawn of a cylindrical cup. In order to evaluate the effects of the focused embossing parameters on the forming behavior, Nakajima tests were additionally performed with embossed sheet specimens. An essential finding of this study is that the local increase in yield strength contributes to preventing premature sheet thinning in the force transmission zones and avoid split formation in early stages of a deep drawing process.