Analysis of Forming Process of Automotive Aluminum Alloys Considering Formability and Springback

Formability and springback of the automotive aluminum alloy sheet, 6K21-T4, in the sheet forming process were numerically investigated utilizing the combined isotropic-kinematic hardening law based on the modified Chaboche model. To account for the anisotropic plastic behavior, the non-quadratic anisotropic yield stress potential, Yld2004-18p was considered. In order to characterize the mechanical properties, uni-axial tension tests were performed for the anisotropic yielding and hardening behavior, while uni-axial tension/compression tests were performed for the Bauschinger and transient behavior. The Erichsen test was carried out to partially obtain forming limit strains and FLD was also calculated based on the M-K theory to complete the FLD. The failure location during simulation was determined by comparing strains with FLD strains. For verification purposes, the automotive hood outer panel was stamped in real. After forming, the amount of draw-in, thinning and springback were measured and compared with numerical simulation results.