Experimental and numerical study on the deformation mechanism of straight flanging by incremental sheet forming

摘要

The geometric accuracy is a key quality indicator for the application of flanging by incremental sheet forming (ISF), namely incremental flanging (IF). As a local loading forming process, the deformation process in IF is different from that in conventional flanging formed by press-working operation in which considerable geometric error can be introduced. Thereby, the deformation process of straight flanging by ISF is investigated through both experimental and numerical simulation approaches. First, the effects of different yield functions (Mises and Hill48) and hardening models (A-F, isotropic and kinematic) on the prediction accuracy are investigated. In particular, the Hill48 yield function is not only solved by r-values, but also calibrated by material properties of strain states corresponding to the actual deformation condition of straight flanging by ISF. Among different yield functions, calibrated methods and hardening models, a A-F hardening model with the calibrated Hill48 yield function is found to have the best performance in terms of prediction accuracy of both forming force and cross-section profile. Then, based on this model, the deformation process of the straight flanging by ISF is analyzed. The results show that the strain states of straight flanging by ISF are plane and uniaxial tension strain states. In the forming process of straight flanging by ISF, the whole blank experiences bending-unbending deformation in which the material contacting with the die undergoes reverse loading. In addition, the main deformation modes of straight flanging are bending and stretch deformation through internal energy analysis. Finally, the deformation process of the straight flanging by ISF is theoretical analyzed. It is found that the elastic moment in the reverse loading mode is the main source for geometric error of the straight wall.