An Experimental and Numerical Investigation of Deformation Mechanics on Hole-Flanging Process of AA6061- T6 Sheets through Single-Point Incremental Forming

Incremental forming process, as one of the methods used for forming complex parts in rapid prototyping, has various applications in the automotive and aerospace industries. The incremental forming process can be used to flange a metal sheet that, compared to conventional flanging, not only increases the formability but also does not require expensive dedicated dies. The deformation and damage mechanisms in the incremental forming process are completely different from conventional forming processes and need exact and thorough investigation. The present study is aimed at evaluating the damage and deformation mechanics in the hole-flanging process by single-stage and multistage incremental forming on AA6061-T6 sheets, considering several parameters affecting damage and fracture, including equivalent plastic strain, stress triaxiality, and lode angle parameter. These important parameters can reveal the stress and strain states as well as the deformation mechanism, which have been less addressed in the hole-flanging by incremental forming. The results indicated that the stress and strain states varied in different regions of the flange wall, such that the strain state was as plane strain at the bottom of the wall in contact with the unformed part of the sheet, biaxial tensile state at the middle of the wall, and uniaxial tensile state at the top of the wall on flange edge. The highest damage was observed at the flange edges, and the fracture occurred at low values of stress triaxiality in this area, indicating the shear fracture in the hole-flanging of AA6061-T6 sheets during the incremental forming. Finally, a slight increase was observed in the forming limit by forming with a multistage strategy instead of the single-stage one, although the equivalent plastic strain increased significantly.