Forming mechanism of defects in spinning of large complicated thin-wall aluminum alloy shells

The spinning of large complicated thin-wall aluminum alloy shells is a multi-pass complex nonlinear plastic process under the effects of multi-parameters and their interactions. In the progress, defects such as backward extrusion, bulging, rupture are prone to occur. In this study, the forming mechanisms of these defects were investigated by experiments and finite element simulation. The results showed that excessive wall thickness reduction caused the metal bulge before the rollers, which was the main reason for backward extrusion, bulging, ring stripping and rupture. And excessive rotational speed of mandrel caused rupture and fish scale peeling. Moreover, some measures were proposed to avoid these flaws. The wall thickness reduction less than 24% was adopted to avoid the metal bulge before rollers. The rotational speed of mandrel was limited to avoid fish scale peeling and rupture in circumferential direction. Using these measures, qualified large complicated thin-wall aluminum alloy shells were formed.