Formability improvement in single point incremental forming of truncated cone using a two-stage hybrid deformation strategy

In this research, a new hybrid forming strategy is proposed and investigated numerically and experimentally to improve the formability in single point incremental forming (SPIF). At the first stage, the hydraulic bulging of the sheet metal is performed under a specified fluid pressure to obtain an intermediate shape, then the fluid pressure is removed and the bulged sheet is inverted upside down. Finally, the SPIF of the truncated cone with a certain wall angle is carried out on the pre-bulged sheet. To this end, a die set was designed and manufactured. To study the deformation mechanics and the thickness distribution, finite element modeling using Abaqus/Explicit was employed. The maximum achievable forming depth and the thinning in the hybrid forming strategy were compared with those in the single-stage and the equivalent two-stage SPIF. Results of the 70 degrees wall angle cone show that by implementing the two-stage hybrid forming, the forming depth and the thinning can be improved by 26 and 45% compared to the single-stage SPIF, respectively. On the other hand, the equivalent two-stage SPIF can lead to an improvement of about 10% in the forming depth compared to the single-stage SPIF.