Increasing the Formability of CP-Ti during Incremental Sheet Forming with an Auxiliary Sheet

As a flexible sheet metal forming process, incremental sheet forming (ISF) has been extended to fabricate lightweight sheet metal components, and increasing the formability is one of the key topics. In the present work, a novel ISF process integrating an auxiliary sheet (ISF-AS) is proposed for the improvement in formability, and investigated by using commercially pure titanium (CP-Ti) as the target sheet (TS). The experimental results demonstrate that the fracture strain obtained by ISF-AS process is increased by 50.6% compared with conventional ISF (CISF), and the geometric accuracy by ISF-AS is less than that by CISF. To explore the deformation mechanism during ISF-AS process, an analytical model of stress triaxiality based on membrane analysis has been developed, which demonstrates that ISF-AS can further increase the hydrostatic compression stress and reduce the stress triaxiality of TS compared with CISF. The fracture morphologies indicate that the dimples by CISF and ISF-AS processes are both elongated along the circumferential direction, but there are more tiny dimples with uniform distribution on the fractured surface of ISF-AS. In addition, orange peels on the lower surface of the part can be obviously restricted by ISF-AS with the improved surface quality.