An investigation on multistage incremental forming to control thinning in a truncated cone of an aluminum alloy sheet

The single point incremental forming, which is appropriate for low volume production, is one of the simplest varieties of incremental sheet metal forming process. One of the critical issues with single point incremental forming is excessive thinning which affects the strength of the part and confines the applicability of the process to produce only parts with small wall angle. In this paper, multistage single point incremental forming of a truncated cone with 70° wall angle made from an aluminum alloy sheet is studied to alleviate excessive thinning. By proposing a new two-stage forming strategy and obtaining the corresponding parameters using an appropriate algorithm, it is shown that thinning and forming time can be improved through a systematic design of multistage forming. The implementation of the designed two-stage single point incremental forming leads to less thinning in the part when compared to either the two or three-stage single point incremental forming based on a conventional strategy. The bulging at the bottom of the part, which is one of the drawbacks of multistage single point incremental forming, can also be controlled by using the proposed strategy.