Study of formability of aluminum truncated pyramid in single-stage and two-stage incremental sheet forming

Incremental sheet forming has already provided distinct advantages, such as inexpensive tools and the simplicity of the process, over conventional sheet forming processes. However, the method still has some limitations. Among these limitations, severe thinning has significant effects on the performance of the final product. Also, some parts with high wall angles cannot be formed by single stage incremental forming. To overcome these restrictions, multistage incremental forming can be implemented to achieve the desired wall angle, better thickness distribution, and the lower thinning. In this study, a two-stage incremental forming of an aluminum truncated pyramid with a wall angle of 70° was studied experimentally and numerically in order to improve the achievable minimum thickness. By introducing two-stage forming strategies and achieving their defining parameters using finite element simulation, the sheet thinning was compared to the one in the single-stage forming. Experiments were used to validate the finite element analysis. The results revealed that using the two-stage forming strategy, the minimum thickness can be improved twice than the one in the single-stage forming. A good agreement was observed between the thickness distribution obtained by experiments and predicted by the finite element modeling. Finally, the effect of forming strategies on the strain paths was investigated through the finite element simulation and the experimental fracture forming limit diagram.