Deformation characteristics and formability enhancement during ultrasonic-assisted multi-stage incremental sheet forming

Abstract

Although the multi-stage incremental sheet forming strategy is beneficial for manufacturing complex geometrical shapes via objective transitional stages, the forming limit and geometric accuracy are highly dependent on intermediate shapes, which need further improvement. Therefore, a novel forming strategy by combining the multi-stage sheet forming with ultrasonic-assisted vibration (UV) was proposed in the present work. This paper investigates the effect of ultrasonic vibrations on forming forces, thickness distribution, and stress–strain distribution through experimental tests and finite element (FE) simulations. Initially, a series of tests were conducted to determine the forming limit for three proposed strategies based on parameters including depth, initial diameter, and angle, both with and without the assistance of UV. Afterward, the FE model was established in ABAQUS/Explicit based on the optimal strategy by adopting the modified crystal plasticity constitutive model. The results indicated that, after superimposing the ultrasonic vibration, forming forces were effectively reduced and plastic deformation was greatly improved due to the increased equivalent plastic strain. Meanwhile, the application of the UV field efficiently reduces the high-stress zones and significantly decreases the stress value. Finally, it was discovered that by imposing UV at the appropriate forming stages, formability and thickness distribution can be successfully improved. The present investigation is beneficial to well understand the affecting mechanism of UV in completing the multi-stage sheet forming technique and obtaining the enhanced sheet formability.