Investigation on the material flow and deformation behavior during ultrasonic-assisted incremental forming of straight grooves

The introduction of ultrasonic vibration is proved to be beneficial for the reduced force and improved formability for sheet forming processes. However, the vibration-induced material behavior is still not satisfactorily explained. The objective of this work is to investigate the effect of the ultrasonic vibration on the material flow characteristics and the plastic deformation mechanism during the incremental sheet forming of the straight groove. Both analytical and finite element models are established to explore the impacts of ultrasonic amplitude, frequency, step-down size and feed rate on material flow characteristics. It was found that the material flow area was dramatically increased after applying the ultrasonic vibration, and the influence of ultrasonic amplitude on material flow area is greater than that of frequency, which is similar to the effect of acoustic softening. In addition, the separation effect under different amplitudes and frequencies was analyzed through finite element modeling to partly explain the reduction of forming forces. The duty cycle was decreased as the amplitude increases as well as the frequency. Furthermore, the material flow behavior and the force reduction rate for different tool paths are explored. Finally, experiments were performed which further verified the reliability of the analytical and FE models. These findings provide a theoretical basis for further investigation of the mechanisms of ultrasonic-assisted incremental sheet forming process.