Effect of ultrasonic attenuation characteristics on forming accuracy of ribbed cylindrical parts in ultrasonic-assisted spinning process

Ultrasonic-assisted forming process is one of the important methods to improve the formability of materials because of its acoustic softening effect and antifriction effect. After the introduction of ultrasonic, the forming accuracy of the inner ribs is improved in the spinning process of ribbed cylindrical parts, but the effect law of ultrasonic energy on the forming of inner ribs has not been clarified in detail. In this paper, a modeling method of ultrasonic-assisted spinning was proposed, which was taken into account the attenuation characteristics of ultrasonic energy in solid media for the improvement of the simulation accuracy. The corresponding simulation model was established to explore the effect law of ultrasonic amplitude on the forming accuracy of inner ribs. The results showed that the forming height and surface morphology of longitudinal ribs can be improved effectively in the ultrasonic-assisted spinning process. With the increase of ultrasonic amplitude, the forming height of longitudinal rib gradually increased, but the increase degree of the rib height gradually slowed down, and the difference of the material filling between the screw-in end and the screw-out end at the rib groove gradually decreased, but the surface morphology of the longitudinal ribs always present the geometric characteristics that the screw-in end is higher than the screw-out end. The reason is that the application of ultrasonic vibration promoted the radial and circumferential flow of the material and improved the material filling ability into the rib groove. The combined effect of ultrasonic softening effect and anti-friction effect reduced the radial filling difference between the screw-in end and the screw-out end of the ribs. Ultrasonic vibration could enhance the material flow but did not significant change the forming distribution characteristics of the ribs, resulting in limited rib height and uneven surface morphology. Also, the energy field gradient design method along the sheet thickness was proposed to further improve the forming accuracy of the inner ribs.