Macroscopic mechanism of ultrasonic vibration in ultrasonic-assisted metal forming

Abstract

Ultrasonic vibration-assisted metal forming has gained increasing attention and applications recently, but the mechanism of ultrasonic effects is still not clear. In this paper, a new finite element method to simulate all ultrasonic effects in metal forming was proposed, and the volume effect and surface effect were quantitatively analyzed in upsetting and U-groove extrusion. It was found that the ultrasonic effects were quite different in upsetting and extrusion. In U-groove extrusion, the acoustic softening effect reduced the flow stress of the material by 20.0 MPa, far less than that in upsetting (91.7 MPa). The friction decreased by 82.7% due to the surface effect, which was more significant than that in upsetting (decreased by 58.3% and 33.3% at the top and bottom interfaces). Ultrasonic vibration increased the feature height in U-groove extrusion from 0.653 mm to 1.427 mm with a growth rate of 118.5%. The acoustic softening effect increased the feature height by 0.063 mm (8% of the total increase), while the surface effect increased the feature height by 0.711 mm (92% of the total). The surface effect plays a key role in affecting material flow in extrusion. It is suggested that this method could accurately reflect the deformation behavior of materials with ultrasonic assistance, and is of great value for process design and in-depth study of the microscopic mechanism in ultrasonic forming.

Keywords

• Ultrasonic vibration
• Plastic forming
• Numerical simulation
• Volume effect
• Surface effect