Application of combined process of holding pressure and ultrasonic vibration to control the springback behavior of pure titanium foils

Foil bending is one of the promising approaches to fabricating micro-bending parts. However, it is difficult to bend pure titanium foils with high precision due to the double effect of size effects and close-packed hexagonal crystal structure. To control the springback behavior of pure titanium foils, an ultrasonic vibration-assisted bending platform was developed, and the mechanism by which ultrasonic vibration affects the springback behavior was investigated. The results indicate that the compressive stress induced by ultrasonic vibration has a plastic penetration effect, which forces the hard-oriented grains to deform and eventually changes the stress distribution state of the bending region. Therefore, both the amount and the scatter of springback decrease with increasing ultrasonic amplitude. The surface roughness of foils with a t/d value of 5.4 decreases by 42.4% under ultrasonic vibration. However, ultrasonic vibration is effective in controlling the spring-back behavior only at the initial stage (0–5 s), so there is no need to extend the ultrasonic vibration time substantially. The plastic penetration capacity of compressive stress can be greatly enhanced by applying holding pressure, so the combined use of holding pressure and ultrasonic vibration is a useful process to control the bending springback behavior of foils. This work provides a basis for the efficient and precise fabrication of micro-bending parts.