Ultrasonic-assisted microforming of superalloy capillary: Modeling and experimental investigation

Ultrasonic vibration (UV) assisted forming technology has been proved beneficial for lowering manufacturing issues and improving the forming qualifies of metallic products. However, the deformation behavior of ultrathin-walled microtube under the assistance of UV has not been clearly revealed due to the coupling effect of acoustic softening and size effect. In this research, UV assisted tensile test was performed on ultrathin superalloy sheets with different grain sizes to construct the constitutive model. The experimental results revealed that the grain size does not change the softening mechanism in ultrasonic-assisted microforming of ultrathin superalloy sheet. Whereas, the maximum acoustic softening value is shifted down with increasing grain size, indicating that the threshold of ultrasonic energy absorption is affected by grain size effect. A constitutive model considering the coupled effects of ultrasonic softening and crystal size was developed, and the logistic function is introduced into the acoustic term to describe the saturation of ultrasonic energy absorption. Based on the experimental and modeling results, the ultrasonic-assisted microdrawing process of the ultrathin-walled capillary was explored. The dimensional accuracy and surface appearance of the microformed capillary were significantly enhanced with increasing UV amplitude, and the ductility of capillaries after the UV assisted drawing is improved without loss of tensile strength under appropriate amplitude. Therefore, the ultrasonic-assisted microforming technology provides an efficient way for the coordinated regulation of forming quality and mechanical property of difficult-to-deform tubular micropart.