Applying ultrasonic vibration during single-point and two-point incremental sheet forming

Abstract

Ultrasonic assisted (UA) deformation has been studied on a variety of materials in both fundamental tensile and compression tests as well as in relevant industrial processes. Reductions in flow stress are a common observation when applying UA during material plastic deformation. The objective of this work is to study the effects of ultrasonic energy on single-point (SPIF) and two-point (TPIF) incremental forming. A longitudinal ultrasonic vibration is applied to a hemispherical ISF tool at 20kHz oscillating frequency. A series of conical shapes were selected for UA-SPIF and a 45° conical shape backing die is selected for UA-TPIF. Generally, a positive correlation between oscillation amplitude and reduction in forming forces is observed in the investigated conditions. The force reduction in UA-TPIF is much more significant compared with UA-SPIF. It is hypothesized that UA-SPIF allows membrane vibration of the entire sheet, which lowers the effective ultrasonic energy input into the local plastic deformation region. In addition, UA-TPIF shows a local sheet thickness reduction in regions where ultrasonic oscillation is applied.