Effects of Acoustic Softening and Hardening in High-Frequency Vibration-Assisted Punching of Aluminum

Punching operations contain high shear stress gradients which can exhibit adiabatic strain rate effects in certain materials at higher speeds due to a localized reduction of thermal lattice vibrations. Ultrasonic forming is known to soften material undergoing plastic deformation by direct application of lattice vibrations. Punching speed and ultrasonic vibration amplitude effects are investigated in sheets of 1100-O aluminum. Ultrasonic vibration more than negated adiabatic strain rate effects at high speeds with reductions in punching force of up to 30%. At lower speeds, a competing effect from acoustoplastic hardening resulted in a smaller effect on punching force, but increased ductility.