Influence of overhanging tool length and vibrator material on electromechanical impedance and amplitude prediction in ultrasonic spindle vibrator

This study presents the development of an ultrasonic transducer with a radius horn for an ultrasonic milling spindle (UMS) system. The ultrasonic transducer was intended to have a working frequency of approximately 30 kHz. Two different materials were considered in the study: stainless steel (SS 316L) and titanium alloy (Ti-6Al-4V). Titanium alloy gave a higher resonance frequency (33 kHz) than stainless steel (30 kHz) under the same preload compression stress. An electromechanical impedance simulation was carried out to predict the impedance resonance frequency for both materials, and the effect of the overhanging toolbar was investigated. According to the electromechanical impedance simulation, the overhanging toolbar length affected the resonance frequency, and the error was less than 3%. Harmonic analysis confirmed that the damping ratio helps determine the resonance amplitude. Therefore, damping ratios of 0.015–0.020 and 0.005–0.020 were selected for stainless steel and titanium alloy, respectively, with an error of less than 1.5%. Experimental machining was also performed to assess the feasibility of ultrasonic-assisted milling; the result was a lesser cutting force and better surface topography of Al 6061.