Stress superposition effect in ultrasonic drawing of titanium wires: An experimental study

Benefits of ultrasonic vibration have been identified in metal forming and other manufacturing processes, yet the underlying mechanism has not yet been fully understood. In this paper, influences of ultrasonic vibration on the titanium wire drawing process were investigated in terms of ultrasonic amplitude, drawing speed, and position of the die. Longitudinal vibrations were superimposed upon the die via a tailor-made ultrasonic vibrator, whose dynamic performances were predicted by finite element analysis (FEA) and examined utilizing specific instruments. A single-pass ultrasonic wire drawing platform was established to measure the forming forces under various drawing conditions, which were subsequently compared with numerical simulation results. Surface morphologies of the drawn wires were inspected by scanning electron microscope (SEM). Results show that both increased ultrasonic amplitude and lowered drawing speed contribute to decreasing the drawing forces, but the efficiency is furthered influenced by location of the die. At the half-wavelength position, a significant drawing force reduction of 66.8% (from 22.5 N to 7.45 N) was observed with the ultrasonic amplitude and drawing speed of 9μm and 100 mm/s, respectively. At the quarter-wavelength position, however, the corresponding percentage reduction is only 21%. The phenomenon could be explained by the elastic stretching oscillation of the wire based on the stress superposition hypothesis.