Experimental study on surface residual stress of titanium alloy curved thin-walled parts by ultrasonic longitudinal-torsional composite milling

The production of thin-walled titanium alloy curved surfaces is of great significance to aerospace manufacturing industry. The magnitude and distribution of residual stress are one of the important factors affecting the surface integrity of the workpiece. In order to obtain larger surface residual compressive stress, improve the surface integrity of the workpiece, and realize the fatigue-resistant manufacturing, the ultrasonic longitudinal-torsional composite milling method was proposed. Orthogonal and single-factor experiments were carried out on titanium alloy curved thin-walled parts, and the differences of cutting force, cutting temperature, and residual stress between conventional milling and ultrasonic longitudinal-torsional composite milling were compared and analyzed, and the influence of different process parameters on the surface residual stress of titanium alloy thin-walled parts was explored. Compared with conventional milling, the surface residual stress values of ultrasonic longitudinal-torsional composite milling workpiece were negative and significantly increased, with the maximum increase rate of 54.88%.The cutting force was greatly reduced, and Fx and Fy decreased by 31.6% and 45.33%, respectively. The instantaneous cutting temperature was also greatly reduced, the maximum reduction of which is 17.53%. With the increase of ultrasonic amplitude and feed per tooth, the surface residual compressive stress increases gradually but decreases with the increase of spindle speed and curvature. The experimental results show that ultrasonic longitudinal-torsional composite milling is a reliable method for machining titanium alloy curved thin-walled parts, which can obtain larger residual compressive stress and improve the machined surface integrity.