Chatter suppression and stability analysis of rotary ultrasonic milling titanium alloy thin-walled workpiece

Titanium alloy and its thin-walled structures are widely used in the aerospace field. Aiming at the processing chatter and difficult-to-machine problem of titanium alloy thin-walled workpieces, rotary ultrasonic milling technology (RUM) is employed to restrict machining vibration in this paper. Firstly, the titanium alloy web with low stiffness is equivalent to a mass-spring-damping system with three degrees of freedom for describing its dynamic characteristics. Then, a novel stability analysis method is proposed for RUM thin-walled workpiece (RUM-tww) through defining an ultrasonic function angle. Furthermore, RUM-tww stability lobe diagrams (SLDs) are achieved based on the semi-discrete method (SDM). The simulation results show that the milling stability of titanium alloy webs is improved effectively under the effect of ultrasonic vibration energy. Compared with conventional milling thin-walled workpiece (CM-tww), the stability region of RUM-tww is increased by 80.32% within the spindle speed from 1000r/min to 5000r/min. Finally, milling experiments are carried out to verify the validity and rationality of SLDs via analyzing chatter marks, cutter marks and flatness on the machined surface. The experimental results are in good agreement with the theoretical prediction.