Stability analysis and chatter suppression of ultrasonic elliptical vibration milling of Ti-6Al-4V alloy

Ti-6Al-4V alloy is a typical aircraft material to be difficult machined. Ultrasonic elliptical vibration-assisted milling has been proved to greatly enhance machining performance. In ultrasonic elliptical vibration milling (UEVM), the cutting edge moves in 3D space, reducing extrusion friction between the flank and machined surface, and playing an important role in high precision-efficient manufacturing of difficult-to-cut materials. This paper focused on the stability analysis and chatter suppression of ultrasonic elliptical vibration milling of Ti-6Al-4V alloy. There are separated and unseparated types of ultrasonic elliptical vibration milling systems, which stability is analyzed in this study by simulating their tool tip motion paths. The essence of the tip and workpiece at high-frequency separation is revealed through analysis of cutter tooth path in UEVM. Next, the coordinate method is used to set up the window function to facilitate the derivation of true instantaneous chip thickness. The dynamic model of UEVM is established to study the system stability and plot its stability prediction lobes diagrams. The effect of machining parameters on the system stability is assessed and discussed in detail. The prediction results show that the stability region and axial depth of cut grow with the increase of feed rate per tooth and decrease of ultrasonic frequency. Among the six groups of ultrasonic amplitude parameters studied, the optimal system’s stability corresponds to the ultrasonic amplitudes of 5 and 3 μm in the x - and y -directions, respectively. Finally, stability tests of UEVM are performed, which results well match the numerical simulation predictions. This implies that the proposed window function is adequate, the theoretical model is valid, and the predicted stability curve is feasible and reliable.