Material removal and surface generation in longitudinal-torsional ultrasonic assisted milling

Ultrasonic Machining (UM) is extensively used in processing of difficult to cut materials due to its superior performance. However, the mechanics of this process is still not fully understood when superimposed on other machining operations. In this paper, Longitudinal-Torsional Ultrasonic Assisted Milling (LTUAM) is introduced for machining of a high strength titanium alloy Ti-6Al-4V. The separation geometrical characteristics between the tool and workpiece are studied analytically. Moreover, the texturing generation mechanism of LTUAM is analyzed through a theoretical model. The proposed method considers the influence of 3D tool topography, which can accurately simulate the ultrasonic surface topography. Related experiments of the generated cutting force and the surface topography were conducted to investigate the machining characteristics. The results showed that compared with Conventional Milling (CM), a noticeable decrease of the cutting force was observed in LTUAM. This can be explained from the perspective of tool workpiece contact rate model. Micro dimpled surface textures were successfully fabricated on Ti-Al6-4V using LTUAM technique. The surface test results indicated that the surface micro-hardness was enhanced between 6.34% and 13.22% compared with CM. This research provides guidance for applications of ultrasonic machining to textured surfaces.