Ti-6Al-4V alloy is extensively used in aerospace, biomedical and automotive industries for processing the precise and ultra-precision parts because of its excellent material properties. However, the ultra-precision processing of Ti-6Al-4V alloy has always been a challenge. In this paper, a series of experimental investigations was performed to study the ultra-precision processing feasibility of Ti-6Al-4V alloy with different ultrasonic vibration-assisted cutting modes. The surface defect, surface roughness and chip formation under conventional cutting (CC), ultrasonic linear vibration assisted cutting (ULVC) and ultrasonic elliptical vibration-assisted cutting (UEVC) of Ti-6Al-4V alloy were analyzed. The experimental results revealed that, in the CC process, many surface defects like adhered particles, chip fragments and grooves appeared, and the long continuous ribbon chips were produced. In the ULVC process, the side flow appeared, which greatly deteriorated the surface integrity. Furthermore, the long helical chips were obtained. In contrast, an almost flawless-machined surface was obtained in the UEVC process, and its roughness value was 39.2 nm, which was decreased nearly 31% than the roughness value in CC process and 40% in ULVC process. Moreover, the shorter, helical and controllable chips were obtained. Experimental results indicated the UEVC was applicable for ultra-precision cutting of Ti-6Al-4V alloy.

The micro-groove structure on the planar surface has been widely used in the tribology field for improving the lubrication performance, thereby reducing the friction coefficient and wear. However, in the conventional cutting (CC) process, the high-quality, high-precision machining of the micro-groove on titanium alloy has always been a challenge, because considerable problems including poor surface integrity and a high level of the material swelling and springback remain unresolved. In this study, the ultrasonic elliptical vibration assisted cutting (UEVC) technology was employed, which aimed to minimize the level of the material swelling and springback and improve the machining quality. A series of comparative investigations on the surface defect, surface roughness, and material swelling and springback under the CC and UEVC processes were performed. The experimental results certified that the material swelling and springback significantly reduced and the surface integrity obviously improved in the UEVC process in comparison to that in the CC process. Furthermore, for all the predetermined depths of the cut, when the TSR (the ratio of the nominal cutting speed to the peak horizontal vibration speed) was equal to one of twenty four or one of forty eight, the accuracy of the machined micro-groove depth, width and the profile radius reached satisfactorily to 98%, and the roughness values were approximately 0.1 μm. The experimental results demonstrate that the UEVC technology is a feasible method for the high-quality and high-precision processing of the micro-groove on Ti-6Al-4V alloy.

In this paper, a novel single-driven ultrasonic elliptical vibration cutting (SDUEVC) device with a succinct structure and a simple assembly is proposed and investigated. A tailored horn with a tilted-slot structure was employed in the designed SDUEVC device. Also, the elliptical trajectory formation mechanism of the designed SDUEVC device was described by using the theory of mechanical vibration. Furthermore, the finite element method (FEM) was used to optimize the tilted-slot structure parameters and there are four parameters selected as the optimization factors. The results indicated that the proposed SDUEVC device can generate larger vertical amplitude than previous SDUEVC devices, which provides an important and positive effect for the cutting performance of the proposed SDUEVC device. According to the optimized results, a prototype SDUEVC device was fabricated and its vibration characteristic was tested. When the excitation signal voltage was 500 V_p-p, the test results indicated that the amplitudes in the axial and vertical directions were 8.7 μm and 6.8 μm, respectively. Furthermore, an elliptical trajectory was generated at the cutting tool tip. Finally, the proposed SDUEVC device was used to fabricate microdimple patterns as the initial application to confirm the feasibility of the proposed SDUEVC device.