Ceramics and other hard-and-brittle materials are very effectively processed by longitudinal-torsional coupled rotary ultrasonic machining (LTC-RUM), which cutting force evolution and the effects of processing parameters on the material removal mechanism need to be optimized. This study introduced the LTC-RUM cutting force model of zirconia ceramics based on the brittle material removal mechanism. Firstly, the kinematic analysis of a single abrasive grain was performed, with further consideration of the material removal volume, the effective contact time, and the impact force per one ultrasonic vibration cycle. Then, the longitudinal-torsional coupled vibration of the core tool was analyzed from the wave energy conversion standpoint. The analytical model was finalized and experimentally verified by LTC-RUM tests, which results closely correlated with the ones predicted via the proposed model. With the spindle speed, feed rate, and ultrasonic power variation, the maximum discrepancies between the predicted and experimental cutting forces are 15.51, 13.24, and 8.3%, respectively. The results obtained are considered instrumental in predicting the effects of processing parameters on the cutting force during LTC-RUM of ceramics and their further optimization.

The high performance of parts is determined by the microstructure of the machined surface to some extent. Different processing methods have been used to construct different microstructures on machined surfaces; the effective improvement of the serviceability of parts has been the focus of research in the field of precision and ultra-precision machining. In the presented work, a microscratch was formed on the machined surface in ultrasonic assisted machining, and the surface microstructure of high-performance aluminum alloy processed by single-excitation rotational longitudinal–torsional coupled ultrasonic vibration (LTCUV) milling was investigated. First, the motion paths model of the cutting edge in the LTCUV milling were established; then, the single-excitation LTCUV milling system has been set up, and the acoustic performance of the LTCUV system was examined. The surface microstructure of aluminum alloy was processed by different machining techniques, and the effect of processing parameters on the surface microstructure and performance were investigated by the orthogonal design of experiment (DOE). The surface roughness was found to be proportional to the ultrasonic cutting speed and feeding rate. The surface roughness was mainly controlled by the ultrasonic amplitude, and the optimal surface quality corresponded to the ultrasonic amplitude of 4 μm. The cutting speed contributes greatly to the surface roughness. The water contact angle of surfaces obtained by ultrasonic processing was larger than that of surfaces achieved by the conventional processing, while the surface water contact angle was negatively related to the ultrasonic amplitude. Once the rotation speed exceeded a critical level, the ultrasonic amplitude exerted a negligible effect on the surface water contact angle. The cutting speed contributes the most to the water contact angle. The friction coefficients of surfaces treated by ultrasonic processing were lower than those obtained by conventional processing at constant processing parameters, while the friction coefficient was minimized at the ultrasonic amplitude of 4 μm. In the case of grease lubrication friction, the surface wear decreased with the ultrasonic amplitude, indicating the improved wear resistance of the processed surfaces. Similarly, the ultrasonic amplitude has the highest contribution rate to friction and wear.

Ultrasonic-assisted electrolytic in-process dressing (UA-ELID) grinding is a promising technology that uses a metal-bonded diamond grinding wheel to achieve a mirror surface finish on hard and brittle materials. In this paper, the UA-ELID grinding was applied to nanocomposite ceramic for investigating the cavitation effect on the processing performance. Firstly, the ultrasonic cavitation theory was utilized to define the cavitation threshold, collapse of cavitation bubbles, and variation of their radii. Next, the online monitoring system was designed to observe the ultrasonic cavitation under different ultrasonic amplitude for the actual UA-ELID grinding test. A strong effect of ultrasonic cavitation on the grinding wheel surface and the formed oxide film was experimentally proved. Besides, under the action of ultrasonic vibration, the dressing effect of the grinding wheel was improved, and the sharpness of grain increased by 43.2%, and the grain distribution was dramatically changed with the increase of ultrasonic amplitude. Compared with the conventional ELID (C-ELID) grinding, the average protrusion height increased by 14.2%, while the average grain spacing dropped by 21.2%. The UA-ELID grinding reduced the workpiece surface roughness R_z and R_a by 54.2% and 46.5%, respectively, and increased the surface residual compressive stress by 44.5%. The surface morphology observation revealed a change in the material removal mechanism and improvement of the surface quality by ultrasonic cavitation effect. These findings are considered instrumental in theoretical and experimental substantiation of the optimal UA-ELID grinding parameters for the processing of nanocomposite ceramics.

This study aimed to explore the evolution of surface properties of nanocomposite ceramics during ultrasonic vibration-assisted electrolytic in-process dressing (UVA-ELID) grinding. First, the trajectory of the grain was analyzed, and the motion was simulated using MATLAB to demonstrate the mechanism of UVA-ELID grinding. The critical grinding depth was also calculated under the effect of ultrasonic vibration. Then, the conventional ELID (C-ELID) and UVA-ELID grinding were compared. The surface properties, including surface residual stress, surface microstructure, surface roughness, and surface morphology, were used to evaluate the effectiveness and feasibility of UVA-ELID grinding. Whether it was conventional C-ELID or UVA-ELID grinding, the residual compressive stress was introduced into the machined surface, while the former was lower than the latter. The microstructure of the UVA-ELID grinding was evenly distributed, and the ductility removal occurred during material removal. The surface roughness of Ra and Rz was reduced by 14.5% and 20.6%, respectively, during the UVA-ELID grinding. The surface morphology was dramatically changed with the help of ultrasonic vibration. In a word, for nanocomposite ceramic, the UVA-ELID grinding can significantly improve surface performance and achieve a better machining effect.