Optimization of control variables in rotary ultrasonic machining of alumina ceramic for reduced edge chipping and enhanced surface finish

Owing to its outstanding and superior properties, alumina is a well-documented advanced ceramic to realize numerous manufacturing and medical applications. However, machining alumina using traditional techniques is difficult, time-consuming, and sometimes impossible due to its high hardness, brittleness, and low electrical and thermal conductivity. Rotary Ultrasonic Machining (RUM) is among the most frequently reported methods for drilling holes in ceramics. However, extensive edge chipping is also noticeable in RUM both at the entrance and at the exit of the hole if correct machining variables are not considered. This research, therefore, focuses on experimentally exploring the significance of RUM control variables, notably: spindle speed, feed rate, ultrasonic amplitude, and ultrasonic frequency on edge chipping and surface roughness. The experiments are planned through the response surface methodology, which is dependent on a central composite rotatable design. The distinctive selection of RUM parameters that mitigate edge chipping may produce unfavorable outcomes for the surface finish. This assumption underlines the necessity of multi-objective optimization to ensure competitive RUM efficacy for hole drilling in alumina. A gray relational analysis paired with a principal component analysis (GRA–PCA) framework is embraced to identify optimal drilling variables for RUM. The procedure of optimizing multiple quality attributes (edge chipping and surface roughness) to elevate the quality of hole drilling in alumina ceramic using the GRA–PCA method is illustrated. According to this study, the feed, along with speed, amplitude, and frequency, has the biggest impact on RUM efficacy. The findings of this investigation reveal that the minimal surface roughness ( R a = 0.29 µm and R t = 1.19 µm) and lowest area of edge chipping at the hole entrance and exit (0.29 mm 2 and 1.36 mm 2 , respectively) can be achieved using the following parameters: speed −6000 rpm, feed rate −0.5 mm/min, amplitude −35 µm, and frequency −23 kHz.