A review of ultrasonic machining of brittle materials: Process parameter optimization and crack formation mechanisms

Ultrasonic machining is a non-conventional machining technique widely used for the precise processing of brittle materials such as glass and ceramics. Method employs high-frequency vibrations (typically above 20 kHz) combined with abrasive slurry to achieve controlled material removal. Despite its advantages, such as low thermal damage and independence from electrical conductivity, ultrasonic machining often suffers from low material removal rate and crack formation at the inlet and outlet regions during micro-hole fabrication. Recent studies have reported that optimization of process parameters can significantly improve machining performance. Recent empirical findings indicate that properly selected vibration amplitude and abrasive size can increase material removal rate by up to 25–40%, while reducing edge chipping and crack formation by approximately 20–30%. Additionally, the use of rotary ultrasonic machining has been shown to further enhance surface quality and reduce tool wear compared to conventional vertical ultrasonic machining. This study presents a comprehensive literature-based analysis of ultrasonic machining applied to micro-hole fabrication in brittle materials, focusing on crack formation mechanisms and the influence of key process parameters such as frequency, amplitude, abrasive grain size, and slurry concentration. The findings highlight that optimized parameter combinations can effectively minimize micro-cracks while improving surface integrity and machining efficiency. The outcomes of this review provide quantitative insights into process optimization and identify critical research gaps, guiding future studies toward high-precision and damage-free micro-machining of brittle materials. This review synthesizes and critically evaluates optimized process parameter ranges reported in the literature for the efficient fabrication of micro-holes, with particular emphasis on minimizing crack formation. Rather than proposing a new optimization framework, this study consolidates and analyzes previously reported parameter configurations and their influence on crack formation and machining performance in a holistic approach.