レーザー誘起プラズママイクロマシニングにおけるキャビテーションダイナミクスが異なる液体中での性能に及ぼす影響

This study investigates the influence of cavitation bubble dynamics on the performance of laser-induced plasma micromachining in three commonly used liquid environments: deionized water, saline solution, and ethanol. A combination of high-speed imaging experiments and numerical simulations is employed to explore how different liquid properties and focal positions affect bubble behavior and jet formation near the workpiece surface. Cavitation bubble oscillations are first captured in free-field conditions to characterize fundamental dynamics. These parameters are then used in OpenFOAM-based simulations to model bubble evolution on solid surfaces. The results reveal that saline solution produces the smallest lateral bubble expansion and the highest downward jet velocity, leading to minimal peripheral erosion and enhanced vertical material removal. Groove machining experiments in titanium alloy validate these findings and highlight the role of both plasma and cavitation in shaping machining outcomes. It is found that while plasma dominates vertical material removal, bubble jets assist in debris removal and contribute to groove formation. The results further indicate that an excessively large focal distance, despite enhancing jet velocity, reduces plasma-material coupling and weakens overall machining efficiency. This work provides valuable insights into optimizing laser-induced plasma micromachining by controlling cavitation behavior and focal positioning to balance precision and processing performance.