Acoustic Streaming-Assisted Underwater Laser Micromachining Process

Abstract A critical problem in the underwater laser micromachining process is the optical disturbance caused by gas bubbles in water, where the laser beam quality and cut quality are significantly deteriorated. This paper introduces an acoustic streaming-assisted underwater laser ablation technique, where an ultrasonic transducer is positioned parallel to the workpiece surface. This configuration generates a cross-streaming water flow that effectively removes laser-induced debris and bubbles during the ablation in water. A pure titanium sheet was drilled by a nanosecond pulse laser subjected to acoustic streaming in a water chamber. A glass window for confining water and separating it from ambient air was recommended to minimize the optical disturbance caused by water waves. By using the proposed laser micro-drilling technique, a clean through-hole, small hole taper angle of as low as 6.8 deg, and minimal heat-affected zone (HAZ) were achievable compared to laser micro-drilling in air and in water without the assistance of acoustic streaming. The effects of laser power and drilling duration on hole dimensions and HAZ indicated that the hole entrance diameter increased from 270 µm at 10 W to 410 µm at 30 W, while the HAZ width expanded up to 128 µm only. Statistical analysis using ANOVA showed that laser power had a significant effect on the hole entrance and HAZ, whereas drilling duration had a minor impact. The proposed technique can thereby be an effective method for high-precision microscale machining with reduced thermal damage.