Study on the mechanism of ultrasonic-assisted water confined laser micromachining of silicon

The ultrasonic-assisted water confined laser micromachining is a novel micromachining method. This paper reports the experimental studies of ultrasonic power and water layer thickness on the laser (1064 nm nanosecond pulse laser) micromachining of silicon. Besides, this reports a systematic discussion on the influence of the acoustic streaming and bubbles (induced by laser) dynamic change on the machining process. The acoustic streaming and flow pattern under different ultrasonic power application and different water layer thickness using Particle Image Velocimetry (PIV). A finite element (FE) heat transfer model was employed to gain a better understanding of the effect of the acoustic streaming velocity on the temperature field change in laser processing. The bubbles (induced by laser) dynamic behavior is observed by the high-speed camera. The results showed that the ultrasonic-assisted laser ablation can yield much higher the material removal rate than laser cutting in water without ultrasonic-assisted. Besides, the increase in the ultrasonic power helps to improve the etching efficiency but is not apparent. When the water layer thickness is 1 mm, the cutting effect is significantly different from the laser ablation in the other three water layers. Through the PIV images and simulate results, it has been found that the influence of acoustic streaming on heat transfer in laser processing is small. Through high-speed camera imaging observations, the dynamic change of bubbles is an essential mechanism for the enhanced material removal rate and affect the machining performance in this study. This study helps understand the mechanism of ultrasonic-assisted water confined laser micromachining better and promoting this technique potential application in the micromachining of hard brittle materials.