Effects of water temperature on femtosecond laser layered-ring trepanning in superalloy with water-based assistance

Abstract

The effects of the water temperature on the hole quality in water-assisted femtosecond laser layered-ring trepanning on superalloys were studied. The effects of the laser pulse repetition rate on the hole entrance/exit diameters, taper angle, and hole sidewall morphology and roughness at different water temperatures were compared and analyzed. The results show that at a water temperature of 70 ℃, the diameter of the hole entrance decreased, while that of the hole exit increased, compared with those at 20 ℃. Both the hole entrance and exit diameters decreased at 2 ℃. The hole taper angle was the largest when the water temperature was 20 ℃, followed by 2 ℃, and was the smallest at 70 ℃. When the laser pulse repetition rate was 300 kHz, the hole taper angle at 70 ℃ decreased by 43.6 % compared with that at 20 ℃. As the water temperature increased, the roughness of each part of the hole sidewall decreased. When the pulse repetition rate was 200 kHz, the quality of the hole sidewall improved under water-based assistance conditions, while the hole quality improved at a water temperature of 70 ℃, compared with drilling in air. As the water temperature increased, the water was more likely to evaporate, resulting in an increase in the amount of bubbles. As more bubbles moved upward, the water flow increased. The debris and materials generated by laser drilling were more effectively removed, thereby improving the drilling efficiency. The use of a higher water temperature was beneficial to obtain holes with smaller taper angles and a higher sidewall quality. The experimental results provide a reference for optimizing water-assisted femtosecond laser drilling. This methodology can be applied to the aerospace and semiconductor industries.