High-efficiency and stable laser transmission for laser and electrochemical machining

Abstract

Laser and electrochemical machining (LECM) has been increasingly adopted to improve the efficiency and surface quality of micromachining. The coupling and high-efficiency transmission of laser in electrolyte are critical to the implementation of LECM, which were rarely studied in previous research. In this study, the geometric and simulation model of laser coupling and transmission within the electrolyte jet has been established for laser and shaped tube electrochemical machining (Laser-STEM). The critical coupling condition and transmission efficiency of laser beam was investigated theoretically. Influences of laser coupling errors on the laser transmission efficiency and laser power intensity distribution at the exit of hybrid tool electrode were explored. Results indicated that the angular offset had the greatest impact on laser transmission efficiency, while the longitudinal offset impact the least, which were accordance with the experimental results. The thresholds of laser power intensity and the frequency of the laser-induced electrolyte breakdown were measured. The thresholds for laser-induced breakdown in NaNO3 solution were higher than that in NaCl solution. The laser power intensity threshold of laser-induced electrolyte breakdown increased with the increase of focal length, and the frequency of smaller than 4.5 could be obtained with the laser power density ranging from 2.35e9 to 1.06e10 W/cm2 at the focal spot. The distribution trended to more uniform at the exit with the increase of hybrid tool electrode length. A laser coupling efficiency of larger than 81.2 % has been achieved by utilizing the hybrid tool electrode with NA of 0.534 and acceptance angle of 32.3°. Finally, experiments with a designed raster-shaped workpiece were conducted to verify the feasibility of laser transmission in large depth in the Laser-STEM process. The high aspect-ratio small holes with a depth of 50 mm, and a diameter of 1.3 mm have been processed by using Laser-STEM.