Laser micro through-hole modification on the surface of narrow cavity parts without back wall damage based on axial shaping Bessel beam

A beam regulation method is employed to address the issue of back wall damage caused by laser processing of structures such as micro through-holes on the surface of narrow cavity parts. This approach reduces back-wall damage by rapidly truncating the laser energy along the transmission path. An analytical method is used to shape the Bessel beam, followed by smoothing and oscillation optimization via apodization and amplitude modulation to obtain a Bessel beam capable of rapid energy truncation. The ablation capability and controllability of the Bessel beam in the axial ablation direction on nickel-based alloys are verified through grooving experiments. To protect the back wall, a modification strategy is proposed that utilizes a rapidly truncated Bessel beam to remove residual material from prefabricated micro-holes, resulting in complete micro through-holes without back wall damage. The effects of defocusing extent and depth of focus on the micro through-hole modification are investigated. Experimental studies demonstrate that combining Bessel beams with 1 mm and 2.5 mm depths of focus reduces modification time by 22 min when compared to a single depth-of-focus Bessel beam. Micro through-hole modification on a 0.5 mm narrow cavity part is successfully achieved using this method without causing damage to the back wall.