Process applicability and hole wall microstructure evolution mechanism of femtosecond laser spiral drilling

Abstract

In this work, a 1.5 mm thick GH3044 nickel-based superalloy is processed by femtosecond laser to obtain a micro-hole for the fuel nozzle of an aerospace engine with a large thrust-to-weight ratio. To address the issue of sidewall adhesion during micro-hole machining, a spiral drilling method implemented with a rotating wedge scanning module is used. Combined with a two-step drilling strategy, it achieves flexible removal of adhesion while ensuring machining efficiency and further improving the quality of drilling. The effect of different drilling strategies on the sidewall roughness of micro-holes is investigated. After process optimization, the roughness of the the micro-hole sidewalls is reduced to below Rq 0.4 μm, which is approximately 8% compared to the traditional one-step drilling strategy. Based on the EBSD analysis results, it is observed that the microstructure of the micro-hole sidewalls remains largely unchanged regardless of the drilling strategy employed. The analysis of the micro-hole sidewalls shows the presence of periodic microstructures. When aiming for low roughness, the geometric characteristics of these periodic microstructures can be adjusted by manipulating the laser's single pulse energy. These experimental findings present a new perspective for optimizing the femtosecond laser drilling process and provide theoretical support for future enhancements in the actual fuel injection effect.