Experimental Study and Defect Control in Picosecond Laser Trepanning Drilling of Superalloy

Picosecond laser trepanning is a key technology for fabricating film cooling holes in aero-engine turbine blades, overcoming the limitations of conventional machining such as severe tool wear and thermal damage. However, optimizing this advanced process to achieve consistent, high-quality results remains a challenge. This study therefore systematically investigates the influence of key laser parameters (power, scanning speed, defocusing distance, and number of scans) on the geometric quality (diameter, taper, and roundness) of holes trepanned in GH4169 superalloy. The experimental results revealed that laser power and defocusing distance are the dominant factors controlling hole diameter and taper. Furthermore, a critical trade-off was identified concerning the number of scans: while more scans improved exit roundness, they also detrimentally increased entrance diameter and taper due to heat accumulation. Based on these findings, we propose a defect control strategy prioritizing a lower number of scans in the initial phase to effectively suppress molten material formation and preserve surface integrity. This work provides a valuable technological reference and theoretical foundation for the low-damage, high-reliability laser manufacturing of high-performance aerospace components.