Long-pulse fibre laser micro-hole drilling of nickel superalloy

Abstract

The laser drilling process represents state-of-the-art technology for producing components with micro-holes across various engineering sectors, from hybrid laminar flow control in aerospace to electrodes in hydrogen systems. Various types of lasers are used to create micro-holes, ranging from long-pulse fibre lasers (multi-mode or single-mode) to short and ultra-short pulse lasers. This research focuses on understanding the characteristics of micro-hole (<100 µm) drilling in 1 mm thick nickel superalloy using a long pulse (millisecond) multi-mode quasi-continuous-wave fibre laser with a fibre core diameter of 50 µm and a focus spot size of 35 µm. The effects of various process parameters on drilling performance have been evaluated, and a high-speed camera has been used to gain a detailed understanding of the process. The results of this study have been compared with our previous work on high-power multi-mode laser drilling (fibre diameter of 100 µm and focus spot size of 75 µm) and single-mode fibre laser drilling (fibre diameter of 15 µm and focus spot size of ~15 µm). Despite significant variations in focus spot beam sizes across different laser setups, the optimised minimum hole diameters for millisecond pulse laser drilling of 1-2 mm thick nickel alloy remained consistently in the range of ~70-80 µm, suggesting that heat conduction and melting phenomena play a critical role in determining hole size.