Process Anatomy for High Aspect Ratio Micro-Hole Drilling with Short Micro-Second Pulses Using a CW Single-Mode Fiber

Abstract

The objective of this paper is to establish a detailed process anatomy of a micro-hole drilling process using a CW single-mode 300 W fiber laser with short micro-second pulses. For the drilling process with a one micro-second laser pulse, the process started with drastic evaporation and concluded with melt ejection approximately 150 micro-seconds later. It was concluded that two distinct hole drilling mechanisms occurred, one as adiabatic evaporation by the high power initial spike of the laser beam and one as melt ejection by the low power laser energy deposition. The drilling process time line was established based on the measurements by several in-process sensors, such as photodiodes, a high-speed camera, and a spectrometer. The theoretical modeling zoomed in the early stage of the process to investigate the hole formation which could not be observed experimentally. Both experimental and theoretical results were then compared to determine the laser-material interaction mechanisms among three media involved in the process: laser, material, and vapour/plasma. Finally, a series of temporal anatomy diagrams, denoted as process anatomy, were presented to describe the entire drilling process, including process temperature, laser energy deposition, hole formation, and material removal mechanisms.