Analytical model for the depth progress of percussion drilling with ultrashort laser pulses

Abstract

A simplified analytical model is presented that predicts the depth progress during and the final hole depth obtained by laser percussion drilling in metals with ultrashort laser pulses. The model is based on the assumption that drilled microholes exhibit a conical shape and that the absorbed fluence linearly increases with the depth of the hole. The depth progress is calculated recursively based on the depth changes induced by the successive pulses. The experimental validation confirms the model and its assumptions for percussion drilling in stainless steel with picosecond pulses and different pulse energies.

High-quality percussion drilling with ultrashort laser pulses

“…5. As expected from the model [18] presented in Sect. 4, the diameter of the entrances remains almost constant with increasing number of pulses.…”

“…Both studies indicate that the fluence has a significant influence on the quality of the microhole's exit. The fluence reaching the far end of the hole changes with the evolving geometry of the hole being drilled [18]. As known from experiments, the same happens with the quality of the holes.…”

“…An important step in this direction was to understand and describe the heat accumulation that occurs during machining with ultrashort laser pulses [10][11][12][13] and its consequences on the drilling process [14,15]. When heat accumulation effects and particle-ignited plasmas can be avoided, it is possible to estimate the final depth of percussion-drilled microholes with an analytical model [16,17] and the temporal evolution of the drilling depth can be predicted [18]. In the latter case, the use of optical coherence tomography (OCT) proved to be a promising diagnostic method to measure the drilling progress online.…”

“…The quality-reducing effects that can occur during laser drilling are manifold and the impact of these effects include shape deviations, striations, burrs, side channels, and the formation of multiple holes. Although the studies published in [16] and [18] deal with the production of high-quality microholes, the classification of high-quality microholes primarily only refers to the exclusion of thermal damage and excessive melting due to heat accumulation. The quality of the microhole's edge on the side where the laser beam exits and its dependence on processing parameters was not investigated in these studies and is now addressed in the present work.…”

Review on Experimental and Theoretical Investigations of Ultra-Short Pulsed Laser Ablation of Metals with Burst Pulses

“…A large number of laser pulses and a sufficiently high pulse energy is typically required to produce blind and through holes with high aspect ratios of 1:10 or more. The reason lies in the nature of the drilling process, where, in general, the irradiated area increases with drilling depth and pulse number, and, hence, the fluence within the bore holes decreases over time [ 74 , 154 , 155 ]. Principally, this requirement contradicts the splitting of pulse energy during burst processing to allow for an improvement in laser drilling processes in terms of drilling time and, hence, efficiency.…”