New experimental approach to study laser matter interaction during drilling in percussion regime

Abstract

Laser drilling is a well-established process in aerospace industry. However quality and geometry of holes do not get under control in an absolute way. Moreover, drilling understanding is complicated due to the number of parameters and physical phenomena. Laser and matter have some own parameters which are not constant with temperature, and so could not be fitted. In this paper, we describe the mechanism of laser-matter interaction for drilling with single and multi-pulse with a new method (called DODO for Direct Observation of Drilled hOle). We show the existence of a threshold between two drilling shapes called conical and round shape. With geometric optic approach, a simple model estimate the drilling depth corresponding to a drilling with round bottom shape. We show the influence of the peak power in a string of pulse on hole morphology (profile, diameter and quality). The influence of peak power fit in the string pulse to eliminate the recast layer cracking. It comes from a solidification of a melt layer on a previous recast layer. To eliminate it from the hole it is essential to melt the previous recast layer with higher peak power pulse than the previous one.