Influence of incident angle on laser drilling

To drill sub-millimeter holes, laser percussion drilling has been a well-established industrial process for tens years. However, physical understanding is still quiet difficult because laser source can be instable with low pulse reproducibility, correlation between experimental parameters and hole morphology are not clearly identified. This paper deals with the study of hole morphology in function of peak power and incident angle. Holes are drilled with a millisecond laser source, their morphologic characteristics are essentially diameter, recast layer thickness, and depth. Results are based on a new and very fast hole analysis method (called DODO for Direct Observation of Drilled hOle). The influence on hole morphology of incident angle and peak power in a string of pulse are shown (drilled depth, diameter, recast layer thickness,…). Results reveals incident angle is not a determinant parameter in percussion drilling. The influence of peak power is fitted 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. With this drilling method, hole drilled has only one single recast layer at the end of the drilling, so hole cannot present some decohesion.