Product Code: ICAL06_M1203

New Experimental Approach to Study Laser Matter Interaction during Drilling in Percussion Regime
Authors:
Schneider Matthieu, GERAILP/LALP; Arcueil France
Laurent Berthe, GERAILP/LALP; Arcueil France
Maryse Muller, CNRS/GERAILP; Arcueil France
Remy Fabbro, GERAILP/LALP; Arcueil France
Presented at ICALEO 2006

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, physical phenomena and material properties.In this paper, we describe the mechanism of laser-matter interaction during drilling process. The laser source from Trumpf is characterized by a statistical study. Output parameters are very stable and the laser beam is a constant top-hat intensity distribution at the focal plane. Each matter state (liquid and vapor) behaviour is described from visualisation performed with an ultra fast camera (100.000 fps) from Photonlines. Parameters to master the drilling of reproducible holes are shown. The liquid metal ejection, which is controlled by peak power density, determines the hole quality and the thickness of recast layers.The assistant gas plays two main roles. Firstly, it protects optics and secondly it cleans the output hole at the end of the drilling. Moreover, during the drilling, the assistant gas is opposite to the expansion of the metallic vapor. Results show clearly that: -the two jets are supersonic and have stationary shock waves, -assistant gas does not penetrate inside the hole, -the vapor expansion is stopped by a surface shock wave. This vapor confinement by the assistant gas could explain why the target surface can be remelted. It also modifies the geometry and the quality of the hole. The drilling velocity is also measured and compared with the model of Semak and Matsunawa for several target thickness. The drilling velocity decreases with the target thickness increasing. The influence of laser parameters like laser intensity and multi-reflexion confirms this limitation. In conclusion, whole of results allows a new comprehensive approach of the process and the determination of dominant parameters.