Product Code: ICAL09_1702

Laser Drilling in Percussion Regime: Study of the Scale Time of the Breakthrough
Authors:
Laurent Berthe, Laboratoire pour l'Application des lasers de Puissance (UPR CNRS 1578); Arcueil France
Maryse Muller, Pimm/Cnrs; Paris France
Matthieu Schneider, Pimm/Cnrs; Paris France
Mariette Nivard, Pimm/Cnrs; Paris France
Presented at ICALEO 2009

The laser drilling in percussion regime consists in irradiating a target with a laser in the power density range of 10 MW/cm2 and pulse duration in ms range . The beam and the target are static. The material is heated, melted and vaporized. The drilling is produced by the removal of the liquid layer using recoil pressure from the irradiated zone. Even, this process is used for the drilling of cooling systems in aeronautics since many years, fundamentals phenomena are not well-known. Recent works have demonstrated some specific phenomena at the interface liquid/vapor, the effect of assistance gas and fine relations between hole morphology and laser parameters. We propose in this paper a study of the break through. This phase of the drilling is complex. The melt part is ejected by the rear face of the hole by two types of different gas. At the beginning, hole diameter is smaller than the laser one. The high vapor pressure in the hole ejects the melt material by the rear face. The melt layer is still heated by the laser. During the second step of the break through, the assistant gas penetrates inside the breaking through hole and then accelerated the cooling of the melt layer. because of the coefficients of friction, the melt material is still ejected through the rear face during the solidification. This new study is based on direct observations of the rear surface of a target using a high speed camera (100 000 Frames/s). Main phenomenas are evidenced and time scales of the breakthrough are measured. Theses results are determinant to estimate the response time of a breakthrough detection system.