Monitoring and analysis of millisecond laser drilling process and performance with and without longitudinal magnetic assistance and/or assist gas

Abstract

A systematic investigation was reported for observing and analyzing the process and performance of millisecond laser drilling with and without magnetic assistance and/or assist gas using a self-developed real-time monitoring system based on high-speed photography. The systematic and corresponding comparisons between the effects of longitudinal magnetic assistance and co-axial assist gas for millisecond laser drilling of both blind holes and through holes using high-speed photography were first reported. Using a direct comparable visual method based on comparable observations using high-speed camera, the effects of the co-axial assist gas and/or the longitudinal magnetic assistance on millisecond laser drilling process, drilling efficiency and drilling quality were systematically analyzed by correspondingly comparing and correlating the real-time observations with the measurements for laser drilled specimens, including the characterizations and analyses for material removal, plume expansion and dispersion, specimen spatters, hole geometry/morphology, hole sidewall recast layer and micro hardness performance. It was shown that the metal vapor and plasma induced by a millisecond laser mixed with each other as a hybrid plume. The co-axial assist gas flow was observed to be much more effective than the longitudinal magnetic field for promoting plume dispersion and enhancing drilling efficiency during the processes of blind-hole drilling and through-hole drilling. When using the assistance of a co-axial argon flow together with a longitudinal magnetic field, the blowing and cooling effects of assist gas were dominant during the laser drilling process, and the longitudinal magnetic assistance further vertically squeezed and horizontally stretched the plasma, greatly reducing the shielding effect of laser-induced plume for effectively increasing laser drilling efficiency and quality.