Investigating the effect of gravity on long pulsed laser drilling

With the aim of improving the efficiency of laser drilling, an upward drilling method is proposed. In the experiment, a long pulsed laser beam was arranged to propagate upwards, in the opposite direction to gravity, and was used to drill hole at the bottom of an aluminum slab. A semi-infinite axisymmetric model of this system was also established. The analytical solution for the hole shape was derived by assuming that material, once it melted, was removed from hole with the aid of gravity. The calculation results agreed well with the experimental results. For further verification of the effects of gravity, the removed molten material and the hole shape for the downward (along the gravity direction) and the upward drilling cases were compared experimentally. In addition, the relationships between gravity, the inertia force, the surface tension and the viscosity were discussed. The results show that more molten material is expelled with the assistance of the gravity, and the laser energy is used more efficiently to melt the aluminum slab in the upward drilling.