Hydrodynamic analysis of laser drilling process

Laser drilling is a complex process that involves material removal through both vaporisation and hydrodynamic melt ejection. The process is further complicated when an assist gas is incorporated, which is often the case under most practical drilling conditions. It is the intend of this paper to investigate these effects through both theoretical analysis and experiments. The theoretical analysis covers thermal conduction in the solid, vaporisation, vaporisation-induced recoil pressure, melt ejection, convection due to the melt flow as well as the attendant effects of using an O2 assist gas, which include the effect of assist gas pressure on the melt surface, the forced convection cooling and the additional energy generated due to the oxidation of the melt surface by the O2. The effects of the absorbed laser intensity on the melt surface temperature, melt ejection velocity and drilling velocity were studied for both cases of laser drilling with and without O2 assist gas and compared to experimental results obtained for EN3 low carbon steel.