Stability of the melt in a vapour – gas channel during melting of metals by pulsed laser radiation.

An analysis was made of the experimental data on the stability of a molten bath when millisecond pulses from a free-running laser with a variable time profile interacted with steel. At certain critical radiation power densities, the molten bath began to lose its stability and liquid metal particles were ejected under the action of pulses with different profiles. It was established that the necessary condition for retention of the stability of the molten bath during the formation and growth of a vapour – gas channel was the appearance of a fairly large primary volume of the melt (buffer volume). This could be ensured by broadening the leading edge of the radiation pulses. Optimisation of the radiation parameters made it possible to increase a depth of the moving melting front amounting to 5.8 mm when the energy per pulse was 34.0 J. The critical radiation power density then exceeded by a factor of 6 the corresponding density for melting without the formation of a vapour – gas channel.