Evaporation in deep penetration welding with laser radiation

In deep penetration welding most of the molten material does not cross the keyhole as vapour but has to be accelerated around it. The driving force for this acceleration is assumed to be given by the ablation pressure of evaporating material. The required evaporation rate and the power needed for the evaporation process itself are calculated. It is shown that although the pressure gradients in the melt increase drastically with the processing velocity, the power needed for evaporation is negligible in a wide range of parameters.