Dynamic characteristics of the growth of a vapour–gas channel during melting of metals by millisecond laser pulses

A simple method was developed for the determination of the lifetime and the rate of growth of a vapour–gas channel in spot welding by heating steel with laser pulses. The process was characterised by a high ratio of the depth to the diameter of a spot. Typical values of the lifetime and growth rate were determined for pulses with an optimised time profile. An increase in the depth of melting was due to an increase in the rate of growth of the vapour–gas channel, but the channel lifetime remained constant.