The simulation of front keyhole wall dynamics during laser welding

A physical model of keyhole support and propagation during high-translation-speed laser welding is described. A numerical code for the simulation of the front keyhole wall behaviour is developed on the basis of a `hydrodynamic' physical model assuming that: (i) only the front part of the keyhole wall is exposed to the high-intensity laser beam; and (ii) recoil pressure exceeds surface tension and propagation of the keyhole wall inside the sample is due to melt expulsion similar to that in laser drilling. The front keyhole wall profile, distribution of absorbed laser intensity and phase velocity of the solid/liquid (liquid/vapour) boundary are calculated for various processing parameters. The calculations show that, depending on the processing conditions, the absolute value of the keyhole wall velocity component parallel to the translation velocity vector can be higher than, smaller than or equal to the beam translation speed. When the component of the keyhole velocity vector parallel to the sample surface was higher than the beam translation speed, the formation of the humps on the keyhole wall was observed numerically.