THE SIMULATION OF FRONT KEYHOLE WALL DYNAMICS DURING LASER-WELDING

A physical model of keyhole support and propagation during high-transl ation-speed laser welding is described. A numerical code for the simul ation of the front keyhole wall behaviour is developed on the basis of a 'hydrodynamic' physical model assuming that: (i) only the front par t of the keyhole wall is exposed to the high-intensity laser beam; and (ii) recoil pressure exceeds surface tension and propagation of the k eyhole wall inside the sample is due to melt expulsion similar to that in laser drilling. The front keyhole wall profile, distribution of ab sorbed 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 a bsolute value of the keyhole wall velocity component parallel to the t ranslation velocity vector can be higher than, smaller than or equal t o the beam translation speed. When the component of the keyhole veloci ty vector parallel to the sample surface was higher than the beam tran slation speed, the formation of the humps on the keyhole wall was obse rved numerically.