A TRANSPORT THEORETICAL-MODEL OF THE KEYHOLE PLASMA IN PENETRATION LASER-WELDING

In laser welding with high laser intensities a hole is formed in the m aterial, the so-called keyhole. In this keyhole a plasma is detected, which is characterized by high charge densities and high pressure as w ell as being influenced by the boundary of the keyhole. We describe th e transport of the laser power into the material by the plasma for a C O2 laser and iron. We set up a system of stationary transport equation s for the ions, electrons and non-excited neutrals, which contain conv ective transport and heat flux. The boundary conditions take into acco unt the evaporation of neutral atoms from the hot keyhole surface and the transition from the quasineutral presheath plasma to the sheath pl asma. With the incident laser power as input parameter we obtain the r adial variation of the hydrodynamic variables and quantities like the degree of ionization, the electron temperature and the fraction of abs orbed laser power.