Abstract
Evaporation characteristics in CO2 laser welding stainless steel was experimentally analyzed at power densities in a range from 5×104 to 107 W/cm2 with M2 of 1.4 and 5.6. Welding mode transits from a thermal conduction to a deep penetration type at a critical power density around 4-5×105 W/cm2. The penetration depth tends to increase with decreasing M2 with accompanying decreased evaporation loss when the power density at the work surface is the same. The latent heat of evaporation is negligible small, at most around 1% of laser power. In the thermal conduction welding, where the power density is less than 4-5×105 W/cm2, the evaporation rate per unit area was found to be equivalent to that of the deep penetration welding, indicating that the recoil force of the evaporation is at least as high as that of the keyhole welding, providing a shallow hemispherical depression by the recoil force in the molten pool. The evaporation rate in the deep penetration welding decreases with increasing aspect ratio of the weld bead due to the condensation of the vapor at the side wall of the keyhole.
