Beam Absorption Mechanism In Laser Welding

Abstract

Mechanism of laser beam absorption was analyzed in key hole welding of thin plate and deep penetration welding of thick plate on the basis of the two-dimensional cavity model where beam is absorbed by cavity wall and ionized metal vapor. The beam absorptivity of the cavity wall A and the absorption coefficient of the plasma u are approximately 50 % and 1- 1.5 cm^-1, respectively. In key hole welding of thin plate, laser beam is absorbed predominantly by the liquid cavity wall and the cavity shape is self-controlled so as to absorb the energy required for bead formation. In deep penetration welding of thick plate, laser power is absorbed mainly by plasma where the self-controlling is less effective, and hence excess energy absorbed at low welding speeds is w'sted to widen the bead with little increase in penetration depth. In vacuum of 10^-3-10^-4 torr, u decreases down to approximately 0.5 cm^-1, providing large penetration depth.