S-Polarization Laser Beam Welding

Abstract

The availability of high power lasers with average power levels above 5 kW and high beam quality triggered a number of industrial applications of lasers. Especially the process of deep penetration welding made the use of lasers attractive in applications where low distortion and small heat affected zones are required. In deep penetration welding a channel, called keyhole, supported by the pressure of evaporating material is formed by the laser beam, which allows the radiation of the laser a direct access to deep layers of the material. This is in contrast to conventional welding, where the heat either has to diffuse from the surface to the bulk material by heat conduction or the heat must be allowed to reach deeper layers by pro-viding a direct access using a preformed chamfer which has to be closed by filler material. By moving the laser beam relative to the material, the keyhole is driven parallel to the surface. The material molten at the front of the keyhole flows around the keyhole and resolidifies in its wake. The diameter of the keyhole and the thickness of the fluid layer necessary to support the flow around the keyhole determines the minimum width of the molten area and the width of the heat affected zone and hence the minimum energy per unit length of the seam if deep penetration laser welding is used.