ABSTRACT
Laser beam welding is a thermal joining technique whereby the joining of two parts is established during the solidification of a common melt pool. The required thermal energy stems from the electromagnetic energy of the laser beam focused onto the surface of the workpiece. It is transformed into heat within a thin volume layer, the thickness of which corresponds to the penetration depth of the electromagnetic radiation. Since for metals, this amounts to only fractions of the wavelength, the thermal energy released can be characterized as a surface heat source. As in any other laser treatment process, however, the detailed mechanisms and phenomena involved in the interaction of laser beam and workpiece depend on the balance between the energy fluxes coupled into the interaction zone and transported away from there, essentially by heat dissipation. With increasing intensity, the irradiated material may experience several phase changes from solid to liquid and again to vaporization. As a result of the ablating material’s recoil pressure on the melt pool, the interaction zone itself may also change from a generally plane surface to eventually capillary penetration into the workpiece-the so-called keyhole. According to the characteristic features occurring at low (below 105 W cm−2) or high intensity (several 106 W cm−2), the welding process is classified as heat conduction welding or deep penetration welding.
