CHARACTERISTIC MELT POOL HYDRODYNAMIC BEHAVIORS FOR CW ND-YAG DEEP PENETRATION LASER WELDING

摘要

We discuss the characteristic melt flows inside the melt pool that are observed when we vary the welding speed from very low welding speed (a few m/min) to very high one (30 m/min). At low welding speed, the keyhole is quite vertical embedded inside a large pool that fluctuates due to friction effects induced by the quite vertical ejected plume. At high welding speeds, laser interaction is only localized on the keyhole front whose inclination increases with the welding speed. Induced melt flow then dominates and can generate the humping regime, with severe undercuts. For intermediate welding speeds, it is the interaction of the vapor plume with the melt pool that controls its stability. It is concluded that the interaction of the vapor plume, which is emitted with a variable dynamic pressure and direction, perpendicularly from the inclined keyhole front, has an essential role for melt pool stability and its dynamics in laser welding.