Study on Coupling Behavior of Keyhole Flow and Keyhole Wall in Deep Penetration Laser Welding

The hydrodynamic coupling behavior of gas-liquid interaction between the metal vapor in the keyhole and the keyhole wall during deep penetration laser welding determines the welding stability and affects the final welding quality.In this paper, stainless steel sheet metal and glass were clamped to make a dissimilar materials butt joint, and then the deep penetration laser welding of dissimilar materials was achieved.A high-speed camera was used to observe the characteristics of keyhole and the fluctuation of the keyhole wall from the glass side.The interaction behaviors between the vapor and the keyhole wall under different welding conditions were analyzed.The results showed that the effect of the vapor flow in the keyhole caused the keyhole wall to form a moving wave, which was accompanied by the formation of splash and liquid column when the moving wave crushed at the opening of the keyhole.During low speed welding process, the keyhole was deep, the keyhole vapor was fluctuating, and the keyhole wall was fluctuating frequently.The variation of laser beam defocusing distance effected the keyhole diameter and the laser energy distribution in the keyhole, and resulted in the change of the pressure and velocity of the vapor flow in the keyhole, thus changed the effect of the metal vapor on the hole wall in the keyhole.In deep penetration laser welding, the liquid metal on the rear keyhole wall was mainly moving upwards, which was driven by the gasification recoil pressure and vapor flow, and only a small part of the molten metal closing to the bottom of the keyhole was moving downwards.