Weld pool flows during initial stages of keyhole formation in laser welding

Abstract

Weld pool transport phenomena during the transition from conduction-mode laser spot welding to keyhole laser spot welding of titanium were studied by numerical simulation. A range of laser powers were simulated and temperature dependent evaporation recoil pressure and cooling were applied as boundary conditions on the weld pool surface. Simulation results predicted a complex time-varying flow pattern during weld pool development. The surface-normal flow at the weld pool centre oscillated between upwards and downwards during the simulation time due to interaction of competing effects of evaporation recoil and surface tension pressures and laser heating and evaporation cooling. The results show that the laser weld pool flow dynamics play a key role during the transition from conduction-mode laser welding to keyhole welding.

Effect of metal vaporization behavior on keyhole-mode surface morphology of selective laser melted composites using different protective atmospheres

“…3c). Moreover, the evaporation metal gas is entirely covered near the keyhole center from the transient temperature field, thus leading to the occurrence of strong ablation and the resultant recoil pressure forced on the molten pool [24]. At the iteration time t = 6 × 10 −3 s, the keyhole is completely the same as that obtained at t = 5.4 × 10 −3 s, indicating that a stable and desired keyhole is reasonably obtained after 5.4 ms (Fig.…”

“…3a). This phenomenon can be analyzed that the absorbed energy is preferentially used to heat and melt the metal powder in the upper region of the powder layer and subsequently overcome the melting and evaporation latent heat barrier of the material [24]. In this processing condition, the molten pool depth is considerably controlled by the conduction of heat in the underlying solid material.…”

Microstructure and Mechanical Properties of Ti5553 Butt Welds Performed by LBW under Conduction Regime

“…In fact, LBW-CR is being nowadays investigated for different purposes, such as to confirm the simulation results. Thus, simulation studies were performed to understand the weld pool flow patterns of titanium, showing that laser weld pool flow dynamics play a key role during the transition from conduction mode to keyhole [24]. A model is presented by Du et al [25] for flow simulation of full penetration laser beam welding of titanium alloy, concluding that the molten pool becomes shorter and wider under the conduction regime, as a consequence of the Marangoni effect.…”

A Review on Melt‐Pool Characteristics in Laser Welding of Metals

“…Cho et al [88] simulated the fluid flow in the melt-pool during the transition from conduction laser spot welding to keyhole laser spot welding and showed an upward and downward oscillation in the fluid flow in the center of the melt-pool in the direction of normal to the surface. ey attributed this oscillation to interaction of competing pressures, including recoil pressure and surface tension pressure.…”