激光焊接瞬态小孔内部金属蒸汽动力学数值模拟研究

he dynamics of compressible vapor plume in a transient keyhole during laser welding of 304 stainless steel is studied by direct numerical simulation. The transient evolutions of keyhole and weld pool dynamics are solved by our recently developed keyhole welding model. The model rigorously considers the coupling effect of most important factors of laser welding, such as recoil pressure, surface tension, Marangoni effect, and multiple reflections Fresnel absorptions etc. A recently developed ambient pressure dependent recoil pressure model is also incorporated to include the effect of ambient pressure. The vapor plume dynamics inside the keyhole is assumed to be mainly driven by the recoil pressure and modelled by compressible Euler equations. The time dependent three-dimensional density, pressure, velocity and Mach number distributions of the plume inside a transient keyhole are solved. The results show that under the investigated welding conditions the vapor plume inside the keyhole is usually very unstable, and the distributions of density, pressure, velocity and Mach number are far from uniform and vary greatly with time. The vapor plume in the bottom and center part of the keyhole may run downward because of the high pressure zone produced in the center part of the keyhole. The vapor plume exit velocity continuously fluctuates and apparently presents the trend of gradually decreasing with time after the first rapid increased to a peak value, which is validated by our experiments. Moreover, the maximum velocity of the vapor plume in the keyhole can reach to be several hundred meters per second, and the oscillation frequency of the maximum velocity is about several kHz, which seems to be consistent with the existent experimental results.