High-power CW CO 2 laser beam channeled penetration into liquid

Hydrodynamical phenomena in the process of laser welding and cutting

“…The flow in these streams manifests as non-stationary 3D whirls in the bottom of the KH with average velocities of the order of 1 m s 21 . 20 The periodic rising of the melt pool upper level as a result of the melt transfer caused by moving shelves, humps and squeezing away process induces capillary oscillations in the bulk. The frequency of this oscillation equals that of emergent processes like shelf, hump and squeezing away.…”

“…The velocities of liquid phase movement in these streams are in the range of 10 2 -10 3 cm s 21 . 20 The physical mechanisms responsible for emergence of high Reynolds number flow in the melt pool can be attributed to the thermocapillary effect, transport of the liquid surface layer by tangential impulse of condensing vapour flow, viscous drag of the tangentially moving vapour and injection of a submerged stream arising from the front wall of the KH with moving shelf/hump into the melt pool. The driving force for stream injection arises from impulsive vapour pressure bursts caused by evaporating microdroplets.…”

“…The driving force for stream injection arises from impulsive vapour pressure bursts caused by evaporating microdroplets. 8,20 Yet another hydrodynamic phenomenon in laser material processing stems from splashing from the melt pool. It may occur in the process of KH formation in a fixed specimen where the rate of laser beam power buildup is too high and does not match the velocity of radial expansion of the melt zone, i.e.…”