Hydrodynamical model of melt component stratification during scanning-laser-beam interaction with heterogeneous materials

Abstract

A physical model of formation of stratified structures of components in a stiffening melt after the action of a penetrating laser beam on the heterogeneous system is considered. The model explains the formation of layers by centrifugal "running' or "tightening' of microparticles in size about 104-102cm of an impurity (either heavier, or easier in relation to the basic material). This centrifugal effect should be shown in vortex melt flows, with speeds in the range of several cm/s, generated by hydrodynamic instabilities of the certain nature. In the case of continuous scanning of a CW beam along the surface of a material, there can be generated non-stationary regular three-dimensional vortex melt flows explained by injection of flooded melt jets from a front wall keyhole (KH). After solidification of the heterogeneous melt, behind of traveling KH the strip-looking layers of an insoluble impurity are observed in the direction of beam scanning velocity. Our experimental data do not contradict to this model. In the case of cylindrical-symmetric layer melt, surrounding the KH in the absence of scanning of the laser beam, the vortex flows arise due to capillary collapse ofthe KH. After deenergizing the laser and solidification ofthe melt, periodic layers of the insoluble impurity are fixed which look like curved "disks" located transverse to the keyhole axis.

Efficiency of laser beam utilization in gas laser cutting of materials

“…where ∆ m is the width of the material melted layer that is average for the plate thickness, ν m is the velocity of melt removal [4]. Relationship (4) represents the matching between the sample motion and the melt layer removal.…”

“…Relationship (4) represents the matching between the sample motion and the melt layer removal. On the other hand, from the commonly accepted model of the steady-state melting wave we have [4,11]:…”

“…Formula (5) allows for matching between the sample motion and heating of the material layer of ∆ m thickness, attended by melting. From ( 4) and ( 5) follows the relationship of the cutting speed and the melt surface heating temperature [4,11]:…”

“…With an increase in the cutting speed, the temperature T s goes higher and at the highest possible speed it approaches the boiling point (T s = T B ) [4].…”

“…In this technology, the processes of interaction between scanning beam radiation and condensed media play an important part. The physics of this interaction is very complicated and involves energy balance, conservation of mass and impulse, dynamics of heating with melt formation, and their complex dynamic interrelation [3][4][5][6][7][8][9]. The efficiency of laser beam utilization is one of the crucial issues under examination.…”