Development of a physical and mathematical model of gas flows in a triple coaxial nozzle

Abstract

The method of coaxial laser processing of powder materials is highly productive and takes place in a protective atmosphere. The shielding gas flows form the shape and structure of the cone of particles in such a way that with an increase in the axial flow of the shielding gas, a cylindrical cavity is formed inside the particle flow, in addition, the gas dynamically affects the bath of molten metal, and the deposited roller will be formed only at the edges of the flow, with a depression in the middle, which will lead to non-fusion of layers in the material. The external protective gas flow will compress the flow of particles and, if it exceeds a certain critical value, it can block it with a shift of the focus from the surfacing surface. In this regard, the flows of transporting and shielding gases must be supplied to the processing zone in a certain ratio to obtain deposited metal with a minimum number of defects. At the same time, it is necessary to ensure the supply of shielding gas with a flow rate that ensures the protection of the deposited metal until its crystallization. The purpose of this study is to determine the parameters of gas flows in a triple coaxial nozzle and the geometric parameters of the protected zone on the surface for the specified surfacing conditions. As a result of the calculation, the speed of flows in channels, streamlines, distribution of pressures and densities in the calculation area were determined. Based on the calculations, it is possible to draw the following conclusions that the flow velocities in the middle part of the flow area are equalized. In the central part, the flow speed reaches 12 m/s, towards the periphery, the speed decreases to 4 m/s. The size of the area protected by the gas flow on the surface is no more than one diameter of the outlet section from the axis of the nozzle, that is, the size of the protected area is equal to two diameters of the nozzle.