Effect Of Gas-powder Flow On The Molten Pool Morphology For Coaxial Powder-feed Laser Cladding

As a new surface modification technology, laser cladding can be applied toimprove the surface corrosion and wear resistance of the parts, and repair theworn-out parts (remanufacturing) and produce metal parts directly, which has beenwidely used in various industries. Gas and powder work as key roles in lasercladding and directly affect the size and shape of the molten pool, so it isnecessary to study the aspects of gas-powder flow.According to the power equilibrium theory in the quasi-steady-state, anequilibrium equation which describes the free surface on molten pool of lasercladding was studied. The gas-powder flow and gravity of molten pool liquid on freesurface were studied, which was expressed in mathematical equilibrium equation.And the curvature K of molten pool free surface was obtained, which could confirmthat the free surface of molten pool is not a simple circular surface.The effect of the transporting gas flow on powder feed rate and the divergentangle of the powder flow in the exit of coaxial nozzle，and the effect of the shieldinggas on the molten depth below the substrate surface were studied in this article. Theappropriate range of transporting gas flow and shielding gas flow was obtained:8~12L/min,7~12L/min.The two-dimensional numerical model of gas-powder flow of laser claddingwas built using FLUENT-acommercial fluid software. The simulation results showthat the velocity of gas-powder flow entering the molten pool increases with theincrease of shielding gas flow, transporting gas flow and the velocity of powder flow.The impact on the molten pool increases with the decrease of the curvature K ofmolten pool free surface, which affects the shape of cladding bead. Semiconductorlasers and robot was used in the experiments, the results show that the upper part ofthe cross-sectional outline of cladding bead is flatter with the increase of theshielding gas flow and transporting gas flow in the process parameters, whichreflects that the free surface curvature of molten pool is smaller. The experimentalresults were in good agreement with the theoretical analysis of molten pool freesurface and the numerical simulation of gas-powder flow.