Simulation of the multi-component process gas flow for the explanation of oxidation during laser cladding

Usually the process gas flow rates and the process gas types are not regarded as the primary process parameters of the laser cladding process. Herein it is shown, how the melt pool surface oxidation can be significantly reduced by the change of the carrier gas type, by a reduced carrier gas flow rate and by minor changes in the powder nozzle design. However, the absorptivity may decrease concurrently by up to 15%. A simulation model for the gas flow and the powder particle flow between the powder nozzle and the melt pool surface has been developed, which reveals the volume percentage of different gas types and so the quality of the shield gas atmosphere. Additionally, the powder particle distribution and the attenuation of the laser beam by the powder particles can be simulated. The simulation results are confirmed by experimental measurements of the powder particle density distribution in the working plane, by measurements of the oxygen volume percentage at the workpiece surface, by high-speed camera images of the melt pool surface and by absorptivity measurements, which show the effect of oxidation on the process.