Optical diagnostics and optimization of the gas-powder flow in the nozzles for laser cladding

摘要

The results of investigation of gas and gas-powder flows in various cladding nozzles are presented and discussed. Schlieren-imaging, high-speed imaging and laser Doppler anemometry were used for optical diagnostics of the flows. It is demonstrated that diameter of the outlet in removable cyclone cap has significant impact on the powder flow pattern in an off-axis nozzle. It provides a convenient way to optimize focusing of the powder flow. It is found that stable vortices that appear near the surface of the substrate significantly reduce efficiency of powder material use when off-axis nozzle is applied. It is demonstrated that excessive shielding gas flow rate in four-stream and coaxial nozzles may lead to defocusing of gas-powder flows. A possibility to increase the efficiency of powder use in various laser cladding nozzles through modification of their design as well as shielding and carrier gases flow rates is discussed.