Effect of process parameters on gas shield of coaxial powder feeder nozzles

In order to improve the shielding effect of gas flow field in laser direct manufacturing, the shielding gas flow field of coaxial powder feeder nozzles was studied by means of smoke flow visualization technology.The influence of gas velocity from nozzle, distance between parts and nozzle exit,moving velocity of nozzle and crosswind velocity on shielding gas field was investigated systematically. The results show that with the increase of gas velocity from nozzle,shielding effect increases at first and then gets worse; with the increase of velocity of crosswind and nozzle,the axis of shielding field and nozzle get apart; when the velocity of crosswind surpasses 50% of velocity of gas from nozzle, shielding field fails to protect molten pool totally at the place 10mm below the nozzle.The information can be used to select appropriate nozzle flow parameters.