Investigation of the WAAM processes features based on an indirect arc between two non-consumable electrodes

Abstract

The wire and arc additive manufacturing (WAAM) method based on an indirect arc between two non-consumable tungsten electrodes in confined space has been proposed and preliminarily investigated, which is applicable in vacuum or sub-atmosphere ambient conditions. Visual inspection results showed that the stable burning arc kept continuously melting the metallic wire. Because there is no current flowing through the droplets and molten pool, the important process feature of low heat input was revealed. A cubic boron nitride (CBN) ceramic nozzle is used to force the arc and to produce droplets pass through it for additional constriction and trajectory regulation. The constricted-shielding gas and arc plasma offer fine protection and additional heating for the melted droplets during the whole process. The arc length increased as the gas flow rate rose from 4 L/min to 10 L/min. The arc shapes became dispersed when the gas flow rate exceeded 10 L/min. The arc shapes and droplets transfer process can be improved by the ceramic nozzle. Both of the forming characteristics and metallurgical bonding strength can be dramatically improved. The geometrical dimensions of each layer can be effectively regulated through adjusting wire feed and depositing speed.