Influence of Metal Transfer Behavior Under Ar And CO2 Shielding Gases On Geometry And Surface Roughness of Single And Multilayer Structures In GMAW-Based Wire Arc Additive Manufacturing of Mild Steel

Wire arc additive manufacturing (WAAM) is advantageous for fabricating large-scale metallic components, however, a high geometric accuracy as that of other AM techniques cannot be achieved because of the deposition process with a large layer. This study focuses on the WAAM process based on gas metal arc welding (GMAW). To clarify the influence of shielding gas used to protect a molten metal during fabrication on the geometric accuracy of the built part obtained via the GMAW-based WAAM process, the influence of the metal transfer behavior on the geometry and surface roughness of the fabricated structures was investigated via visualization using a high-speed camera when single and multilayer depositions were performed under different heat inputs and gases. However, when using Ar gas, the heat flux from an arc to the workpiece is relatively low, limiting the depth of the molten pool during welding. The effect of its characteristics on the stair steps that are inevitably produced on the side face of the multilayer structure in the WAAM process was verified, and for a heat input of 1.17 kJ/cm under Ar gas, a higher geometric accuracy of the multilayer structure was obtained without interlayer cooling. The short circuit between the metal droplet and the fabricated surface, where the molten pool is insufficiently formed, resulted in a hump formation. Further, the metal transfer under Ar gas reduced the surface irregularities on the fabricated structure.