Search

Wire arc additive manufacturing (WAAM) is the process by which large, metallic structures are built, layer-by-layer, using a welding arc to melt wire feedstock. In this process, the proper selection of the shielding gas plays a vital role in the achievement of structurally acceptable part geometries and quality surface finishes. In this study, the authors used either a ternary mix (He, Ar and CO2) or a binary mix (Ar and CO2) of shielding gases to deposit wall geometries using an open loop-controlled WAAM system developed at Oak Ridge National Laboratory's Manufacturing Demonstration Facility. The binary blend produced a wider and shorter geometry, while the ternary blend resulted in a narrower build that was more equivalent to the CAD geometry. The data indicated that the binary blend provided a higher oxygen concentration in the weld as compared to that of the ternary blend. The results imply that the arc characteristics and heat input had a significantly higher impact on the weld penetration than the surface tension effect of surface active elements. This was further verified by developing and applying a high-fidelity computational fluid dynamics (CFD) model of the thermophysical properties of gas mixtures. The results from the model showed that, while the influence of increased oxygen concentration on the surface tension for the binary blend led to a deeper penetration, the ternary blend gave rise to heat flux to the workpiece. [ABSTRACT FROM AUTHOR]

Bead-on-plate experiments were carried out, and the weld-bead size and shape were compared and discussed. The welding droplet parameters were measured by a high-speed camera. A computation fluid dynamics (CFD) model utilizing VOF (volume of fluid) method, incorporating the experimental droplet parameters has been developed to understand the weld pool dynamics and subsequent weld pool geometry. From the experimental results, a narrower and deeper penetration was observed with hot-wire while wider and shallow penetration was observed with cold wire gas tungsten arc welding (GTAW). The developed model has been applied to predict and analyze the mechanism for narrower and deeper penetration. A modified relationship has been established for droplet detachment in hot wire GTAW. [ABSTRACT FROM AUTHOR]