Altering the Supply of Shielding Gases to Fabricate Distinct Geometry in GMA Additive Manufacturing

Abstract

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.

Effects of Flowrate of Additional Shielding Gas on the Properties of Welded Seam by Twin-wire GMAW Welding for Duplex Stainless Steel

“…As the gas flowrate was 16 L/min, the over-protection phenomenon of the gas jet occurred on the welded seam. Under an excessively large flowrate of additional shielding gas, the seam had a grooved morphology with a lower middle part and higher sides, which indicated that the impact force of the jet exceeds the actual requirement of the liquid pool significantly [28]. The reason for the formation was that the molten pool becomes depressed under the excessive impact force acting on the molten pool.…”

General expressions for heat distribution, pressure, and current density in argon welding arcs

“…There are different deterministic mathematical models of the arc reported in the literature. These were used with different goals: some assess the role of the shielding gas composition [5], [6], the impact that metal vapor plays on the arc characteristics [7], [8], and some models quantify the effect of the arc current and length on the arc-substrate interactions or determine the impact of the tip angle of the cathode and filler metal [9]- [11], among other studies. The complexity of the reported models also show marked differences; some models include multiphase modeling [12], other solve the non-equilibrium nature of the species present in the arc [13], and a few simulate transient arcs [14].…”