# Altering the Supply of Shielding Gases to Fabricate Distinct Geometry in GMA Additive Manufacturing
## 3 Conclusions  
This study demonstrated that the fabrication of distinct geometries through the WAAM process is possible by altering only the shielding gas (in this case, by using a binary and a ternary blend). The present investigation lays the groundwork for geometry control in the wire arc additive process by altering the shielding gas, while keeping other process parameters constant. These results can be useful for obtaining dimensionally accurate structures. The key findings from this study are:  
* The selection of the shielding gas plays an important role in the dimensional accuracy of WAAM-fabricated parts. The binary blend of argon and carbon dioxide produced a wider bead, while the ternary blend formed a narrower bead shape with a deeper  
Figure 18: Velocity comparison for (**a**) a 500 ppm oxygen concentration with low heat flux, representing the binary blend and (**b**) a 420 ppm oxygen concentration with high heat flux, representing the ternary blend.  
penetration depth, when a surface tension transfer process with the selected arc welding parameters was used to fabricate a wall.
* Variations in geometry could be achieved by altering the shielding gas without altering the other AM parameters.
* There was a difference in heat transfer and thermal efficiency when the shielding gas was changed without changing other AM parameters. By considering the thermophysical properties of the two gas mixtures and the arc lengths, it was concluded that the arc radius at the workpiece was lower for the ternary-blend shield gas, leading to a higher heat flux.
* The concentration of the surface active element oxygen was higher with the binary blend. A computational model was used to demonstrate that the influence of the oxygen concentration on the Marangoni circulation led to an increase in weld penetration depth. However, it was found that the increased heat flux for the ternary blend dominated the influence of the surface active element.  
Future developments and modifications of the numerical model through the evaluation of the metal transfer process and shielding gases study will allow qualitative improvements in the design of parts for WAAM.  
Conceptualization, B.S. and A.N.; methodology, B.S., A.N., M.W.N., S.R.; software, N.P., A.B.M.; validation, B.S., A.B.M.; formal analysis, B.S., A.B.M.; investigation, B.S. resources, M.W.N.; data curation, N.P.; writing--Original draft B.S.; writing--review and editing, all authors.; visualization, S.R., B.S.; supervision, B.S., A.N., M.W.N.; project administration, M.W.N., A.N.; funding acquisition, M.W.N., A.N. and B.S. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors would like to thank [PERSON], [PERSON], [PERSON], and [PERSON] for providing support during different the experiments. The authors would also like to acknowledge the support from their collaborating partners, Lincoln Electric and Wolf Robotics, on this project, and access to the wire arc additive manufacturing setup at the Manufacturing Demonstration Facility in Oak Ridge National Laboratory. This material is based on work supported by the U.S. Department of Energy, Office of Science, Office of Advanced Manufacturing Office under contract number DE-AC05-00 OR22725. This work was supported in part by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists (WDTS) under the Visiting Faculty Program (VFP).  
The authors declare no conflict of interest.