# Altering the Supply of Shielding Gases to Fabricate Distinct Geometry in GMA Additive Manufacturing  
[PERSON]  
1 Mechanical Engineering Department, Georgia Southern University, Statesboro, GA 30458, USA; [EMAIL_ADDRESS]  
[PERSON]  
1 Mechanical Engineering Department, Georgia Southern University, Statesboro, GA 30458, USA; [EMAIL_ADDRESS]  
[PERSON]  
2 Mechanical Engineering Department, University of North Dakota, Grand Forks, ND 58202, USA; [EMAIL_ADDRESS]  
[PERSON]  
3 CSIRO Manufacturing, Lindfield, NSW 2070, Australia; [EMAIL_ADDRESS]  
[PERSON]  
4 Energy and Transportation Science Division, Oak Ridge National Laboratory, Knoxville, TN 37932, USA; [EMAIL_ADDRESS] (A.N. ); [EMAIL_ADDRESS] (M.W.N.) [PERSON]  
5 Manufacturing Science Division, Oak Ridge National Laboratory, Knoxville, TN 37932, USA5 Manufacturing Science Division  
In traditional arc welding, shielding gases are primarily used for the prevention of atmospheric contamination and oxidation during the metal transfer and solidification processes. The welding community has produced its own recommended practices for selecting and using shielding gas. The type of shielding gas selected affects the metal transfer and the subsequent weld bead shape [5] and mechanical properties [6]. In the arc welding and WAAM processes, the shielding gas also affects the heat transfer and fluid flow of the molten pool. The melt pool absorbs surface active elements from the shielding gases, causing the size of the weld pool to change. This can have a significant impact on the resulting microstructure and mechanical behavior of the built component, as well as on the dimensions of the beads and, therefore, the dimensional accuracy of the deposits [7]. The dimensional accuracy of large-scale WAAM parts, in comparison to the computer-aided design (CAD) model, is generally poor compared to those produced by other AM processes. Oversized parts are built to compensate for this lower-dimensional accuracy, but this increases the post-processing (machining) time, thus reducing the overall productivity and energy efficiency of the process. Clearly, a change in tool path programming is necessary to achieve dimensionally accurate parts via WAAM. Therefore, the primary goal of this research is to understand the effect of shielding gases on the dimensional accuracy of a large-scale AM process, which is critical for the economic feasibility of the WAAM process. A ternary shielding gas blend, He-Ar-CO\({}_{2}\) (90-7.5-2.5%), and a binary blend, Ar-CO\({}_{2}\) (90-10%), were selected for this study. Helium was selected because it has a high  
Figure 1: Wire arc manufactured propeller demonstrator at Oak Ridge National Lab Manufacturing Demonstration Facility. The propeller was printed in 20 h and weighed around 60 kg. thermal conductivity, higher ionization potential, and lower density. The addition of helium generally increases weld pool fluidity by absorbing more heat compared to other shielding gases. In addition, the ternary blend has also been suggested by industrial users for arc welding of martensitic stainless steel. The binary blend of argon and carbon dioxide is commercially used in gas metal arc welding (GMAW) applications. A recent study has shown that adding 5-10% CO\({}_{2}\) is ideal for the WAAM processing of low-carbon steels [8] ([PERSON] et al., 2020). In this research, the use of the ternary mixture is hypothesized to increase the fluidity of the weld pool region, resulting in a broader bead width. Thus, the size of the bead width can be altered by changing the shielding gases without adjusting the other AM parameters. Such an approach may be beneficial for the built part because it could achieve a more dimensionally accurate structure. Previous studies have shown that altering the shielding gas can improve part quality and reduce manufacturing costs [9; 10]. [PERSON] et al. [11] studied the effects of different shielding gases in aluminum GMAW and achieved improvements in weld metal porosity and the weld penetration profile.