# Altering the Supply of Shielding Gases to Fabricate Distinct Geometry in GMA Additive Manufacturing
## 2 Results and Discussion
### Mathematical Model
The height of the bead from the top surface of the base metal decreased, and the bead radius increased as the heat flux increased, as shown in Figure 9. \begin{table}
\begin{tabular}{c c} \hline \hline
**Property** & **Value** \\ \hline Surface tension of pure metal at melting temperature (N m\({}^{-1}\)) & 1.943 \\ Viscosity (kg m\({}^{-1}\) s\({}^{-1}\)) & 0.006 \\ Specific heat (J kg\({}^{-1}\) K\({}^{-1}\)) & 460 \\ Thermal conductivity (W m\({}^{-1}\) K\({}^{-1}\)) & 22 \\ Liquidus temperature (K) & 1811 \\ Solidus temperature (K) & 1670 \\ Latent heat of fusion (J kg\({}^{-1}\)) & 2.45 \(\times\) 10\({}^{5}\) \\ Reference temperature (K) & 1670 \\ Contact angle (degree) & 90 \\ Saturation pressure (N m\({}^{-2}\)) & 1.01 \(\times\) 10\({}^{5}\) \\ Saturation temperature (K) & 2843 \\ Latent heat of vaporization (J kg\({}^{-1}\)) & 6.34 \(\times\) 10\({}^{6}\) \\ Specific heat ratio & 1.41 \\ Vapor specific heat (J kg\({}^{-1}\) K\({}^{-1}\)) & 460 \\ Universal gas constant (J mol\({}^{-1}\) K\({}^{-1}\)) & 8.314 \\ Initial drop temperature (K) & 2000 \\ Surface excess at saturation (mol m\({}^{-1}\)) & 2.03 \(\times\) 10\({}^{-8}\) \\ Negative of temperature coefficient of surface tension of a & 4.3 \(\times\) 10\({}^{-4}\) \\ pure Metal (N m\({}^{-1}\) K\({}^{-1}\)) & 0.0138 \\ Constant related to entropy of segregation & 0.0138 \\ Standard heat of adsorption (J mol\({}^{-1}\)) & 1.463 \(\times\) 10\({}^{5}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Data related to surface tension used in the numerical simulation. **Case 2: Same input heat flux with different surface tensions. **  
An identical heat flux value was used for these simulations, while different surface tension coefficient values were used. Oxygen concentrations of 310 ppm, 420 ppm, and 500 ppm were used to calculate the surface tension, according to Equations (1) and (2). Figure 10 shows the surface tension and surface tension coefficient with respect to the temperature for the three oxygen concentration values. The figure shows that as the temperature increased, the surface tension coefficient became negative (Figure 10). However, increasing the oxygen concentration increased the maximum temperature for which the surface tension coefficient remained positive from 2400 to \(\sim\)2600 K.  
Figure 9: Melt pool dimension using different heat fluxes: q (**a**), 3q (**b**), and 6q (**c**). Figure 10: Surface tension relationship with respect to oxygen concentration (**a**) surface tension and (**b**) surface tension coefficient. The results show that, under a higher concentration of oxygen, deeper penetration was achieved as compared to lower oxygen concentrations (Figure 11). Moreover, a high oxygen concentration was correlated with lower surface tension. The product of surface tension and the surface curvature balances the arc pressure and droplet pressure [29], so increasing the surface tension is expected to give a lower surface curvature. This trend is apparent in Figure 11: the bead height is slightly lower in Figure 11a, for which the surface tension is highest, than in Figure 11c, for which the surface tension is lowest. A higher oxygen concentration gives a higher surface tension coefficient, and the coefficient remains positive, up to a higher temperature. This means that the Marangoni flow is inward, towards a higher temperature, which promotes an inward and downward flow pattern, leading to a deeper weld pool, as also seen in Figure 10. These results are consistent with the results obtained by [PERSON] et al. [30] using sulfur as a surface active element in spot GMAW. Figure 12 shows the simulation results of the melt pool depth and width; there is an increase in the depth of the weld pool by 10%, while the change in the width of the weld pool (in the crown) is insignificant. [PERSON] et al. obtained similar results using GTAW\(-\)P and oxygen as surface active elements [31]; however, their mathematical model [32] suggests that within the range of 280-500 ppm oxygen content, the penetration remains nearly constant.