## 4 Results and Discussion
### Experimental Results  
#### 4.2.1 Experiments without Shield Gas Chamber  
The result of the data analysis with Python of the oxygen point grid experiments of the three-jet nozzle are depicted in Figure 8.  
Figure 8 shows a pronounced three-jet symmetry of the oxygen concentration distribution, which results from the nozzle geometry. The openings of the powder channels of  
Figure 8: Detailed view of the center with low oxygen concentrations for the three-jet nozzle. Figure 7: Parametric sweep of the carrier gas volume flow and shield gas volume flow of the coaxial nozzle. **Top**: Oxygen concentration in an isometric view. **Bottom**: Oxygen concentration on workpiece surface. the three-jet nozzle are located at the extended points of the contour lines. The symmetry results in a directional dependence of the three-jet nozzle in relation to the spatially present oxygen concentration distribution. The result of the data analysis of the oxygen point grid experiments of the coaxial nozzle are shown in Figure 9.  
Figure 9 shows a sharp, defined center of low oxygen concentrations. Over a range of approximately a 7 mm radius, an oxygen concentration smaller than 10,000 parts per million (ppm) oxygen can be achieved. Furthermore, there is no directional dependence of the coaxial nozzle. In general, in contrast to the three-jet nozzle, a more homogeneous picture of low oxygen concentration is obtained. Since the carrier gas flow is spatially introduced equally from all the spatial directions, a radial symmetry of the oxygen concentration distribution results. Therefore, the carrier gas flow has less influence on the shield gas flow, resulting in less turbulence disturbing the shield gas cap. The influence of the volume flows is shown subsequently. Figure 10 shows the influence of the carrier gas flow on the existing oxygen concentration at the working distance of the respective nozzle centered above the hole plate. The carrier gas flow has an influence on the existing oxygen concentration. The standard deviation of the measuring points was determined based on three measurements. It is not visible in the diagram because the standard deviation for all measurements is less than 200 ppm and thus smaller than the marking of the points in the diagram. Thus, a statistical significance of the carrier gas volume flow on the oxygen concentration is given. Furthermore, the coaxial nozzle is less sensitive to carrier gas flow variation. In general, it can be stated that the oxygen concentration increases with increasing carrier gas volume flow (see trend line in Figure 10), and the coaxial nozzle is more robust to an increase in carrier gas volume flow in comparison to the three-jet nozzle. Figure 11 shows the influence of the shield gas flow on the existing oxygen concentration at the working distance of the respective nozzle centered above the hole plate. Figure 9: Spatial oxygen distribution of the coaxial nozzle. As the shield gas flow increases, the oxygen concentration decreases. The spread of the oxygen concentrations (e.g., at a shield gas flow of 7.5 L/min) results from the fact that a higher carrier gas volume flow was used at the higher oxygen concentrations--in contrast, lower carrier gas volume flows were used at lower oxygen concentrations at a shield gas flow of 7.5 L/min. It can also be seen that the coaxial nozzle tends to have lower oxygen concentrations with the same shield gas flow. Looking at the gradients of the trend lines, the carrier gas volume flow has a greater influence on the oxygen concentration present than the shield gas flow. This proves that a suitable adjustment of the carrier gas volume flow has a significant influence on the spatial oxygen distribution on the melt pool surface. Figure 11: Influence of the shield gas flow on the present oxygen concentration. Measurements were carried out directly above the hole plate in the working distance of the respective nozzle. Figure 10: Influence of the carrier gas flow on the present oxygen concentration.