# Analysis of Building Platform Inhomogeneities in PBF-LB/M Process on Alloy 718
## 3 Results and Discussion
### Melt Pool Analysis  
Once the porosity analysis is completed, the specimens are etched in the solution of oxalic acid to highlight the Melt Pool boundaries as shown in Figure 10.  
Figure 8: Interaction plots for porosity overview: (**a**) Differential pressure vs. position; (**b**) Differential pressure vs. exposed area; (**c**) Position vs. exposed area. Figure 9: Contour plot of porosity percentage measured as function of exposed area, position and differential pressure: (**a**) Low level; (**b**) Nominal level; (**c**) High level. The results of the Melt Pool Depth are shown in Figure 11 (and listed in Table A3) as a function of the tested parameters, and Figure 12 shows the main effect plot to identify the effects of the Exposed Area, Position, and Differential Pressure on the Melt Pool Depth. Figure 11: Melt pool depth as a function of exposed area, position and differential pressure variation. The 60 microns reference line (RL) is calculated according to [21]. Figure 10: Example of melt pool shape variation as a function of exposed area for position 4 and differential pressure set to nominal value: (**A**) exposed area of 70%; (**B**) exposed area of 59%; (**C**) exposed area of 37%. All images refer to the specimen located at position 1 in Figure 1.  
Evaluating the main effect plots for the Melt Pool Depth, as shown in Figure 12, for each tested parameter, a distinct and clear main effect is identified. As the Differential Pressure is reduced, the Melt Pool Depth decreases (consequently leading to the remelting of the underlying layer). While on the other hand, moving from the left to the right side of the building platform and reducing the Exposed Area, it should be noted that the Melt Pool Depth increases. These results agree with the Track's stability assessment and Porosity analysis as discussed in the previous section. Furthermore, the considerations that were made for the Porosity analysis are found to be valid also for the Melt Pool Depth analysis. One important aspect that should be noted in this analysis is the way production of spatter particles is increased significantly with the increase in the Exposed Area. On the contrary, lowering the Differential Pressure reduces the laser energy absorptivity of the powder bed that hinders the effective interlayer conductive heat transfer. As a result, a shallow Melt Pool just over 10 microns deep or even absent in some cases leads to a Lack of Fusion melting regime (as shown in Figure 10A,B) during the printing phase. Figure 13 represents the interaction plot to identify the interactions between Exposed Area, Position, Differential Pressure and Melt Pool Width, respectively. From Figure 13, the results indicate an absent or very low level of interaction between the various parameters on the Melt Pool Width. However, further analysis was performed to verify the main effects on the Melt Pool Width in terms of the same three parameters, taking into account the considerations that were made for the porosity analysis. The results of the Melt Pool Width are shown in Figure 14 (and listed in Table A3) in terms of Average and Standard deviation. The main effects plot is shown in Figure 15. The method that was employed to perform the main effects analysis is the same that was employed to evaluate the Melt Pool Depth. Figure 12: Overview of main effect of exposed area, position and differential pressure on melt pool depth. Figure 14: Melt pool width as a function of exposed area, position and differential pressure variation. The 90 microns reference line RL is calculated according to [21]. Figure 13: Interaction plots for melt pool depth overview. Interaction plots overview: (**a**) Differential pressure vs. position; (**b**) Differential pressure vs. exposed area; (**c**) Position vs. exposed area. Evaluating the Main Effect plots for the Melt Pool Width, shown in Figure 15, it is possible to identify for each tested parameter a distinct and clear main effect.