## 3 Results and Discussion
### 3D Printing
Despite the fact that the thickness of the blades has been reduced from 1.60 mm to 1.29 mm in average, the total material volume of the impeller increased from \(\sim\)4108 mm\({}^{3}\) of the original one to \(\sim\)6162 mm\({}^{3}\) of the printed one. This is due to the increased value of the thickness of the lower flared part (1.93 mm against 1.82 mm in average) and the full densification of the upper one chosen in order to guarantee a greater resistance of these sections and, therefore, the success of the SLM printing process. As a result, the 3D printed pump impeller has a greater weight of around 1.5 times higher than the original one and a more robust design, allowing to operate velocities with the same stress thus generating increased head [55]. Moreover, the reduction of the thickness of the blades, together with the simplification of their geometry by avoiding the use of extra overhangs for bending and welding, results \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Section**} & \multicolumn{8}{c}{**Model Dimensions [mm]**} \\ \cline{2-9}  & \multirow{2}{*}{**Original Impeller 1**} & \multirow{2}{*}{**CAD Model**} & \multicolumn{8}{c}{**SLM Printed Impeller**} \\ \cline{3-9}  & & & **\#1** & **\#2** & **\#3** & **Mean** & **Std** & **Err** \\ \hline Lower flared part & 1.82 & 1.90 & 1.93 & 1.93 & 1.94 & 1.93 & 0.005 & 0.03 \\ Upper flared part & 1.90 & 1.90 & 1.93 & 1.85 & 1.95 & 1.91 & 0.043 & 0.01 \\ Blade \#1 & 1.59 & 1.30 & 1.30 & 1.28 & 1.29 & 1.29 & 0.008 & 0.01 \\ Blade \#2 & 1.63 & 1.30 & 1.29 & 1.31 & 1.28 & 1.29 & 0.012 & 0.01 \\ Blade \#3 & 1.58 & 1.30 & 1.27 & 1.29 & 1.31 & 1.29 & 0.016 & 0.01 \\ Blade \#4 & 1.62 & 1.30 & 1.30 & 1.29 & 1.35 & 1.31 & 0.026 & 0.01 \\ Blade \#5 & 1.58 & 1.30 & 1.29 & 1.28 & 1.27 & 1.28 & 0.008 & 0.02 \\ Blade \#6 & 1.58 & 1.30 & 1.30 & 1.29 & 1.27 & 1.29 & 0.012 & 0.01 \\ \hline \hline \end{tabular} \({}^{1}\) Average values. Please, refer to Table 2 for details.  
\end{table} 
Table 8: Geometrical accuracy evaluation of the sections’ thickness of the 3D printed impeller through the measurement on three random points (indicated as #1, #2, and #3 for sake of simpleness). All the values are expressed in mm. “Std” stands for standard deviation; “Err” is the absolute error defined as the difference between the measured (average) and the estimated (from CAD model) values of the various thicknesses, is 1% for the blades and the upper flared part, while around 3% for the lower flared part. in an increased volume available for the fluid flow and therefore ensuring a higher flow rate, thus likely leading to an increased efficiency [56; 57]. However, it is worth noting that the pump efficiency strictly depends on the total energy losses, which can originate from sources of different physical nature. Among all, the mechanical friction losses are of particular importance [56]. Therefore, since the surface of the blades, as well as all the surface of the impeller as a whole, are characterized by a high roughness, a decrease in the pump efficiency is expected [58; 59] unless an appropriate finishing process is performed. But all of these aspects need further investigations, which were not part of the present study. In general, the SLM technique could represent a suitable alternative for the production of mechanical parts with characteristics comparable to traditional production techniques, but still require further processing of the components for obtaining the required surface roughness for the chosen application (i.e., the reproduction of the impeller of a submersible electric pump). However, this study further needs the investigation of the actual performance of the impeller during operation in order to evaluate the efficiency of the pump.