## 4 Conclusions  
This paper focused on the performance differences of AM centrifugal impellers compared with a centrifugal impeller manufactured by means of classical machining, in terms of production time, mass, and hydraulic efficiency (as a function of roughness). As the main applications foreseen for these components are the mechanically pumped fluid loop cooling systems for the space industry, time, cost, and performance are key elements. Dimensional analysis showed that the AM impellers presented higher dimensional stability when compared to the classical machined one, mainly due to the welding operations between the impeller disc and shroud. From a dimensional point of view, the AM aluminum impeller presented the highest accuracies. Although the AM impellers' interior roughness was considerably higher and uneven, the measured unbalance was lower than that imposed in [25], which validated the correctness of the printing process in terms of geometrical accuracy. Both X-ray CT and DLP analyses showed no defects on the AM impellers, which allowed them to be evaluated on the test bench. Thus, it can be concluded that the additive manufacturing process for fabrication of centrifugal impellers of small dimensions (less than 50 mm) is possible as a substitute for classical machining, especially when two or more processes are performed (as in the case of the classical machined impeller). Defect-free and dimensionally accurate parts were formed using AM technology under lower amounts of time and associated costs. Also, it was demonstrated that the high roughness of the AM impellers did not interfere drastically with their performance; however, the interior finishing processes for such small impellers are currently under study. Figure 16: Pressure rise comparison. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Impeller** & **Speed (rpm)** & **Flow (kg/h)** & **Pressure Rise (bar)** & **Efficiency (\%)** \\ \hline \multirow{2}{*}{Classical—AISI316L} & 11,208 & 619.97 & 1.61 & 33.31 \\ \cline{2-5}  & 12,015 & 598.16 & 1.84 & 30.12 \\ \hline \multirow{2}{*}{AM—Aluminum} & 11,222 & 618.02 & 1.57 & 31.77 \\ \cline{2-5}  & 11,999 & 596.81 & 1.79 & 29.76 \\ \hline \multirow{2}{*}{AM—Titanium} & 11,217 & 616.94 & 1.62 & 31.94 \\ \cline{2-5}  & 12,016 & 600.34 & 1.86 & 30.42 \\ \hline \multirow{2}{*}{AM—Inconel 625} & 11,214 & 618.03 & 1.63 & 31.49 \\ \cline{2-5}  & 12,000 & 599.03 & 1.87 & 28.75 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Duty and contingency point results. Further studies will aim to investigate the different interior finishing processes available to such complex shaped parts, the influence of the interior finishing process on the dimensional and geometrical accuracies of the blades and flow channel, as well as the hydraulic performance comparison. Conceptualization, I.-F.P., C.D. and I.S.V. ; methodology, I.-F.P. and I.S.V. ; software, C.D. ; validation, D.M., I.T. and A.M.C. ; investigation, I.-F.P. and I.S.V. ; data curation, I.T. and A.M.C. ; writing--original draft, I.-F.P., I.S.V. and C.D. ; writing--review and editing, D.M. and D.E.C. ; supervision, D.E.C. ; funding acquisition, D.M. ; project administration, D.M. All authors have read and agreed to the published version of the manuscript. The presented work was performed under two projects, namely, the \"NUCLEU\" program, in the frame of the National Research, Development, and Innovation Plan 2022-2027, carried out with the support of the Romanian Ministry of Research Innovation and Digitalization, Project No. PN23.12.06.01, and \"Development of a Closed Impeller Using Advanced Manufacturing\", Contract No. 4000137441/22/NL/MG/ces, funded by the European Space Agency (ESA). Not applicable. The data presented in this study are available upon request from the corresponding author. Due to the contract agreement between COMOTI and the funding agency, the research activities and data presented in this paper will be presented in an Executive Summary Report and will be available for public use after project closure.