## 4 Discussion  
Herein, the effect of seven generic 3D printing settings on the compressive strength and the energy demands for the fabrication of PA6 parts with the MEX method is presented. Experiments were conducted, and the findings were analyzed with statistical modeling. The aim was to locate a set of 3D printing parameters that optimize both the compressive strength and the energy demands for the manufacturing of the corresponding parts. Through the analysis of the results and the modeling process followed it was found that specific 3D printing settings highly affect the performance of the produced parts, and overall, all the 3D printing settings studied contribute to the performance of the parts. For the first time, the compressive strength of PA6 3D printing is studied in such depth (as a function of seven 3D printing settings), revealing once again the importance of selecting proper 3D printing in the MEX process. Additionally, for the first time, according to the authors' best knowledge, insight into the required energy to 3D print PA6 parts with the MEX method is provided, along with a roadmap on the effect of the 3D printing settings, suggesting the values that achieved more sustainable and eco-friendly results. Sustainability, as mentioned, is a critical parameter nowadays for the AM process. No set of parameters was possible to optimize both the compressive strength and the energy consumption, suggesting that a compromise needed to be made in one or the other direction (mechanical performance or eco-friendliness). Still, specific parameters could achieve more or less good results for both contradictory measures. For example, a 0 deg ORA achieves high compressive strength with reduced energy demands. RDA does not highly affect both measures; the PS and the BT do not significantly affect the compression strength, while their high values significantly reduce the energy demands for the manufacturing of the parts. The NT parameter is not highly affecting the energy demands, while its increase results in higher compressive strength values. The two control parameters that contradict each other are the LT and the ID. High LT values reduce the energy demands but also the compressive strength, while high ID values increase the compressive strength but also the demands. The ID can affect the compressive strength by almost 300%. This is approximately the difference between the lowest and the highest value recorded by altering only the specific control setting. It should be noted that the literature on the compressive strength of PA6 parts in MEX 3D printing is very limited. Still, the results are in good agreement with the existing literature [88]. The PS, on the other hand, can double the energy demands, with lower PS values requiring twice the energy of the higher values to build the parts (without significantly affecting the compression strength, as mentioned). Such differences justify the need for the analysis carried out in the current work. It should be noted that the EPC values follow the same pattern as the Printing Time values, showing a strong relationship between these two measures. The energy consumption results cannot be directly correlated to the literature since, to the authors' best knowledge, no study so far has presented corresponding results. Comparing the results presented herein with \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Run** & & **28** & **29** \\ \hline \multirow{3}{*}{Actual} & sB (MPa) & 36.94 & 3.26 \\  & EPC (MJ) & 0.78 & 0.12 \\ \cline{1-1}  & sB (MPa) & 41.30 & 3.56 \\ \cline{1-1}  & EPC (MJ) & 0.75 & Vague \\ \cline{1-1}  & sB (\%) & 11.79 & 8.95 \\ \cline{1-1}  & EPC (\%) & 3.97 & Vague \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Validation Table A.  
corresponding results for the ABS polymer [18], the PA6 polymer requires higher energy amounts to be 3D printed. LT and PS were also dominant parameters in the ABS study regarding energy demands. Similar findings are reported for the PLA [19], the PMMA [21], and the PC [22] polymers, as well.