## 2 Materials and Methods
### Welding Parameters  
The welding process of the test specimens was organized into six groups. Two of them (groups P0 and P3) were selected due to parameter variability and discrepancies found in the literature and were used to evaluate how different process conditions affect the weld. Although most of the reviewed literature suggests a tilt angle on the tool, this study also tested welding with a tilt angle of 0\({}^{\circ}\), as an extreme case, in order to observe the resulting effects. Therefore, group P0 consisted of parameter tests for material addition in specimens with 15% infill and a tool tilt angle of 0\({}^{\circ}\), whereas group P3 included specimens with 100% infill and a tool tilt angle of 8\({}^{\circ}\). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & **Specimen** & **Specimen** & **Parameter** & **Specimen** & **Specimen** \\  & **Fill 15\%** & **Fill 100\%** & & **Fill 15\%** & **Fill 100\%** \\ \hline \multicolumn{2}{c}{**Quality**} & \multicolumn{3}{c}{**Speed (mm/s)**} \\ Layer height (mm) & 0.2 & 0.2 & Print speed (mm/s) & 60 & 60 \\ \hline \multicolumn{2}{c}{**Wall**} & \multicolumn{3}{c}{Travel speed (mm/s)} & 120 & 120 \\ Wall thickness (mm) & 0.8 & 2 & Infill speed (mm/s) & 60 & 60 \\ \hline \multicolumn{2}{c}{**Material**} & \multicolumn{3}{c}{Top/bottom layer speed (mm/s)} & 30 & 30 \\ Retraction & \multicolumn{3}{c}{Outer wall speed (mm/s)} & 40 & 40 \\ Initial layer thickness (mm) & 0.3 & 0.3 & Inner wall speed (mm/s) & 60 & 60 \\ \multicolumn{2}{c}{Extrusion expansion (\%)} & 100 & 100 & \multicolumn{1}{c}{**Cooling**} & \\ Extrusion overlaps (mm) & 0.15 & 0.15 & Minimum time per layer (s) & 5 & 5 \\ \hline \multicolumn{2}{c}{**Support**} & \multicolumn{3}{c}{Enable cooling fan} & Yes & Yes \\ \multicolumn{2}{c}{\begin{tabular}{c} Support \\ Adhesion structure type \\ Skirt thickness (mm) \\ \end{tabular} } & No & No & \multicolumn{2}{c}{**External infill**} \\ \multicolumn{2}{c}{\
\begin{tabular}{c} Adhesion structure type \\ Skirt \\ \end{tabular} } & Yes & Yes & \multicolumn{1}{c}{Top/bottom thickness (mm)} & 0.6 & 0.8 \\ \multicolumn{2}{c}{
\begin{tabular}{c} Infill direction (\({}^{\circ}\)) \\ Top/bottom infill direction (\({}^{\circ}\)) \\ \end{tabular} } & 0 & 0 \\ \hline \multicolumn{2}{c}{**Infill**} & \multicolumn{3}{c}{**Machine**} \\ Solid top infill & Yes & Yes & Nozzle diameter (mm) & 0.4 & 0.4 \\ Solid bottom infill & Yes & Yes & \multicolumn{1}{c}{**Temperature**} & \\ Infill density (\%) & 15 & 100 & Bed & 40 & 40 \\ Infill pattern & Grid & Grid & Nozzle & 215 & 215 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The main parameters for specimen printing. Each parameter group is highlighted in bold, with the corresponding values listed below for 15% and 100% infill. Figure 5: (**a**) The structure of an internal layer (orange) of a complete specimen with two perimeters: 15% infill density, 0–90\({}^{\circ}\) orientation, and a layer height of 0.2 mm. (**b**). The internal structure (orange) of a specimen processed with 15% infill in a 0–90\({}^{\circ}\) orientation. In groups P1 and P2, the welding process was performed on specimens with 15% infill density using tool tilt angles of 0\({}^{\circ}\) and 8\({}^{\circ}\), respectively, while varying the feed rate. Groups P0, P1, P2, and P3 were welded without a tool pin. In these cases, the filler material rod itself generated the necessary friction and heat. The welding tests for groups P4 and P5 were performed without material addition on specimens with 100% infill, using Tool 1 and Tool 2 geometries, respectively. The variables considered and measured during the tests are as follows:  
Rotational speed, measured in rpm. Welding speed, measured in mm/min. Tool tilt angle, measured in degrees, as shown in Figure 6a,b. Material feed speed, measured in mm/min. Welding direction (forward or backward).