## 3 Results and Discussion
### Mass Determination and Material Loss  
The mass of the specimens was measured before and after welding in order to determine the amount of filler material added and the material loss in the form of chips. The mass of all specimens was measured before welding in pairs. Then, the reference unwelded masses were 11.9844 \(\pm\) 0.0355 g and 20.1936 \(\pm\) 0.0363 g for the 15% and 100% infill percentages, respectively. The results of the masses for each pair are shown in Table 3. Data comparison with the reference is also shown in Figure 12a,b in a bar and box-and-whisker plot. Figure 11: (**a**) The bottom view of the specimen P2_3 (left) and a schematic representation of the material flow from the filler rod to the material voids, which is visible from the bottom side; (**b**) the bottom view of the specimen P5_3 (left) and a schematic representation of the stir zone, which is visible from the bottom side. * In Figure 12a, the dashed line indicates the reference value, confirming that in the P0 specimen group, very little filler material was added, as the lack of tool inclination prevented the flow of the filler material, as previously shown in Figure 8c. In the P1 specimens, with 15% infill and filler rod, a noticeable mass increment was reported. In the P2 specimens, the amount of filler material added was slightly less than that in the P1 group, which was due to the narrower weld caused by the increased travel speed. The mean width of the weld for low and high welding speeds was 5.42 and 3.22 mm, respectively. This effect is clearly visible in Figure 13a,b, where the black weld lines highlight the width differences. When the filler material flow rate was kept constant, higher welding speeds produced narrower weld lines to distribute the total added mass. ANOVA analysis on the specimen mass revealed statistically significant differences between the three groups (\(p<0.05\)). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **ID** & **Mass (g)** & **ID** & **Mass (g)** & **ID** & **Mass (g)** \\ \hline \multirow{4}{*}{**15\% Infill**} & **Test P0** & & **Test P1** & & **Test P2** & \\  & P0\_0 & 11.9303 & P1\_0 & 12.3080 & P2\_0 & 12.0844 \\  & P0\_1 & 12.0133 & P1\_1 & 12.1964 & P2\_1 & 12.0796 \\  & P0\_2 & 12.0288 & P1\_2 & 12.1785 & P2\_2 & 12.1022 \\  & & P1\_3 & 12.0580 & P2\_3 & 12.1499 \\ \cline{2-6}  & Avg. \(\pm\) SD & 11.9908 \(\pm\) 0.0530 & Avg. \(\pm\) SD & 12.1409 \(\pm\) 0.1024 & Avg. \(\pm\) SD & 12.1040 \(\pm\) 0.0321 \\ \hline \multirow{4}{*}{**100\% Infill**} & **Test P3** & & **Test P4** & & **Test P5** & \\  & P3\_0 & 20.1202 & P4\_0 & 19.8657 & P5\_0 & 19.9750 \\  & P3\_1 & 20.0859 & P4\_1 & 20.0550 & P5\_1 & 19.9830 \\  & P3\_2 & 20.0659 & P4\_2 & 20.0465 & P5\_2 & 19.9594 \\  & & & P4\_3 & 19.9687 & P5\_3 & 20.0544 \\  & & & P4\_4 & 19.9223 & P5\_4 & 19.9860 \\  & & & P4\_5 & 19.8941 & P5\_5 & 20.0681 \\  & & & P4\_6 & 20.0484 & P5\_6 & 19.8980 \\  & & & P4\_7 & 19.8060 & & \\ \cline{2-6}  & Avg. \(\pm\) SD & 20.0907 \(\pm\) 0.0275 & Avg. \(\pm\) SD & 19.9508 \(\pm\) 0.0942 & Avg. \(\pm\) SD & 19.9891 \(\pm\) 0.0576 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The mass of test specimens across different groups. Each group of specimens is highlighted in bold. The mass of each specimen is listed, along with the average and standard deviation below. The table includes specimens with both 15% and 100% infill. Figure 12: The mass of the specimen with (**a**) 15% infill with filler material and (**b**) 100% infill with filler material (P3) and without filler material (P4 and P5). Similarly, for the specimens with 100% infill density, the results are shown in Figure 12b. As expected, the mass of the specimens where filler material was added (test P3) was slightly higher, but still less than the base material mass. This means that during welding, more material was lost than gained. Significant differences were observed between P3 and the other two groups (\(p<0.05\)), P4 and P5.