# Tribological Analysis of Fused Filament Fabrication PETG Parts Coated with IGUS
## 3 Results
The low significance of the friction coefficient with the coating thickness makes sense because although increasing the coating thickness may prolong the contact area over time, as long as this coating does not wear out, the tribological pair remains the same in all cases. Therefore, the friction coefficient should be similar since the same materials are in contact. The correlation in this case is somewhat clearer as it shows that regarding the coefficient of friction, the correlation is weakly negative with both coating thickness (\(-0.251\)) and load (\(-0.109\)), but the amplitude shows a moderate negative correlation with coating thickness (\(-0.602\)) and an even greater correlation with load (\(-0.769\)). These results indicate that coating thickness and applied load have different levels of influence on the average coefficient of friction and the coefficient of friction amplitude. The moderate negative correlation between coating thickness and coefficient of friction amplitude is consistent with previous studies showing that antifriction coatings can improve tribological behaviour by reducing friction variability. The strong negative correlation between applied load and coefficient of friction amplitude also suggests that a higher load can stabilise tribological behaviour, which has been reported in the literature [39; 40]. Analysing the generated groove, more linear behaviours appear. Analysing the groove width (Figure 9), it is observed that increasing the load increases the width in all cases, and at equal load, increasing the coating thickness results in less material loss. This aligns with the previously hypothesised trends. Regarding groove depth (Figure 10), the behaviour is similar, indicating that the wear behaviour of the parts is very homogeneous and stable. In this case, the statistical analysis (Table 5) reveals that coating thickness has little significance with respect to the groove width (F = 0.147; \(p\)-value = 0.7145) and groove depth (F = 0.488; \(p\)-value = 0.5110). In both cases, the F-value is very low, and the \(p\)-value is much greater than 0.05, indicating that variability in groove width and depth is not significantly influenced by coating thickness under the conditions of this study. This does not occur with load, which has significance with respect to groove width (F = 13.704; \(p\)-value = 0.0101) and groove depth (F = 15.495; \(p\)-value = 0.0077). In this case, the F-value is high, and the \(p\)-value is less than 0.05, indicating that he applied load has a statistically significant effect on groove depth and width. Although there is no significance in the interaction of both factors. These results indicate that the applied load has a significant \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Coating** & **Coefficient** & **Load** & **Amplitude of** & **Coefficient** & **Load** \\
**Thickness** & **of Friction** & & **the Friction** & **of Friction** & **load** \\ \hline F-value & 0.811 & 4.256 & 0.584 & F-value & 0.459 \\ \(p\)-value & 0.4024 & 0.0847 & 0.4737 & \(p\)-value & 0.5233 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: ANOVA results of coating thickness and coefficient of friction. Figure 8: Particles detached during the tribological tests. However, as observed in the graphs, there is a correlation between groove width and coating thickness (0.828) and load (0.950) and between groove depth and coating thickness (0.806) and load (0.946), with all cases showing strong positive relationships, especially with load, verifying the previously observed trends. These results indicate that both coating thickness and applied load have a significant influence on groove width and depth. The strong positive correlation with load is consistent with previous studies showing that applied load during tribological tests has a notable impact on groove dimensions due to direct mechanical interactions between contact surfaces.