# Tribological Analysis of Fused Filament Fabrication PETG Parts Coated with IGUS
## 3 Results
Thus, the thinner coating also behaves similarly as it does not have a high value of peaks but does have higher average values that homogenise as the thickness increases. This makes sense as the extrusion temperature significantly influences the surface quality of FFF printed parts. A higher extrusion temperature tends to improve interlayer adhesion, resulting in a smoother surface (lower Sa) and reducing peak height (lower Sz). This is because the molten material flows better and fills gaps between adjacent layers more effectively, reducing overall surface roughness [36; 37]. In this case, where one material is deposited on another, the interface is a problematic area, also due to the material change; therefore, increasing the number of layers of the new material improves quality. However, different materials react differently to temperature changes, and it should not be forgotten that a hotter material is overlaid on the substrate's melting temperature. However, it has been observed in reinforced materials that an increase in extrusion temperature also reduces surface roughness due to the better fusion and adhesion of the composite material [38]. In this case, this interface may be favoured by the higher extrusion temperature of the coating. Therefore, it is inferred that if the temperature of the second material were lower than the first, the result would be worse. Additionally, analysis of variance (ANOVA) was performed for three surface quality metrics--average Sa (\(\upmu\)m), average Sz (\(\upmu\)m), and average Sdc (\(\upmu\)m)--to analyse the significance of the antifriction coating thickness to the surface quality of FFF-fabricated specimens (Table 3). The ANOVA results provide information on whether the coating thickness has a significant effect on these metrics. For average Sa (\(\upmu\)m), the F-value obtained was 4.197, with a \(p\)-value of 0.0797. Although the F-value is relatively high, the \(p\)-value exceeds the 0.05 threshold, indicating no statistical significance at the 5% level. This suggests that although there is a trend where the coating thickness might be influencing the average roughness, this influence is not conclusive with the available data. In the case of the average Sz (\(\upmu\)m), the F-value was 2.774, with a \(p\)-value of 0.1398. This result shows a lower F-value and a \(p\)-value greater than 0.05, indicating no clear statistical significance in the effect of coating thickness on the maximum surface height. This implies that variability in average Sz is not significantly influenced by coating thickness under the conditions of this study. For average Sdc (\(\upmu\)m), the F-value was 4.355, with a \(p\)-value of 0.0753. Similar to the average Sa case, although the F-value is notable, the \(p\)-value remains greater than 0.05, indicating that the relationship between coating thickness and the surface cut depth is not statistically significant. Additionally, there is no significance in the interaction of both factors. However, the observed trend could indicate an influence that might be more evident with a larger sample size or more detailed studies. Although the results do not show statistical significance in this analysis, the observed trends are consistent with [PERSON] and [PERSON] [39], who analysed the possibility of using antifriction coatings and observed that a thicker coating could improve surface quality. Similarly, [PERSON] et al. [40] also found positive effects of surface modification on the tribological behaviour of FFF components, although this was a preliminary study. Similarly, it should be noted that in all three cases, there is a moderate negative correlation (Sa: \(-\)0.612; Sz: \(-\)0.533; Sdc: \(-\)0.619), suggesting that as coating thickness increases, quality tends to improve. This trend is consistent with the expectation that a thicker antifriction coating improves surface quality by reducing roughness.