# Tribological Analysis of Fused Filament Fabrication PETG Parts Coated with IGUS
## 2 Experimental Procedure  
As explained, this study analyses the behaviour of multi-material parts manufactured with fused filament fabrication (FFF). Given that the objective of the study is not to develop a new material but to leverage the capabilities of existing commercial materials, in all cases, known materials with previously studied properties will be used, seeking a novel application for which no prior knowledge exists. Therefore, a commercial 1.75 mm diameter filament will be used, specifically, PETG and IGUS Iglidur 150 tribofilament, expressly developed for dynamic contact motion applications [22]. Circular specimens of 70 mm in diameter and 2 mm in thickness have been manufactured, with these materials using a commercial FFF equipment equipped with a 0.4 mm diameter extruder nozzle. Within the manufacturing parameters, extrusion speed of 60 mm/s, a filament overlaps of 55%, a build platform temperature of 60 \({}^{\circ}\)C, and 100% fill have been established as constants. Additionally, Archimedean chords fill geometry has been used. This is to ensure that the material deposition direction is consistent with the sliding direction of the tribological tests. In this way, changes in the surface texture of the parts do not alter the tribological results. These parameters have been selected based on previous studies [10; 11; 28; 29]. Figure 1 presents the scheme of the specimens and manufacturing strategies. For multi-material manufacturing, two manufacturing phases have been programmed, with an intermediate stop for material change and manufacturing parameters. Thus, two extrusion temperatures have been used: first, PETG required 230 \({}^{\circ}\)C, while IGUS tribofilament required 250 \({}^{\circ}\)C. The manufacturing parameters are listed in Table 1. These parameters are those recommended by the filament manufacturers. This programmed change was made to create an IGUS coating layer on PETG of a certain thickness. Since a layer thickness of 0.3 mm has been programmed for the entire specimen, this coating will be 0.3 mm (one-layer coating), 0.6 mm (two-layer coating), and 0.9 mm (three-layer coating). Prior to the manufacture of the specimens, a metrological calibration of the manufacturing equipment was carried out to guarantee the layer thicknesses deposited in each case. Subsequently, the manufactured specimens were subjected to pin-on-disc (PoD) tribological tests following ASTM G99 standards [30] using a Microtest MT NI series equipment (Microtest, Madrid, Spain). Due to the lack of specific standards, this study used methodologies validated in previous studies [10; 11], based on the general standards of the test [30]. In this way, for the performance of pin-on-disc tests, the linear test speed will be a constant \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Material** & **T (\({}^{\circ}\)C)** & \
\begin{tabular}{c} **Layer Thickness** \\ **(mm)** \\ \end{tabular} & **Extrusion Velocity (mm/s)** & **Overlap** & **Bed Temperature (\({}^{\circ}\)C)** & **Infill** \\ \hline PETG & 230 & 0.3 mm & & & & \\ \hline Iglidur I50 & 250 & 0.3 mm & 60 & 55\% & 60 &
\begin{tabular}{c} Archimedean \\ chords (100\%) \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Materials and manufacturing parameters. Figure 1: Scheme of specimens and manufacturing strategies. 105 mm/s, and the total distance travelled by the pin will be 250 m. The testing parameters are listed in Table 2.  
Using the coefficient of friction (CoF) data obtained in the tests, the evolution of the test will be calculated by calculating a moving trend line and an average coefficient of friction value obtained as an arithmetic mean of the data obtained in the intermediate 150 m of each test. Similarly, the amplitude of the CoF will be calculated as the distance between the average of the three highest peaks and the three deepest valleys. Additionally, all specimens will be analysed using stereoscopic optical microscopy before and after the tests, as well as the pins used and any detached particles or debris.