**6. Shaft-Hub Connection**

The transferability of model-based static COF´s to real components was recently demonstrated for mechanical manufacturing processes [55]. However, in this study a shaft-hub connection was chosen to transfer the advanced tribological performance of laser textured surfaces to a real-life application for the first time. The shaft diameter was 40 mm with H7 press fit for the shaft-hub connection. As a reference, the static COFs were determined of μ<sup>20</sup> = 0.20 and 0.24 for this specific shaft-hub connection considering a turned or rather fine-grinded surface quality of the contact area [34]. In this very initial test, the width of the laser textured area was 50 mm, as can be seen in the topographical analysis in Figure 15, left. Three different laser textures were analyzed: (i) the LSFL texture of Figure 10, (ii) the line pattern of Figure 12 and for reference purposes (iii) a dimple-shaped micro texture produced with a nanosecond laser as described in a previous study [14]. The frictional performance was analyzed by using a specially designed test rig for joined real components. The surface pressure varied in the measurements that was due to manufacturing tolerances of the shaft-hub assembly. The recorded slipping curves can be seen for the three different laser textures in Figure 15, right. Therefrom, the static and the maximum COFs μ<sup>20</sup> and μmax as well as the COF type were assessed. It is noteworthy, all COF values determined for the laser textured shaft-hub connection are larger than that for the non-laser textured contact surfaces. Table 2 shows the highest static COF for the line-patterned laser texture, μ<sup>20</sup> = 0.34 Type A while the maximum COF μmax = 0.4 was obtained with the dimple textured surface. Thus, the maximum COF increase was found of about + 20% for the LSFL, + 70% for the line pattern and + 100% for the dimple-shaped laser texture, respectively.


**Table 2.** Summary of the tribological characteristics of the different laser textures tested in a shaft-hub connection.

**Figure 15. left:** Topographical analysis of the shaft, the laser textured area is on the left shaft end; **right**: slipping curves captured in the frictional tests using a test rig for joined real components.

The processing rates given in Table 2 for the LSFL and line pattern, however, are noticeably lower than that presented above in Table 1 for ultrafast laser beam scanning. Therefore, it should be mentioned the processing rates in Table 2 are derived from the total processing time as spent for this specific shaft laser texturing using a galvanometer scanner at this very initial state. By further optimizing the laser texturing implementing polygon-mirror based and multi-beam strategies here, a substantially increase of the processing rates will also be achieved for rotational parts.
