## 3 Results and Discussion
### Wear Evaluation
The heat transfer enhancement of the hybrid polymer gears reduced their wear, and the hybrid polymer gears with the aluminum inserts were highlighted as the best solution based on both the measured minimum and mean base tangent length values. In all cases, a strong correlation between the gear bulk temperature and tooth flank wear was observed, with the hybrid polymer gears with the aluminum inserts showing the greatest improvement in performance. Apart from the initial wear-in phase, the tooth flank wear was mainly influenced by the increase in temperature and the softening of the material. In addition to the material softening, an existing difference in sliding velocities along the tooth flank facilitated material removal. Reduced tooth flank wear had a positive effect on the gear meshing condition, which led to less heating. The differences in tooth flank wear were also confirmed by comparing the measured weight of the gears before and after the measurement (Table 3). A weight loss of 0.38 g was measured for the lower- and higher-quality polymer pinions and 0.54 g for the polymer wheel, respectively. For the hybrid polymer gears with steel inserts, the weight loss of the pinion was 0.10 g, and for the wheel, it was 0.15 g. In the case of the hybrid polymer gears with the aluminum inserts, the weight difference before and after the test was the smallest: 0.05 g for the pinion and 0.10 g for the wheel. Figure 15a-d show four teeth from each of the wheel gears, with the highest tooth flank wear in relation to the measured base tangent length. The difference in the tooth profile deterioration between the polymer gears and the hybrid polymer gears was recognized. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Gears Weight** & **Pinion (BT/AT)** & **Wheel (BT/AT)** \\ \hline Polymer Gear (Fine) & 45.19 g/44.81 g & 38.17 g/37.63 g \\ Polymer Gear (Extra Fine) & 48.82 g/48.44 g & 39.82 g/39.28 g \\ Hybrid Polymer Gear with the Aluminum Insert & 49.57 g/49.52 g & 40.42 g/40.32 g \\ Hybrid Polymer Gear with the Steel Insert & 66.91 g/66.81 g & 55.25 g/55.10 g \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Weight measurements before (BT) and after (AT) testing. Figure 14: Base tangent length of the pinion and the wheel before (BT) and after (AT) testing. When the total weight of the gears is taken into account, the application of steel inserts in the polymer matrix increases the weight of the pinion by 18 g and the wheel by 15 g compared to the higher-quality polymer gears, which corresponds to a weight increase of 37%. On the other hand, the weight of the hybrid polymer pinion and the wheel with aluminum inserts increased by only about 2%, or slightly less than 1 g for each gear, thereby retaining the benefits of hybrid polymer gears over metal gears in terms of the low specific weight, just like the polymer gears. The present study focused on the experimental analysis of hybrid polymer gears, which is a novelty compared to previous work by [PERSON] et al. [43], which provided a thermal analysis based on FEM simulations. Although the intention was to experimentally validate the results from [43], differences in the tooth profile geometry, gear ratio and material prevented this. POM was not suitable for the FDM 3D printer used, so PA was used instead. However, the concept of a hybrid polymer gear concept presented in [43], which is similar to the first design of a hybrid polymer gear presented in this study, had several drawbacks and failed to complete the test. Other concepts were not applicable for this experiment. The benefits of this research manifest themselves in a new hybrid polymer gear design with improved thermal behavior and wear resistance, while the overall weight of the polymer gears remains low.