Gear transmissions are usually run under mixed friction, i.e. the tooth flanks are not completely separated by an oil film. Boundary layers, which develop on the surfaces during manufacturing and application, can protect tooth flanks from metal-metal contacts. The characteristics of boundary layers and the running behavior are determined by the preconditioning processes (finishing and run-in) and by the application itself.
This paper focuses on the development of boundary layers and on their modes of action in two-disk contacts. The investigation comprises boundary layer analyses (FIB-SEM, SNMS) and two-disk tests regarding lifetime and friction force. The test parts and test conditions are chosen in ways that resemble real gears. The surface layer analyses show that the processes of manufacturing, run-in and application affect the boundary layer system and influence the running behavior of the produced parts. Therefore, the interaction between the surfaces, the manufacturing fluid and the transmission oil is evaluated in finite life fatigue testing (pitting) and efficiency measurements (friction) on two-disk test rigs. By combining the test results and the boundary layer measurements, correlations between manufacturing and operation are investigated to establish a more sustainable and economical design of gears.