Boundary layers, which develop during manufacturing and operation, can protect tooth flanks from metal-to-metal contacts. The characteristics of boundary layers and the running behavior of gears are determined by the preconditioning processes (manufacturing and run-in). This paper aims to analyze the influence of the grinding process parameters and the grinding oil on the characteristics of boundary layers.
Sets of test parts and test gear sets with different grinding process variants and different metalworking fluids were manufactured to investigate the mechanisms of action of thermomechanical and chemical surface preconditioning during grinding. The test parts were analyzed with regard to their boundary layer by metallography and chemistry and regarding their running behavior on test rigs lubricated with transmission oil.
In the tests, reproducible differences in gear strength regarding low-cycle fatigue and micropitting were determined for the test parts ground with different thermomechanical energy inputs and with different metalworking fluids. As the test results could not be sufficiently explained on the basis of conventionally tolerated component properties such as roughness, hardness and residual stresses, a model was discussed which combines the mechanisms of action of the formation of the manufacturing-induced boundary layer with the running behavior of the parts.
By combining both measurement and test results, possible correlations between manufacturing and operation are investigated to establish a more sustainable and economical design of gears.
