Analysis of the Chemical and Tribological Properties of Phosphate Glass Layers Developing during Metalworking Processes on Manual Transmission Synchronizers*

Abstract

Abstract Optimization of machining processes to improve the tribological properties of surface layers has become a subject of industrial development. The modifications caused by manufacturing commonly include changes of topography, hardness or residual stresses. The present study investigates modification of the tribological properties of gear synchronizers by the formation of chemical layers on the metal surface within the final grinding process. These layers similar to phosphate glass emerge from the metalworking fluid additive zinc dialkyldithiophosphate (ZnDTP), which is applied in the process in different concentrations. The layers generated at the surface were measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Tribological experiments were conducted on a special synchronizer test facility. ToF-SIMS depth profiling revealed that higher ZnDTP concentrations in the metalworking fluid led to thicker phosphate glass layers on the machined surface. The layer that was generated by the addition of 5 % ZnDTP to the metalworking fluid led to a more homogenous coefficient of friction and a lower amount of wear in the tribological experiments. However, the addition of further ZnDTP, up to a total amount of 10 %, led to higher fluctuations in the coefficient of friction and increasing wear, likely related to the occurrence of friction oscillations resulting from thicker phosphate glass layers. However, the results indicate a good potential for improving surface layer properties of metal workpieces by adjusting the chemical composition of the metalworking fluid applied in the final machining process.