Manufacturing of tribologically optimized surfaces for powertrain applications

Among the major interests in powertrain development are the reduction of frictional losses and service life extension from improved wear resistance. Surface finishing and deterministic microstructuring have been shown to be effective methods in improving the tribological properties of sliding contacts such as bearings and cylinder liners. This is due to their acting as micro pressure-chambers and as wear debris traps. In this work, tribometric ring-on-disc tests were performed in order to evaluate the influence of surface structure - namely, the microstructure geometry and layout - on the frictional behavior of lubricated surfaces. The material combination bronze against steel as typically used in powertrain applications was investigated. The surface structures where machined using electrochemical machining by closed electrolytic free jet (Jet-ECM). It was determined that microstructuring reduced the friction coefficient by up to 45 % in the hydrodynamic regime under loads and speeds found in automotive components. The friction measurements showed that microstructures with low aspect ratios result in the least friction. In addition to the tribological investigations, the process capabilities and implementability in serial production of two surface microstructure fabrication processes: Jet-ECM and a newly developed, hybrid roller micro-embossing and burnishing process were evaluated and contrasted. It was shown that both fabrication methods can attain high structure quality.