Under oil-free lubrication conditions, flexspline wear is a main cause of performance degradation in harmonic reducers, severely affecting their transmission performance and service life. A comparative study of the wear performance and wear mechanisms of the flexspline material, the steel wheel material, and the flexible bearing material under dry friction conditions is conducted to provide experimental evidence and theoretical support for material selection and matching design of high-wear-resistance, long-life harmonic reducers, thereby enhancing their transmission reliability and extending their service life.
The finite element method is employed in conjunction with the actual working conditions of the harmonic reducer to analyze the contact pressure between the flexspline and the circular spline, as well as between the flexspline and the flexible bearing. The obtained contact pressure is then converted into the required loading conditions for experimental validation. A pin-on-disk friction and wear test is designed with a heavy-duty reciprocating friction and wear tester. Based on the results of friction coefficient and wear rate, the dynamic behaviors of the friction interface under different working conditions are investigated. Furthermore, scanning electron microscopy (SEM) images and energy-dispersive X-ray spectroscopy (EDS) data are utilized to conduct an in-depth analysis on the wear mechanisms of the two contact pairs under dry friction conditions.
Research indicates that for both GCr15/40CrNiMoA and 45 steel/40CrNiMoA contact pairs, the time required for the friction coefficient to stabilize is shorter under higher loads or frequencies. After stabilization, the average friction coefficient increases with the increasing load but decreases with the increasing frequency. In contrast, the wear rate gradually decreases with the increasing load, while it increases with the increasing frequency. Under the same operating conditions, the wear rate of the GCr15/40CrNiMoA pair is slightly higher than that of the 45 steel/40CrNiMoA pair. For the 45 steel/40CrNiMoA contact pair, under low load and low frequency conditions (300 N, 3 Hz), severe abrasive wear and adhesive wear dominate. At higher loads (400 N, 3 Hz), the wear mechanism transitions to mild abrasive wear and oxidative wear. Under higher frequency conditions (300 N, 5 Hz), thermal softening effects intensify material extrusion delamination and block-like spalling, leading to an increased wear volume. In contrast, for the GCr15/40CrNiMoA friction pair, under low load and low frequency conditions (400 N, 3 Hz), mild adhesive wear and abrasive wear are observed. At higher loads (500 N, 3 Hz), spall pits formed by the fracture of oxide films appear, with wear debris contributing to load-bearing. Under higher frequency conditions (500 N, 5 Hz), intensified cyclic stress promotes fatigue crack propagation and three-body wear, resulting in a significant increase in wear severity.
The worn surface of the GCr15/40CrNiMoA tribological pair displays significant delamination and a rough topography, indicative of severe wear. Conversely, for the 45 steel/40CrNiMoA tribological pair, the similar hardness levels of the two materials lead to a more uniform stress distribution across the contact interface, effectively mitigating severe unilateral cutting. The worn surface is smooth, exhibiting only shallow wear tracks with no evident delamination or spalling, thus demonstrating enhanced wear resistance. Accordingly, the 45 steel/40CrNiMoA tribological pair shows superior wear performance.
Key words
flexspline wear /
finite element simulation /
pin-on-disk test /
friction coefficient /
wear rate /
wear mechanism
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