Optimising lubricated friction coefficient by surface texturing

Abstract

Surface texturing has proved to be a very useful tool for expanding the behaviour under hydrodynamic and elastohydrodynamic regimes instead of mixed or boundary lubrication regimes, and therefore for reducing the friction coefficient under high-load low-speed conditions. This article presents the texturing of different copper test-samples using photolithography and chemical etching to measure the friction coefficient using a point contact machine. The effects of texture size, texturing density, the initial roughness of the samples and the operating conditions have all been studied. Some combinations of texturing density and texture size achieve up to 30% reduction in the friction coefficient. Taking into account experimental data, artificial neural networks are used as a tool for both predicting and optimising the friction coefficient on the textured surface for any given operating condition.

Optimising the design of textured surfaces for reducing lubricated friction coefficient

“…The textures were created on a flat side of copper discs so as to subsequently test the point contact between a steel ball and the discs in a tribometer under 5 and 20 N loads, which correspond to the test conditions used in earlier studies …”

“…There are many techniques for removing material on metal surfaces in a controlled manner . The photolithography and chemical etching process has been chosen due to its simplicity and the efficacy shown in previous analyses . The photolithographic equipment used was the SF‐100 from Intelligent Micro Patterning (http://www.intelligentmp.com), which is shown in Figure .…”

“…The surface density ranged from 5 to 10%, according to the information available in prior works . Likewise, different combinations of time (8–20 min) and chemical etching temperatures (25–40°C) were used, which allowed — in the absence of conclusive prior studies on depth — a sufficient wide range to be obtained for analysis: 17, 35 and 78 µm.…”

“…In order to facilitate a comparison of the new results to those obtained previously, the materials chosen and the conditions selected for tests in the MTM tribometer were those used in earlier studies, i.e. normal loads of 5 and 20 N (equivalent to Hertzian pressures of 0.42 and 0.67 GPa respectively), PAO‐6 lubricant at a constant bath temperature of 40°C, average velocities ranged from 100 to 3500 mm s −1 and SRRs ranged from 5 to 100%.…”

“…The texturing density, defined as the ratio of the area covered by the textures to the total surface area, is considered to be a parameter which is less influential on friction than others . Several studies disclose that the optimal value is between 5% and 20% and is very often lower than 10%.…”