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Towards industrial implementation of laser surface texturing as a tool for enhancing wear resistance and friction reduction on sliding surfaces

Authors:
  • Genetoo Inc.

Abstract

Energy losses due to friction and wear of sliding surfaces and other tribological contacts account for 23 % of the world's energy consumption [1]. This figure justifies the need for technologies capable of mitigating friction and wear. Accurate laser surface texturing of micro-metric sized features on sliding surfaces have shown a significant decrease of friction coefficients, while improving the lifetime of the pieces due to an increased wear resistance [2,3]. However, there are few constraints that may act as a barrier for this technology to be implemented in industry. These are partly related to the cost of the equipment, as the required quality of the surface features usually implies the use of expensive ultra-short pulsed laser sources. In addition, laser surface texturing speed may result in excessively long processing times. In this work, we first demonstrate the feasibility of using a cost-effective sub-nanosecond (ns) near-infrared (NIR) fibre laser source for the creation of different surface textures, which show friction reduction and an increased wear resistance. The surface pattern consists of arrays of micrometric-sized dimples and slots, with controlled depths and widths in the range of a few tens of micrometers. The resulting laser-textured surfaces show the required high-quality finishing, practically free of recast and molten redeposited material. Secondly, a 5-axes and a 4-axes laser systems, designed and built at Oxford Lasers, are respectively employed to demonstrate the scalability of the process to real components beyond flat surfaces. Different methods capable of creating the required features on pistons and on the inner surface of cylindrically-shaped pieces are presented. Dedicated tribological assays were carried out on test specimens, confirming a reduction on coefficient of friction (COF) of about 25 %, along with an increased wear resistance, which is quantified in terms of a significant reduction in the wear track widths of about 50 %.
Towards industrial implementation of laser surface texturing as a tool for enhancing wear
resistance and friction reduction on sliding surfaces
D. Arnaldo del Cerro1, E. Pelletier1, D. Karnakis1, A. Cunha2, K. Juste3
1- Oxford Lasers Ltd., Unit 8, Moorbrook Park, Didcot, Oxon OX11 7HP, UK
2- SENAI Innovation Institute for Laser Processing, Rua Arno Waldemar Dohler, 308, Santo Antônio, Joinville, Santa Catarina, Brazil
3- SENAI Innovation Institute in Surface Engineering, Av. José Cândido da Silveira, 2000, Horto, Belo Horizonte, Minas Gerais, Brazil
Corresponding author: daniel.arnaldo@oxfordlasers.com
Energy losses due to friction and wear of sliding surfaces and other tribological contacts account for 23 % of the
world’s energy consumption [1]. This figure justifies the need for technologies capable of mitigating friction and
wear. Accurate laser surface texturing of micro-metric sized features on sliding surfaces have shown a significant
decrease of friction coefficients, while improving the lifetime of the pieces due to an increased wear resistance
[2,3]. However, there are few constraints that may act as a barrier for this technology to be implemented in
industry. These are partly related to the cost of the equipment, as the required quality of the surface features
usually implies the use of expensive ultra-short pulsed laser sources. In addition, laser surface texturing speed
may result in excessively long processing times.
In this work, we first demonstrate the feasibility of using a cost-effective sub-nanosecond (ns) near-infrared
(NIR) fibre laser source for the creation of different surface textures, which show friction reduction and an
increased wear resistance. The surface pattern consists of arrays of micrometric-sized dimples and slots, with
controlled depths and widths in the range of a few tens of micrometers. The resulting laser-textured surfaces
show the required high-quality finishing, practically free of recast and molten redeposited material. Secondly, a
5-axes and a 4-axes laser systems, designed and built at Oxford Lasers, are respectively employed to
demonstrate the scalability of the process to real components beyond flat surfaces. Different methods capable
of creating the required features on pistons and on the inner surface of cylindrically-shaped pieces are
presented. Dedicated tribological assays were carried out on test specimens, confirming a reduction on
coefficient of friction (COF) of about 25 %, along with an increased wear resistance, which is quantified in terms
of a significant reduction in the wear track widths of about 50 %.
[1] K. Holmberg and A. Erdemir (2017) Influence of tribology on global energy consumption, costs and emissions, Friction, vol. 5, pp. 263-
284
[2] S.-C. Vlădescu, A.V. Olver, I.G. Pegg, T. Reddyhoff (2016) Combined friction and wear reduction in a reciprocating contact through laser
surface texturing, Wear, vol. 358-359, pp. 51-61
[3] J. Schneider, D. Braun, C. Greiner (2017) Laser Textured Surfaces for Mixed Lubrication: Influence of Aspect Ratio, Textured Area and
Dimple Arrangement, Lubricants, vol. 5(3), pp. 32-46.
The authors would like to acknowledge partial financial support from Innovate UK under grant No 102713
The authors would like to acknowledge partial financial support from SENAI-SESI-SEBRAE in the scope of the Innovation for the Industry Call
ResearchGate has not been able to resolve any citations for this publication.
Article
Full-text available
Unidirectional sliding experiments with polished and laser textured steel surfaces were carried out to investigate the effects of different textured area densities, aspect ratios and dimple arrangements. The system was lubricated with Polyalphaolefin (PAO) at 100 °C and the contact pressure was 3 MPa. For measuring Stribeck curves, the sliding speed was controlled between 40 and 2000 mm/s. The textured area density was varied between 5% and 30%, with the lowest friction values found for 10%. Aspect ratios ranging from 0.02 to 0.2 were investigated and for 0.1 the lowest friction values were measured. The dimple arrangements tested were cubic, hexagonal and a random distribution for a textured area density of 10% and an aspect ratio of 0.1. Our results demonstrate that the dimple arrangement does affect friction values, hinting to the fact that individual texture elements do influence each other. The optimum dimple arrangement was found in a hexagonal packing. This systematic variation of these three key texturing parameters for the morphological texturing of a tribological surface with dimples will allow a strategic choice of texturing parameters. This makes the most of the tremendous potential that laser surface texturing has for reducing friction forces and thereby CO2 emissions.
Article
The aim of this study is to gain insights into the interactions between laser-textured surface pockets and friction and wear behaviour of an automotive piston-liner pairing. To do this, a recently developed, reciprocating, test apparatus was used to conduct wear tests under highly loaded conditions. Fused silica specimens with a range of pocket geometries were rubbed against a convex steel pad and the resulting friction and wear data were compared with those from a non-textured specimen. Contact conditions were set to remove the influence of initial surface roughness on texture behaviour. These tests showed that, as the specimen become worn and surface roughness increases, the contact progresses further into the mixed and boundary regime. This leads to a significant improvement in the relative performance of the textured specimens, showing reductions in friction of up to 70%, compared with the non-texture case. This is consistent with previous results that have shown texture to have the effect of boosting film thickness in the mixed lubrication regime. Surface texture was also shown to reduce the volume of wear, by up to 69% (corresponding to a change in wear coefficient from 2.67e−4 to 0.81e−4[mm3/N·m]). Another, important, finding is that both friction and wear reduce monotonically as the sum of the pocket volumes along the stroke increases. This may aid texture design, since it means that individual pocket width and depth values can largely be ignored, so long as the overall volume is maximised. The only exception to this trend is when the pockets are larger than the contact area. In this case, friction increases due to a collapse of the lubricant film, while wear reduction remains unaffected - a discrepancy which may suggest that pockets reduce wear and friction via separate mechanisms
  • K Holmberg
  • A Erdemir
K. Holmberg and A. Erdemir (2017) Influence of tribology on global energy consumption, costs and emissions, Friction, vol. 5, pp. 263-284