Surface texturing has emerged in the last decade as a viable option of surface engineering resulting in significant improvement in load capacity, wear resistance, friction coefficient etc. of tribological mechanical components. Various techniques can be employed for surface texturing but Laser Surface Texturing (LST) is probably the most advanced so far. LST produces a very large number of micro-dimples on the surface and each of these micro-dimples can serve either as a micro-hydrodynamic bearing in cases of full or mixed lubrication, a micro-reservoir for lubricant in cases of starved lubrication conditions, or a micro-trap for wear debris in either lubricated or dry sliding. The present paper reviews the current effort being made world wide on surface texturing in general and on laser surface texturing in particular. It presents the state of the art in LST and the potential of this technology in various lubricated applications like mechanical seals, piston rings and thrust bearings. The paper also describes some fundamental on going research around the world with LST.

State of the art in Laser Surface Texturing

Surface texturing has emerged in the last decade as a viable option of surface engineering resulting in significant improvement in load capacity, wear resistance, friction coefficient etc. of tribological mechanical components. Various techniques can be employed for surface texturing but Laser Surface Texturing (LST) is probably the most advanced so far. LST produces a very large number of micro-dimples on the surface and each of these micro- dimples can serve either as a micro-hydrodynamic bearing in cases of full or mixed lubrication, a micro-reservoir for lubricant in cases of starved lubrication conditions, or a micro-trap for wear debris in either lubricated or dry sliding. The paper reviews the current effort being made world wide on laser surface texturing in particular. It presents the state of the art in LST and the potential of this technology in various lubricated applications like mechanical seals, piston rings, thrust bearings, magnetic recording etc. The paper also describes some fundamental on-going research around the world with LST.

State of the Art in Laser Surface Texturing

The effect of laser texturing of SiC surface on the critical load for the transition of water lubrication mode from hydrodynamic to mixed

The friction characteristic of a journal bearing with dimpled bushings manufactured using the machining and the chemical etching techniques is investigated. A series of experimental results is presented to examine the effect of dimples on the Stribeck curve. Load, oil type, dimple size, depth and shape are varied to explore their influence on the friction characteristics. It is shown that with proper dimensions of dimples, the friction performance of journal bearings can be improved, particularly for light oils. The results reveal that in mixed lubrication regime, the so-called secondary lubrication effect in the dimpled area is the main mechanism responsible for improvement of performance. Experimental results also indicate that a bushing with etched dimples over the entire circumference offer a better frictional performance than a bushing with dimples etched on half of its circumference.

An Experimental Investigation of Dimple Effect on the Stribeck Curve of Journal Bearings

Dimples shape and distribution effect on characteristics of Stribeck curve

A model of a secondary hydrodynamic lubrication mechanism, which is called micro-pool or micro-plasto hydrodynamic lubrication, has been developed. It shows that, with sufficiently high viscosity and sliding speed, the lubricant trapped in the micro-pools between the tool and workpiece can be drawn into the interface. The friction force is either increased or decreased, depending on the viscosity and sliding speed. Without bulk stretching, the product of the lubricant viscosity and sliding velocity can be used as an index to indicate whether or not micro-pool lubrication will occur. Stretching the workpiece may make a strong influence not only on the thickness of the permeating film but also on the asperity contact area.

A theoretical model of micro-pool lubrication in metal forming

A porous medium model is basically a macroscopic description of the fluid behavior and is considered more appropriate to the mixed lubrication regime. The present work has successfully combined the flow factor method, porous medium model and continuum percolation theory to investigate the flow phenomena in the mixed lubrication regime. Not only the lubricant flow can be solved but also the anisotropoic percolation threshold can be obtained. Instead of the flow factor which is singular near h=o, the lubricant flux iTself is considered. A new definition of the pressure flow factor which is more appropriate to the mixed lubrication realm is suggested

A Study on Flow Phenomena in Mixed Lubrication Regime by Porous Medium Model

A comprehensive approach for computing the lubricant flow as functions of the roughness orientation is presented. By using a mapping function, a periodic, anisotropic surface is transformed into an isotropic one. The transformed isotropic roughness has only one characteristic wavelength, so that a double scale analysis based on this wavelength of roughness can be developed to calculate the flow factors introduced in the average Reynolds equation. In addition, the Bhushan number instead of the conventional Peklenik number is used to describe the surface property more clearly

Sy-Wei Lo

Papers

A theoretical model of micro-pool lubrication in metal forming

A Study on Flow Phenomena in Mixed Lubrication Regime by Porous Medium Model

On the Effects of Roughness Orientation—A Mapping and Double Scale Analysis of Flow Factors