Study On Design And Friction Properties Of Circular-concave-and-spherical-convex Compound Texture

The circular concave texture is widely used but its improvement in friction reduction and wear resistance is still a difficult problem in tribology.Since the spherical convex texture has excellent hydrodynamic lubrication performance,if the spherical convex is utilized to generate second dynamic pressure in the circular concave,it is possible to further improve the tribological performance of the circular concave texture.Therefore,a novel texture —spherical-convex-and-circular-concave compound texture is proposed and its hydrodynamic lubrication model is established.The laser milling process,the tribological performance and related mechanisms under full and starved lubrication is studied.The geometry and distribution of the compound texture are designed,and in order to compare with the circular concave texture,the spherical convex height,bottom diameter,position and the circular concave depth are defined as the key research variables.On this basis,the hydrodynamic lubrication model of the compound texture is established based on Reynolds equation.The model is solved by the finite difference method and the over-relaxation iteration method.The simulation program is written and the iteration parameters are optimized.The compound texture is fabricated by laser milling.It is noteworthy that the final morphology is unpredictable in the laser processing because of the uneven material removal.As a result,the effect of laser scanning path,single pulse energy,spot spacing and processing times on textured depth and morphology are analyzed,and the processing parameters to achieve uniform material removal are obtain.These processing parameters are suitable for fabrication of compound texture with different spherical convex,and the obtained sectional profile is basically consistent with the design.Under full lubrication,the influence of spherical convex on the hydrodynamic lubrication performance of circular concave texture is studied theoretically and the results are verified by pin-on-disc experiments.The simulation results indicated that the spherical concave can enhance the inlet suction and generate second hydrodynamic lubrication in the circular concave,and thus generate larger load-bearing capacity.With the increasing of spherical convex height,bottom diameter or the decreasing of spherical convex eccentric distance,the load-bearing capacity is further enhanced under the optimized circular concave depth.The experimental results showed that the influence of the spherical convex shape is consistent with the simulation.However,compound texture with spherical convex close to the divergent region is worse in friction reduction,which is different from the simulation.The possible reason is that the inertial effect is neglected in model.The friction coefficient of compound texture is 29.1% lower than that of circular concave texture with optimal depth.The effect of spherical convex under starved lubrication is studied.In this case,the lubricating film is smaller and the wear caused by solid contact is existed.The experimental results showed that under optimal concave depth,the influence of spherical convex height,bottom diameter and position is basically consistent with the influence under full lubrication,meaning that the hydrodynamic lubrication effect is still dominant.Comparing to the circular concave texture with optimal depth,the improvement in friction reduction can reach 41%.The friction and wear may be increased when the spherical convex height or eccentric distance is smaller.The possible reason is that metal abrasive particles are easily brought back to the contact interface by the lubricating fluid.Under oil and grease lubrication,the maximum rotation speed corresponding to the friction coefficient rising is larger for the compound texture.The possible reason is that the spherical convex can increase the adhesion of oil or grease.