| Friction is closely related to the reliability,service life and energy consumption of mechanical components.Properly reduce friction can make the mechanical components work in good environment,prolong its service life and improve energy efficiency,which can significantly reduce the economic losses. Since the laser surface texturing (LST), as a new method to improve the tribological properties of surface,is emerging,it quickly attracts the attention of scholars at home and abroad.The optimal tribological performance can be got by design suitable textural topography and parameters.In order to get the optimal tribological performance of H13 die steel in its working condition,the paper combined theory,experiment and simulation to optimize the dimple parameter and research the lubrication mechanism.In theoretical research,the paper analyzed the principle of dimple to improve the lubrication state.The lubrication model of surface-to-surface contact pair was established on the base of Reynolds equation and the method of solving the equation was discussed.Then using the FLUENT,a kind of computational fluid dynamical software,to simulated the established model.The effect of dimple diameter,depth and density on the magnitude and distribution of the film was analyzed.The results showed that when the dimple diameter was 120μm,the the dimple depth of 13 μm can produce the best hydrodynamic lubrication effect,when the dimple’s diameter and depth were 100μm and 10μm respectively the optimal density of dimple was 13%.In the aspect of processing,the H13 die steel samples were processed by the semiconductor-pumped YAG laser device.Compared the two-dimensional dimple morphology obtained by two different methods under the same experimental condition.The result indicated that the quality of the dimple morphology obtained by "single pulse at the same point,interval more times"processing method was better than the quality obtained by continuous processing method.In terms of laser processing auxiliary process,the effects of auxiliary gases on the dimple quality were investigated.Nitrogen proved to be the best gas,using it as auxiliary gas,the hardness of the surface was greatly increased and the dimple morphology is the best.Laser parameters which affected the dimple parameters were as follows:the dimple diameter was mainly affected by the current,the depth was mainly affected by pulse numbers .repetitive frequency and defocusing amount also had some effect on dimple parameters.The best range of repetitive frequency was 1600Hz～2000Hz and the optimal defocusing amount was about 0.5mm.In the aspect of tribological experiment,Utilizing the Response Surface Analysis Method to design the experiments,then a series of contrast experiments were performed by the MMW-1A friction and wear tester,at last the experimental data were dealed with by the software Design-Expert.Experimental results showed that dimple can indeed reduce the friction coefficient. Among the dimple parameters, diameter had the maximum effect on the friction coefficient,the density had the minimum effect.The interaction effect between dimple parameters also had some effect on friction coefficient,but the effect was lower than the single parameter.During the data processing, mathematical model of friction coefficient related to each of dimple parameters was developed.The accuracy of the model was investigated by validation tests and the error range was within 5%.Based on the model the paper optimized the dimple parameters comprehensively.The optimal combination of dimple parameters are as follows:diameter was 180μm,depth was 14μm,density was 12%.The friction coefficient of textured sample with the optimal dimple parameters was 0.083,compared with the untextured sample it was reduced by nearly three times. |
PDF Full Text Request