| Friction and wear have always been the focus of research in the field of mechanical engineering.Reducing the friction coefficient of the surface of the friction pair has the important significance of improving the stability of the mechanical system and saving energy.The existing research shows that the special micro texture can reduce the friction coefficient of the friction pair surface.However,the existing processing technology has relatively high cost and poor flexibility in the preparation of microtexture,and it is difficult to meet the requirements for the preparation of multi scale surface microtexture.Therefore,this paper proposes a method to prepare the surface microtexture by selective laser melting of nanometer copper powder,and systematically studies the following aspects,which are summarized as follows:1.Using analytical model and numerical simulation research on thermal characteristics of laser nano copper powder layer.Based on the radiative transfer equation,an equivalent radiative transfer model for laser induced co pper nano powders is established.And the energy distribution of the copper nano powder was obtained by using the Two-Flux method.On this basis,body heat source model of nanometer powder layer absorption laser induced was established,and the influence and law of the parameters of the properties of the copper nano powder layer(the thickness of the powder layer and the extinction coefficient)on the distribution profile of the body heat source were analyzed.A finite element model for the temperature field of copper powder is established.The width of laser single track is predicted by temperature field simulation.The results show that the width of the single channel increases linearly with the increase of laser power in a given laser power range,and the effect of the scanning speed on the width of the single channel is relatively small.2.Dispersion solution of copper nano powder was configured.And a single channel scanning,single layer scanning and multi-layer scanning test of the selective laser melting copper nanometer powder was carried out by using the self built test platform.The parameters range of stable single channel sintering and high quality plane sintering were determined,and the defect forms and the causes of the single channel scanning trajectory and the sintered surface were analyzed.The relationship between the thickness of copper layer and the surface quality and the number of scanning layers was obtained by multi-layer scanning test.The results show that the width of the single channel increases linearly with the increase of laser power in the reasonable test range,which proves the correctness of the simulation analysis,and the effect of the process parameters on the single channel height is less;the scanning distance has a great influence on the quality of the sintered surface,and the maximum thickness of the stable multilayer sintering is about 30?m.3.The supercharging characteristics of the micro texture on the lubricating liquid film are simulated and analyzed.Based on the simulation results,a square micro textured surface with aspect ratio of 0.2 was fabricated by selective laser melting of copper nano powders.Frictional performance tests were carried out to investigate the effect of working conditions,micro texture size and spacing on the friction reducing properties of micro texture.The results show that the friction reducing performance of a square convex micro texture surface with a size of 100 ?m × 100?m,a spacing of 200?m and a depth to width ratio of 0.2 is the best under the condition of load 20 N and relative motion velocity of 220mm/s,and the friction coefficient is reduced by 49% compared with the surface without the micro texture friction pair. |
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