Surface Texture Construction Based On Multi-pass Laser Ablation And Laser Polishing

Surface texture is a special micro-structure existing on the surface of materials,which has a certain distribution law and specific morphology and can be obtained on the solid surface by some processing methods.Surface texturing of friction pairs has become an important method to improve the performance of friction pairs in the field of fluid lubrication.Due to the limitation of processing methods,the texture with uncontrollable bottom shape is the main research object at present.In recent years,the simulation research and experimental results show that some specific textures can be constructed by adjusting the process parameters in laser processing,but the experimental research on the formation mechanism and morphology influence law of textures is lacking.In order to fabricate the surface texture with controllable bottom shape,the influence of laser processing parameters on texture morphology was investigated by laser ablation and laser polishing.Specific work has been carried out as follows:Firstly,according to the working characteristics of nanosecond laser ablation,the influence of laser processing parameters on single-line ablation is studied.By laser ablation on 1060 aluminum alloy,linear pit combination,pit lattice combination and wire slot were processed by single factor variable method.The effects of laser power,scanning times and defocus on the texture of pits or wire slots were studied.The results show that the texture depth and opening width of pits and slots are different,which are determined by different control mechanisms There is a certain upper limit of energy accumulation in laser ablation texture morphology.This means that the transverse and longitudinal control of texture morphology can be realized by laser ablation,which provides reference value for the processing of texture with controllable bottom shape.Secondly,in order to initially construct the surface texture with wedge-shaped bottom shape,the single laser ablation is designed in combination,that is,multi-pass laser ablation is carried out,and the remelting distribution phenomenon during laser ablation is investigated.By machining linear pit offset group,pit lattice offset group and double-line overlap group,the effects of point overlap rate,line overlap rate and ablation times on texture morphology were studied.The results show that under the influence of laser energy overlap in different degrees,the depth of texture and the width of opening show different trends,which indicates that the remelting distribution of melt in the process of laser combined ablation is directional and selective.On this basis,the experimental process of laser ablation has been summarized,several groups of suitable laser processing parameters have been selected and optimized,and a wedge-like or near-inclined texture with shallow depth and not narrow width has been constructed,which verifies the energy accumulation and melt remelting distribution mechanism proposed in the laser ablation experiment.Then,the existing surface texture was finished by laser polishing on 718 alloy and 304 stainless steel,and the formation reason of moire effect,a special phenomenon of laser polishing,was investigated.The results show that the ripple produced by laser polishing(with a scale of tens of microns)is quite different from the distance between laser pulses(10microns);The amplitude of ripples produced by different laser energy is different,and the amplitude of ripples decreases with the decrease of laser energy Ripple wavelength has little change with laser energy and has certain stability.The research shows that the generation of ripple is a complex process involving the absorption of laser energy by materials,melt flow,evaporation of materials and even pulse timing,and its root lies in the difference of melt flow caused by laser polishing alternately acting on melt and high temperature solid.Finally,the laser polishing refinement strategy was introduced,and the surface texture array constructed by 1060 aluminum alloy smooth plate and multi-pass laser ablation was polished by laser.The influencing factors of laser polishing were analyzed,and the effect of laser polishing on texture morphology was studied.The results show that lower laser power and smaller scanning line spacing have better polishing effect;Under different energy,the scanning line spacing and scanning path affect the control mechanism of laser polishing,which leads to the directional distribution of melt in the process,and then affects the surface morphology After laser polishing the texture,the bulge decreases,the depth-diameter ratio decreases greatly,and the cross-sectional profile of the texture is optimized The transfer of materials in laser polishing is directional,and there is a correlation between the depth of texture and the height of outer protrusion after polishing.The shallower the texture,the more deposits on the outer side and the higher the height of corresponding protrusion.Laser polishing can't reduce the roughness of the array texture surface.With the increase of polishing power,the surface brightness decreases.It is considered that the regular small round holes produced by polishing absorb more incident light and affect the glossiness of the polished surface.The research results of this paper provide a certain experimental and theoretical basis for constructing surface texture with controllable bottom shape by laser processing,which has certain reference value for improving surface texture and friction pair shape.