Research On The Forming Mechanism And Surface Properties Of Micro-textured Surfaces Fabricated By Ultrasonic Vibration Assisted Turning

The surface texturing technology is an important way to improve surface performance to prepare for the functional surfaces which can meet different needs in various areas.It has gained more and more attention and research recent years.Though many methods have been applied to fabricate the micro-textured surface,the development of texturing technology with high efficiency,low cost and suitable for large-scale industrial application is still the current research focus and development trend.The technology of one-dimensional ultrasonic vibration assisted turning combines the traditional turning and the external ultrasonic vibration.By applying regular and controllable ultrasonic vibration in the cutting process to change the cutting path of the tool,and matching reasonable processing parameters,it can simply,directly,quickly and efficiently fabricate the dimpled micro-textures on the workpiece surface,which provides a potential texturing method for the preparation of functional surface.However,there are few researches on the one-dimensional ultrasonic vibration assisted turning for fabricating the micro-textured surface at present,and the relevant theories and analysis are not perfect.Therefore,this surface texturing technology is worthy of further research and development.In this paper,two kinds of one-dimensional ultrasonic vibration assisted turning(ultrasonic vibration in the feed direction and in the cutting depth direction)are studied systematically from three aspects of theoretical analysis,simulation prediction and experimental verification.The main research contents and conclusions are as follows.(1)According to the movement characteristics of one-dimensional ultrasonic vibration assisted turning,the kinematics analysis of surface texturing processing was carried out.For the ultrasonic vibration assisted turning in the feed direction,the equations of feed rate and phase difference of cutting trajectory were established,and the state of adjacent cutting trajectory of cutting edge under different processing parameters was analyzed.Based on the characteristics of ultrasonic vibration assisted turning in the cutting depth direction,the geometric motion models of intermittent cutting and continuous cutting were established respectively.The key factors that affect the shape,size and distribution of micro dimples were found,the change rules of profile shape and size of the dimples in different cross states between the flank face and the cutting trace were clarified,and the similarities and differences between the micro-textured cylinder surface and the end face were compared and analyzed.The results show that the micro-dimples on the cylinder surface fabricated by the ultrasonic vibration assisted turning have the same size,shape and distribution state,while the micro-dimples on the end face have the characteristics of multi-scale,multi shape and variable distribution density.(2)Based on the principle of geometric contour remapping,simulation model of micro-textured surface topography in ultrasonic vibration assisted turning were established through the establishment of the simplified model of tool geometry,the transformation of space coordinate system,the establishment of vibration cutting motion equation and the discretization of space and time,etc.Matlab algorithm was used to realize the input of processing parameters and the output of surface topography in the simulation process.The prediction and analysis of micro-textured surface topography under different vibration machining parameters were completed.The results show that the simulation model can provide effective reference for the analysis and prediction of textured surface features and the optimization of processing parameters.(3)The experimental platform of ultrasonic vibration assisted turning in feed direction was built,and the influence of processing parameters on the surface textures was studied combined with the simulation results.The results show that only by selecting the appropriate processing parameters,including the feed rate and amplitude with little difference,can the dimpled texture surface with regular topography be machined by the ultrasonic vibration assisted turning in the feed direction.(4)Based on the kinematic analysis of the ultrasonic vibration assisted turning in the cutting depth direction,the influence of processing parameters of intermittent cutting on the surface topography characteristics of micro-texture and the dimple profile size were studied systematically from the perspective of simulation prediction.Through the combination of simulation analysis and experimental verification,the influences of tool parameters and vibration cutting parameters on the micro-dimpled cylinder surface were systematically analyzed,and the optimal scheme of processing parameters was determined.Based on the analysis results of the continuous micro-textured cylinder surface,the simulation prediction and experimental research of the machining characteristics,shape,size,and distribution of the micro-textures on the end face were carried out.The results show that compared with the ultrasonic vibration assisted turning in the feed direction,the ultrasonic vibration assisted turning in the cutting depth direction is a more simple and efficient method for the surface texturing,which has higher accuracy and better controllability of the size,shape and distribution of micro-dimples.(5)The properties of micro-textured surface fabricated by ultrasonic vibration assisted turning in the cutting depth direction were studied.The influence and its mechanism of micro-textures formed by three kinds of clearance angle on the wettability of cylinder surface were analysed.The surface topography,surface roughness,surface microstructure and surface friction and wear characteristics of the polished,micro grooved and micro-dimpled surfaces were respectively studied.The mechanism of friction and wear reduction of micro-dimples on the surface under the condition of low speed and light load oil lubrication friction was studied.The micro-dimpled surface with better friction properties and its corresponding processing parameters were obtained.The results show that the shape and distribution of micro-dimples determine the spreading difficulty of the surface water droplets along the feed direction,which leads to the different hydrophobicity of the three micro-dimpled surfaces processed by different clearance angles.The micro-dimpled surface has better friction performance than the polished surface and the micro-grooved surface.In the friction process,the micro-dimple mainly plays the role of storing oil and containing wear debris,so as to reduce the degree of surface wear and make the surface have a smaller friction coefficient.In addition,the distribution density of micro-dimples also has a certain influence on the surface friction performance.Choosing the surface with larger distribution density of micro-dimples is more conducive to improving the surface friction performance under the condition of oil lubrication friction.