Fundamental Theories And Enabling Technologies In Mechanical Lapping Of Micro Diamond Tools With Round Noses

The micro structured arrays,which have multitudinous excellent characteristics,are widely applied in numerous high-tech fields,such as biomedicine,environmental protection,photovoltaic energy,optical system,flexible skin,virtual reality,information storage,national defense and military industry.At present,fabricatation of the large-scale surface covered with micro structured arrays is mainly depended on the ultra precision machining,and thus micro diamond tools with round noses are essential in the machining process.However,because of the insufficient precision and excessive wear of the micro diamond tool,the shape accuracy and roughness of the microstructure are unsatisfactory,and burrs are prone to formation at the microstructure edges.Especially for the large-size surface with microstructured arrays,the integrity and consistency are substantial decline with the tool wear,resulting in a sharp degradation of the design function.Therefore,in order to obtain high-precision and wear-resistant micro diamond tools with round noses,investigations on the design methods of crystal plane combination and mechanical lapping technologies of micro diamond tool are performed in this work.Firstly,an anisotropic mathematical model of diamond friction is established at micro and nano scale based on the analysis of the friction phenomenon during the mechanical lapping process of diamond crystal,in which mechanical and physical properties,plastic deformation,interface adhesion and surface texture state of the diamond crystal are comprehensively considered.The internal mechanism of diamond friction anisotropy is well revealed by the friction model,whose correctness and reliability are verified by molecular dynamics(MD)simulations and nano friction experiments.The simulation and experimental results indicate that diamond friction coefficient has a significant scale effect,which is caused by the interface adhesion and the accumulation effect of debris atoms at micro and nano scale.Based on the asestablished model and the results of MD simulations,material removal mechanism under the action of friction is explored in the process of diamond mechanical lapping.The results suggest that the anisotropic phase transition,dislocation,local shear deformation and graphitization in the subsurface induced by the frictional force are the main origions for the anisotropy of material removal rate during diamond mechanical lapping process.Secondly,a cutting edge strength model during mechanical lapping is established for micro diamond tools with round noses with different crystal plane combinations,and the corresponding verification experiments of mechanical lapping for the strength model are performed.The internal relationships between the waviness and sharpness of micro diamond tool cutting edge and the cutting edge strength are analyzed according to the model and experimental results.And further,a design criteria for controlling the cutting edge waviness and sharpness are proposed for different application requirements for micro diamond tools.The theoretical and experimental results inllustrate that the cutting edge strength of micro diamond tools with different crystal plane combinations appears an anisotropic characteristic in varying degrees.The cutting edge sharpness and waviness are respecitively dependent on the strength values and spatial distribution of cutting edge belong to the flank face.The uniform distribution of cutting edge strength on the flank face is conducive to obtain an excellent waviness,while the larger cutting edge strength on the flank face is conducive to obtain a fine cutting edge sharpness.Thirdly,on the base of cutting edge strength distribution model established for micro diamond tool mechanical lapping process,considering the influence of chip flow direction and minimum cutting thickness,a modified model of cutting edge strength is further derived for the machining process.Based on the modified model,the magnitude and spatial distribution characteristics of cutting edge strength during micro diamond tool cutting process are analyzed.Then,the wear resistance and tool nose wear morphology of the micro diamond tools with different crystal plane combinations are predicted.Further a design method of micro diamond tool is proposed,which is beneficial to improve the tool wear resistance.The accuracy of cutting edge strength distribution model for cutting process and the reliability of tool wear predictions are verified by the microstructured array machining experiments.Theoritical and experimental results prove that micro diamond tool wear resistance is determined by the tool nose strength magnitude and spatial distribution,in terms of the wear resistance,the descending order of micro diamond tools as follows: A_γ{110}Aα{110}> A_γ{110}Aα{100}>A_γ{100}Aα{110}>A_γ{100} Aα{100}.Finally,considering the effects of static force components,including friction,abrasive scratching force and cutting force,and dynamic force components,including debris impact and lapping disc impact,a force model of micro diamond tool during mechanical lapping is established and verified by experiments.The contribution of each component to the lapping force and the mechanical stress in the lapping region are analyzed based on the force model.Then,a process method for lapping high-precision micro diamond cutting tools with round noses is proposed,and a series of mechanical lapping experiments are conducted on to verify the effectiveness of the new method proposed in this work.The results support that a high-precision and wear-resistant micro diamond tool with a round nose is efficiently and stably fabricated with the method,which provides a pivotal enabling technology supporting for the high-precision fabrication of functional surface covered with microstructured arrays.