On The Mechanism Of Ultrasonic ELID Composite Internal Grinding ZTA Nano Composite Ceramics

Nano composite ceramics is becoming a class of critical material in the national economy and the cutting-edge science and technology fields with its excellent mechanical properties,stable chemical properties and low microscopic defect sensitivity.However,nano composite ceramics in application requires a very high shape dimension accuracy and surface integrity,which is difficult to be processed,and especially it is difficult to achieve high accuracy,high efficiency and high reliability processing.In this paper,the ultrasonic vibration technology with high precision and efficiency as the main feature and the ELID(electrolytic in-process dressing)grinding technology with ultra precision mirror as the main feature are compounded,ZTA nano composite ceramics is studied as research object,the relationships between ultrasonic vibration parameters,grinding parameters and ELID parameters,and the influence of them on the grinding process,and the influence of ultrasonic ELID grinding process parameters on workpiece surface texture are studied,in order to reveal the mechanism of ultrasonic ELID grinding nano composite ceramics,and to provide support for improving the high efficiency mirror machining theory and technology of hard brittle materials.First of all,an experimental platform of the ultrasonic ELID composite grinding ZTA nano ceramics is built,and the main work include: Based on the wave theory and ANSYS finite element modal analysis method,the ultrasonic vibration system is designed;after the anode and the cathode of the electrolytic device are designed respectively,they are integrated into the ELID device;according to the principle of EDM,and through parameters adjustment of each stage of EDM dressing,the cast iron bonded diamond grinding wheel is put into EDM dressing test,the result shows that the initial cylindrical error of the grinding wheel is reduced to about 2?m by 32?m with most grinding grains protruding cast iron bond surface,so as to meet the precision requirements of the grinding wheel.Based on the electrochemical principles of growth and removal of the oxide film in the ultrasonic ELID grinding wheel,the geometrical parameters analysis of the axial ultrasonic vibration assisted grinding and the analysis of a single grinding grain cuttingpath,a thickness model of the oxide film in the ultrasonic ELID composite grinding wheel is established.The model simulation results are as follows: During the course of approximate linear growth of the oxide film thickness,the larger the electrode gap is,the smaller the oxide film thickness is,and the slower the forming speed is;the larger the size of the abrasive grains is,the larger the oxide film thickness is,and the faster the forming speed is;the greater the duty cycle is,the greater the oxide film thickness is,and the faster the forming speed is.During the course of nonlinear growth of the oxide film thickness,the higher the ultrasonic frequency is,the faster the film forming speed is,and the greater the oxide film thickness at the balance is.Single factor tests are carried out and drawn forth the influencing mechanism of power supply voltage,electric pulse width and pulse interval,electrode gap,grinding wheel speed and ultrasonic vibration on the thickness,forming speed and surface morphology of the oxide film at the pre-truing stage of the ultrasonic ELID grinding;the influence of various parameters on the oxide film state is analyzed qualitatively by changing the wheel speed,workpiece speed,grinding depth and abrasive particle size at the dynamic grinding stage;a power-off polishing grinding test and a ultrasonic vibration added power-off polishing grinding test are conducted,compared,and reveal the influencing mechanism of ultrasonic vibration on the polishing property of the oxide film.Finally,to verify the oxide film thickness model of the grinding wheel,the thickness values of the measuring points in the process of the pre-truing and dynamic grinding of the grinding wheel are collected in the field,at the same time,and the thickness values of the measuring points are calculated theoretically,the results show that the correlations of Boltzmann function fitting in both stages are very good,the trend of thickness measurement is similar to that of its theoretical prediction,which reflecting that the oxide film thickness grows over time,the growth rate decreases over time,thus the rationality of the oxide film thickness model is confirmed.Based on the kinematic analysis of an abrasive particle and the construction of dynamic effective abrasive grain number model of the ultrasonic ELID composite grinding,an average non deformation abrasive debris thickness model of the ultrasonic ELID composite grinding is established.Materials removing test of the ultrasonic ELID composite grinding ZTA nano ceramics is conducted,and through the study of therelationship between grinding depth and grinding force,workpiece surface roughness and surface morphology,the relationship between grinding depth and grinding effect is changed into the relationship between non deformation abrasive debris thickness and grinding effect.By analyzing the variation law of the grinding force and surface roughness and the SEM(scanning electron microscope)photographs,the transition condition between brittleness and plasticity for the removal of ZTA nano ceramic material is determined to be 1.565?m of average non deformation abrasive debris thickness.the surface roughness model is established based on the average non deformation abrasive debris thickness model,the correctness of the surface roughness model is confirmed by the model simulation and surface roughness test,thus the rationality of the average non deformation abrasive debris thickness model and the transition condition between brittleness and plasticity for the removal of ZTA nano ceramic material is confirmed.Finally,the surface forming mechanism for the ultrasonic ELID composite grinding is revealed by abrasive grain cutting track simulation analysis and surface forming experiment.To sum up the above,the rationality of the prediction model of the oxide film thickness of the ultrasonic ELID composite grinding wheel is confirmed,which lays a certain theoretical foundation for revealing the process of ultrasonic ELID grinding nano composite ceramics;and establishment of the critical cutting depth of transition between brittleness and plasticity for the removal of ZTA nano ceramic material by ultrasonic ELID grinding provides a basis for further improving the surface quality of nano composite ceramics.