Study On The Micro-characteristic Of Surface And Subsurface Of Nano-zirconia Ceramics In Ultrasonic Grinding

As a typical hard-brittle material,nano-zirconia ceramics are widely used in national defense and life because of their good physical and mechanical properties.Due to the high hardness and low toughness of the brittle material,the surface and subsurface of the workpiece can be easily damaged,affecting the surface quality and service life.Ultrasonic grinding is a kind of special processing method which combines ordinary grinding method with ultrasonic vibration.It has been widely used in ultra-precision machining of hard-brittle materials,because of its small grinding force,low grinding temperature,and can achieve good surface quality.This paper mainly studies three kinds of grinding methods,ordinary grinding,axial ultrasonic grinding and tangential ultrasonic grinding.In order to further study the microscopic characteristics of ultrasonic grinding on the surface and subsurface of nano-zirconia ceramics,the following work has been carried out:(1)According to the dynamic characteristics of ultrasonic grinding,a single abrasive grain was taken as the research object and the motion trajectory and force state of axial ultrasonic grinding and tangential ultrasonic grinding were systematically analyzed.The mathematical model of mechanics and motion trajectory of three grinding methods are established respectively.(2)The ordinary scratching,axial ultrasonography and tangential ultrasonic scratching test were performed respectively on the nano-zirconia ceramics.The influence of process parameters on three kinds of scratching force and scratching morphology were studied.The results show that the cutting depth has the greatest influence on the scratching force and the scratching morphology.With the increase of the cutting depth,the scratching force of the workpiece under three kinds of scratching forms increases significantly.The introduction of the ultrasonic vibration causes the normal direction of the workpiece is obviously reduced,the tangential force and the axial force have different trends due to the direction of the ultrasonic vibration.The axial ultrasonic scratching groove is the widest,followed by the ordinary scratching,and the tangential ultrasonic scratching groove is the narrowest.The bottom of the groove by tangential ultrasonic scratching is the least smooth,because of it has a large jump of the instantaneous depth of cutting.The proportion of the brittle fracture on the surface of ordinary scratching is the largest,and there have been large pieces of shedding.(3)According to the theory of indentation fracture mechanics,the relationship between the surface roughness and the depth of subsurface damage was analyzed.The subsurface damage depth models under three kinds of grinding methods are established,and the depth of processing parameters on subsurface damage is further studied.(4)The ordinary grinding,axial ultrasonic grinding and tangential ultrasonic grinding test were performed respectively on the nano-zirconia ceramics.The surface roughness and subsurface damage depth of the workpiece under different grinding conditions were studied and the influence of different process parameters on surface roughness and subsurface damage depth was also analyzed.The results show that with the increase of cutting depth,the surface roughness and the depth of subsurface damage are significantly increased.Compared with ordinary grinding,the surface roughness of axial ultrasonic grinding is reduced by about 20% to 35%,the subsurface crack depth decreased by about 60% to 75%.The surface roughness of tangential ultrasonic grinding reduced by about 10% to 20%,and the maximum subsurface crack depth decreased by about 10% to 20%.