Study On Mechanism Of Ultrasonic Assisted Grinding And Trepanning Process Of Hard And Brittle Materials

Hard and brittle materials have been widely used in many fields,such as aviation,aerospace and so on,because of its outstanding properties,including the high hardness,wear resistance and high temperature resistance.However,the properties of high hardness and brittleness lead to the poor cutting performance,which seriously limits its development.Lots of research results show that the technology of ultrasonic assisted grinding can reduce the cutting force,reduce tool wear and improve the material removal rate,which is the preferred method for machining the hard and brittle materials.Therefore,the mechanism and process of ultrasonic assisted grinding of hard and brittle materials need the further research.But through the research of domestic and foreign literatures,in the studies of ultrasonic assisted grinding of hard and brittle materials,all the grinding force models are relatively one-sided without considering the influence of abrasives on the transition fillet of the grinding wheel,and there are few reports on the study of the theoretical calculation of the diameter error and the edge chipping damage on the end face of the core rod during the ultrasonic assisted trepanning process.In order to solve the above problems,the kinematics analysis of single abrasive particle on the surface of the grinding wheel is carried out.By considering the influence of abrasives of the transition fillet,the grinding forces are calculated based on the situations of the normal and tangential ultrasonic vibration amplitudes and feedrates of the diamond grains in contact with the workpiece change with the penetration angle ?.Based on the impulse theory,the theory of indentation fracture mechanics and the material removal rate,the calculation formulas of the grinding forces produced by the diamond abrasives in the end face,lateral face and transition fillet surface of the grinding wheel are established,and the axial and feed direction grinding force models of ultrasonic assisted grinding are obtained finally.Secondly,the values of the coefficients K and Ks in the grinding force model are obtained though ultrasonic assisted grinding experiments,and the effects of the speed,amplitude,feedrate,cutting depth and radius of the transition fillet on the coefficients and the grinding force are studied,and the validity of the model is verified.Then,based on the crack propagation theory during the theory of indentation fracture mechanics,and with the use of the grinding force model established,the diameter error of the core rod during ultrasonic assisted trepanning is calculated theoretically,and the reliability of the calculation model is verified by experiments.During the experiments of the ultrasonic assisted trepanning,the influences of speed and feedrate on the diameter error of the core rod are studied,and the differences of the diameter error of the core rod between ultrasonic assisted grinding and conventional grinding with different speeds are contrasted.Finally,the morphologies of the end face of the core rods with different rotational speeds and different feedrates are observed,and the edge chipping damages of the end face of the core rods during the ultrasonic assisted grinding and conventional grinding are compared.Using the ratio of the undamaged area of the end face to the cross sectional area of the core rod,the influences of different variables on the severity of edge chipping damages of the end face of the core rod are studied quantitatively.