Research On Mechanism And Machining Quality Of Engineering Ceramics By Longitudinal-torsional Composite Ultrasonic Vibration Assisted Helical Grinding For Hole Making

The hard and brittle materials such as engineering ceramics have excellent physical and chemical properties which is high hardness,high temperature resistance,wear resistance,corrosion resistance.It is a critical support for the development of science and technology.It plays an important role in the development of emerging industries such as aerospace,nation defense and military,and new generation of information technology.However,due to its high hardness and low fracture toughness,it is difficult to achieve high efficiency and high quality machining by traditional grinding methods.Rotary ultrasonic machining is widely recognized as an effective method for processing hard and brittle materials,but there are some problems such as poor surface quality and edge chipping,which restrict the extensive application of hard and brittle materials.On the basis of summarizing the research status of rotary ultrasonic machining and hole-making technology,this paper gives full consideration to the machining advantages of ultrasonic vibration of different vibration modes and helical hole making technology,using grinding instead of drilling,and puts forward the method of longitudinaltorsional composite ultrasonic vibration assisted helical grinding for hole making.Zirconia engineering ceramics was chosen as the research object,the kinematic analysis was carried out.And the material removal mechanism was analyzed based on the indentation fracture mechanics theory and surface morphology at the bottom of the blind hole.On this basis,the grinding force model was established,and its machining quality was studied,which provides a reference for the realization of efficient and precise machining of hard and brittle materials.The main research contents are as follows:(1)Established the trajectory equation of single abrasive particle by longitudinaltorsional composite ultrasonic vibration assisted helical grinding machining.The movement trajectory was simulated by MATLAB software,the movement characteristics were analyzed,and the influence law of each process parameter on the processing process was explored,which lays the foundation for the subsequent clarification of material removal mechanism,the establishment of grinding force model and the matching of appropriate process parameters.(2)Based on the theory of indentation fracture mechanics,combined with the analytical model of contact stress field of the interaction between abrasive particles and materials,the nucleation and propagation law of the interaction between abrasive particles and materials were analyzed,and the influence of ultrasonic vibration on the crack system and the critical depth of the ductile-brittle transition of materials was further analyzed.At the same time,the surface morphology of the hole bottom was observed by scanning electron microscopy,and it was found that under the action of ultrasonic vibration,the change of grinding groove depth during the interaction stage between abrasive particles and materials presents "deep in the middle,shallow on both sides",and the depth gradually decreased from the middle to both sides.The material removal modes include brittle fracture removal,ductile mode,and brittle fracture is the dominating mode of material removal.The main failure mode of brittle fracture is transgranular fracture.(3)On the basis of kinematics analysis and the material removal mechanism analysis,the grinding force model of the longitudinal-torsional composite ultrasonic vibration assisted helical grinding for hole making was established.The grinding force test platform was build to conduct verification experiment.The results verified the validity of the model.On this basis,according to the prediction results of grinding force model,the influence of process parameters on grinding force was analyzed.(4)Experiments were carried out to study the machining quality of the longitudinaltorsional composite ultrasonic vibration assisted helical grinding for hole making machining.The surface roughness of the hole wall and of the bottom of the blind hole,and the hole entrance chipping was chosen as quality appraisal target system.The formation mechanism of hole wall surface,the hole bottom surface of the blind hole,the hole entrance chipping was analyzed.Then,the influence law and degree of process parameters(such as ultrasonic amplitude,pitch,feedrate and spindle speed)on machining quality were analyzed.In addition,compared with the longitudinal ultrasonic vibration and the ordinary helical grinding machining,the results show that the longitudinal-torsional ultrasonic vibration assisted helical grinding is more beneficial to improve the machining quality.It has the value of providing reference for engineering application.