Theoretical Research And Device Design For Two-dimensional Ultrasonic Vibration-assisted Grinding

Hard and brittle materials like ceramics and composites have excellent properties,such as high strength,toughness,abrasion resistance and high-temperature resistance,are widely used in aerospace,optics,electronics and other fields.Since there are many machining defects such as large cutting force,high cutting heat and poor surface appearance,traditional machining method is very difficult to meet the demand of precision machining.By introducing elliptical ultrasonic vibration,two-dimensional ultrasonic vibration-assisted Machining greatly compensates for the deficiency of the traditional machining method,and gradually becomes the research hotspot in hard and brittle materials machining.At present,the application of ultrasonic vibration-assisted machining devices in grinding is not yet mature,especially the grinding equipment which makes workpiece vibrated elliptically,there are defects such as large structure size,difficulty of accurate presetting operating frequency and fixed nodes.In order to solve these problems,this thesis focuses on the study of two-dimensional ultrasonic vibration-assisted machining device which apply vibrations to workpiece.The main research contents are as following:Firstly,based on one-dimensional ultrasonic vibration-assisted grinding,the principle,type and machining advantages of two-dimensional ultrasonic vibrationassisted grinding were set forth.For face grinding and circumferential surface grinding,considering the track overlapping effect of adjacent abrasive particles,models for movement trajectory of the abrasive particles relative to the workpiece and material removal rate were founded from kinematics and dynamics respectively.And material removal mechanism and machining characteristics of two-dimensional ultrasonic vibration-assisted grinding which works on workpiece were studied.Secondly,based on the mechanism of two-dimensional ultrasonic vibrationassisted grinding,the structure of grinding device for elliptical vibration of workpiece was determined,the conditions for generation of elliptical vibration were analyzed,the structures and dimensions of each component were designed,emphatically introduced the structural design of longitudinal composite transducer whose front cover was a quarter-wave composite amplitude horn.The effects of structural size on resonant frequency of the composite horn were studied by using numerical simulation method,besides,the optimal impedance matching scheme of device and the influence of force load on electro-acoustic efficiency were discussed.Thirdly,based on theoretical design,the parameterized models of partial and overall structure of grinding device were established,whereafter,the sizes of the designed grinding device were optimized,and modal and harmonic response analyses were carried out by using piezoelectric coupling analysis method.The FEM analysis was used to obtain the relationship between the structure sizes of object stage(extended length and side length),transducers and the vibration characteristics(resonant frequency,node-section position,the maximum stress and amplitude),and optimized the sizes.After optimization,the error between the resonant frequency of the device and the theoretical design frequency is as low as 0.24%,and the amplitude is as high as 16.7μm.The effects of support pedestals,bolts and pre-tightening force were discussed,and the rationality of the analysis using a simplified model was verified.Finally,according to the optimal device model,the grinding device was machined,and the two-dimensional ultrasonic vibration-assisted grinding system and the test platform were built to test the vibration characteristics of device.The test results were consistent with the simulation results,and experiments were conducted to study the influence of force load on resonant frequency and impedance.The experimental results show that the device has excellent performance.