Design And Characteristic Research Of Longitudinal-torsional Piezoelectric Ultrasonic Vibration System

Sapphire has been widely used in MEMS and other industrial fields due to its high hardness,good wear resistance and stable chemical properties.Ultrasonic grinding technology can effectively improve the surface quality and processing efficiency of the workpiece,which is the most common method of sapphire grinding processing at present.With the increasing requirements of sapphire processing,traditional one-dimensional ultrasonic grinding still has some problems,such as low processing efficiency,uncontrollable surface quality and serious tool wear.Therefore,it is necessary to find a more appropriate processing method to improve the grinding quality.The vibration modes such as longitudinal-bending compound,longitudinal-torsional compound and radial-bending compound of two-dimensional ultrasonic grinding show significant machining advantages due to high machining efficiency and good surface quality,and the research and development of two-dimensional ultrasonic grinding have a very broad prospect.Therefore,this paper proposes the method of longitudinal-torsional ultrasonic vibration to grind sapphire,and designs a longitudinal-torsional piezoelectric ultrasonic vibration system to improve the processing efficiency and surface quality,in order to cope with the increasingly complex processing requirements of sapphire.The research content of this paper can be divided into the following aspects:(1)Characteristics and application of ultrasonic machining technology are described,and the background and application of the ultrasonic assisted grinding technology are introduced,The research status of piezoelectric ultrasonic vibration system at home and abroad is summarized and the application and advantages of longitudinal-torsional composite vibration machining are introduced。(2)According to the one-dimensional vibration theory and the torsional vibration theory,the principle of torsional vibration of the longitudinal-torsional horn is analyzed.The design method of piezoelectric transducer is introduced,the piezoelectric equation and characteristic parameters of piezoelectric ceramics are discussed.The theoretical basis is provided for the structural design of the longitudinal-torsional piezoelectric ultrasonic vibration system.(3)Based on the ultrasonic frequency equation and resonant design principle,the ultrasonic transducer and the longitudinal torsional transducer of the longitudinal-torsional piezoelectric ultrasonic vibration system are designed and the material type is selected,the helical groove of longitudinal-torsional horn is designed and structural dimension parameters are obtained.The resonant frequency of the longitudinal-torsional horn is analyzed by finite element simulation,and the rationality of resonant design is verified.(4)Geometric model of the longitudinal-torsional piezoelectric ultrasonic transducer is established and the characteristic frequency and frequency domain are analyzed by the software of COMSOL Multiphysics.The results show that the natural frequency of the transducer is22.002 k Hz,which can produce good axial and tangential displacement amplitudes under the excitation frequency,and have good longitudinal torsional vibration performance.The displacement node and motion trajectory of the transducer are analyzed,and the correctness of the theoretical design is verified.(5)The impedance and amplitude of longitudinal-torsional piezoelectric ultrasonic vibration system are measured by using ultrasonic element analyzer and laser displacement sensor.Test results show that when the pre-tightening force is 21875N(pre-tightening torque is70Nm),the resonant frequency of longitudinal-torsional mode ultrasonic transducer is21.695 k Hz,which is 1.4% different from the result of simulation.The amplitude characteristics of the transducer are stable,the longitudinal and torsional amplitudes(peak-to-peak values)are7.5μm and 2.3μm,respectively,and the ratio of longitudinal-torsional amplitude is 0.31,which meets the requirements of ideal design and verifies the correctness of theoretical design and finite element simulation analysis.The temperature test of the longitudinal-torsional mode ultrasonic transducer is carried out.Rise of temperature of the transducer is caused by the dielectric loss and mechanical loss in the working state,the temperature of the output end of the amplitude transformer increases greatly,and the resonance frequency of the transducer decreases,which affects the output performance of the amplitude.