Study On Structural Design Of Longitudinal-torsional Composite Ultrasonic Transducer And Cutting Process Experiment

Composites and ceramics materials are widely used in engineering because of their excellent properties such as high hardness,high strength,high wear resistance,high corrosion resistance and high temperature resistance.However,it is difficult or even impossible to process this kind of brittle-hard materials using conventional processing methods due to their poor toughness and brittleness,which limits their application in industry.Compared with conventional processing methods,ultrasonic processing technique has the advantages of effectively reducing cutting force,improving processing quality and reducing tool wear.However,the conventional ultrasonic machining is difficult to be applied in practice due to its low processing efficiency and low processing quality.The ultrasonic machining combined with longitudinal and torsional vibration modes is better for tool retraction during cutting,so it can avoid edge chipping and hence improve the efficiency and processing accuracy of the hard-brittle materials processing.This work investigates into the longitudinal-torsional rotary ultrasonic processing technology,by reviewing the literature,analyzing the practical applications of longitudinal-torsional rotary ultrasonic machining,and finally developing an appropriate longitudinal-torsional ultrasonic transducer.Experiments on zirconia ceramics have been carried out to investigate the mechanism of the longitudinal-torsional ultrasonic cutting,by analyzing the cutting force,surface quality and the critical cutting depth of brittle-plastic transition.A numerical model is obtained by using the three-dimensional finite element optimization technology based on the vibration conversion mode theory.The numerical results show that the resonance frequency is 26.73 KHz,the longitudinal-torsional ratio is 37.28%,and the longitudinal amplitude of the tool tip is 2.43μm.The measured results show that the transducer has good impedance performance.The resonance frequency is 27.646 k Hz,the longitudinal amplitude is 4μm,the torsional amplitude is 1.33μm,and the longitudinal-torsional ratio is 33.33%.They are consistent with the numerical analysis and can satisfy the processing requirements.A cutting force model is established based on the kinematic trajectory and the relationship between average cutting force and process parameters based on the mechanism of longitudinal-torsional ultrasonic cutting.It is found that the depth of cut is directly related to the brittle-plastic transition of the material.Under the condition of quasi-equilibrium,an analytic model representing the proportional relationship between the average cutting force and the crack length of the material is established,and the relationship of the process parameters and the surface crack length of the material is obtained indirectly.The combination of rough processing and plastic removal finishing of hard-brittle materials is also proposed.It is found that the longitudinal-torsional ultrasonic machining can effectively reduce the cutting force and reduce the wear of the tool,through comparing the single-force force measurement of cutting force and analyzing the ultrasonic vibration energy,feed rate,depth of cut and spindle sp eed.The effects of processing parameters on the surface roughness of zirconia ceramics,and the variation of surface roughness of the milling tool and the grinding tool are compared.Experiments of ordinary cutting,longitudinal vibration processing and longitudinal-torsional vibration processing have been carried out to compare and analyze the cutting depth scratching.It is found that improving the ultrasonic vibration energy within about 50% can improve the critical cutting depth of the brittle-plastic transformation of the material,and the torsional composite vibration can produce deeper critical cutting depth than the longitudinal vibration.The critical cutting depths of the brittle-plastic transition of ordinary cutting,longitudinal vibration processing and longitudinal-torsional vibration processing increase with the feed rate,and the longitudinal vibration can produce deeper critical cutting depth than the longitudinal-torsional vibration.