Study On The Longitudinal-torsional Composite Ultrasonic Milling System Of Carbon/Silicon Carbide And Machining Stability

With the increasing demand of C/SiC materials in the national defense,aircraft and automatic,the requirements for parts machining accuracy,surface quality and machining efficiency become increasingly harsh.The traditional machining methods are difficult to meet the requirements of machining C/SiC materials.Because of the advantages in decreasing the cutting force,improving the surface quality of workpiece and extending tool life effectively,ultrasonic processing technology is considered as the most effective methods for machining C/SiC materials.According to the characteristics of the workpiece,the idea of combining longitudinal-torsional composite ultrasonic vibration with traditional milling is put forward for seeking the high quality and efficiency precision machining method.In this paper,the key technologies of longitudinal-torsional composite ultrasonic milling system are researched.The longitudinal-torsional composite ultrasonic vibration system and contactless power transmission system are developed.Meanwhile,the processing stability of longitudinal-torsional composite ultrasonic milling system is discussed.At last,the experiments of longitudinal-torsional composite ultrasonic milling of C/SiC materials and traditional milling of C/Si C materials are carried out,and the performances and effects of of longitudinal-torsional composite ultrasonic milling C/SiC materials are also discussed.The main research contents and achievements are as follows:(1)For the application defect of modal superposition type longitudinal-torsional composite ultrasonic transducer,the design ideas that the degenerate node is constructed on the longitudinal-torsional resonant frequency transducer,by using characteristics of the ring slot structure with longitudinal vibration coupling and torsional vibration isolation,are put forward.At last,the modal analysis of the ultrasonic transducer are researched by finite element software ANSYS,and the ideas are verified.(2)By comparing the apparent elastic theory,one-dimensional vibration theory and finite element method,the length-diameter ratio can be used as the basis to determine the application scope of one-dimensional vibration theory.Based on one-dimensionalvibration theory,the frequency equation of longitudinal vibration sandwich ultrasonic transducer with the rear bolt is derived by using equivalent circuit method.On this basis,the sandwich ultrasonic transducer based on longitudinal-torsional coupled vibration is developed,and the vibration performances of the transducer are optimized and tested by using the finite element software ANSYS and impedance analyzer.(3)Based on the transfer matrix method,the longitudinal-torsional resonance frequency equations of three composite stepped ultrasonic horns with the shape like cone,exponent and catenary.At the same time,the simultaneous resonance of the longitudinal-torsional composite vibration in the horn is realized by reasonable choosing different section length of the horn.On this basis,Stress states of the round bar when the longitudinal vibration and torsional vibration travel in the round bar are studied,and the patch type longitudinal torsional ultrasonic vibration system based on the31 d effect is put forward.(4)Based on the wave transmission theory,the propagation characteristics of modal converter with slits are analyzed,and the frequency equation of the modal converter is modified.The longitudinal-torsional composite ultrasonic horn with slits is developed.In order to expand the longitudinal-torsional composite ultrasonic vibration realization form,there kinds of longitudinal-torsional modal converter with the shape like holes,oblique beams and chutes are deveopped.(5)Based on the kinematics synthesis principle,the cutting trajectory feature and cutting characteristics of separaed longitudinal-torsional composite ultrasonic milling are analysed,and the essential characteristics of reducing cutting force,improving the surface quality and extending the tool life are elucidated.Then,based on the structural dynamics theory,considering the effects of longitudinal-torsional composite ultrasonic vibration,the dynamic model and the stability region analytical model of the separated longitudinal-torsional composite ultrasonic milling are constructed.The stability lobe diagram of cutting system is obtained,by using the software MATLAB 7.1.Finally,the influence of processing parameters and modal parameters on the machining system stability was analyzed.(6)Based on the developed longitudinal-torsional composite ultrasonic milling system,the machining experiment of C/SiC materials is carried.The surface quality andmicro morphology of workpiece under different milling parameters are observed,and the machining mechanism of C/SiC materials in the longitudinal-torsional composite ultrasonic milling is revealed.The comparison experiment of traditional minlling and longitudinal-torsional composite ultrasonic milling of C/SiC materials are carried out.The results showed that the longitudinal torsional ultrasonic milling can significantly reduce the cutting force,improve the surface quality of the workpiece and prolong the service life of the cutter.