Research On The Sound Field Analysis And Design Of Fluid Polishing System Assisted By Focused Ultrasonic Vibration

At present,there were some damages in the processing of optical parts,which need to be polished and repaired.There were some problems in the method of repairing optical parts by abrasive flow polishing,such as low machining accuracy,limited by the shape of workpiece material and so on..Ultrasonic vibration assisted jet polishing could not process aspheric micro parts.Ultrasonic vibration was on the surface of workpiece or tool head,which resulted in the limited shape of workpiece.Based on the design and optimization of ultrasonic vibration assisted fluid polishing system,the effects of ultrasonic frequency and amplitude on abrasive velocity were analyzed.The sound field of the vibrating spherical shell was calculated.The sound pressure field of the polishing system was simulated and its structural parameters were optimized.In addition,the flow field characteristics of ultrasonic vibration assisted fluid polishing system were analyzed.Finally,the structure design and load characteristics of the new ultrasonic vibration assisted fluid polishing system were studied.The sound pressure measurement system was built to measure the sound field.The experimental results verified the removal effect of the ultrasonic vibration assisted fluid polishing system on the workpiece.The optimal machining target distance was determinedThe mechanism of material removal in ultrasonic vibration polishing of single abrasive was studied,and the velocity of single abrasive was analyzed with ultrasonic vibration parameters.In addition,the law of the transverse distribution of the sound pressure axis and focal plane of the focused ultrasonic vibration spherical shell under different ultrasonic frequencies and amplitudes was analyzed.When the frequency is fixed,the radius of the opening aperture of the spherical shell increases,the sound pressure of the main lobe near the focal spot increases,the transverse width decreases.In the near field,the amplitude of sound pressure changes sharply,but the attenuation of sound pressure changes slowly in the far field.With the increase of the frequency,the amplitude of the acoustic pressure field increases gradually,but the increase of the frequency does not affect the shape and range of the focal region.Simulation analysis of acoustic pressure field of focused ultrasonic vibration assisted polishing system by COMSOL.The spherical shell model of focused ultrasonic vibration with different structures was established.The influences of the matching layer on the front sleeve and the inner wall of the conical nozzle,the ultrasonic frequency and the taper of the conical nozzle on the sound pressure field of the spherical shell system were analyzed.The structure parameters of the system were optimized.The maximum sound pressure of ultrasonic vibration spherical shell in water appears at 90 mm of sound pressure axis.The sound pressure field in the water gradually converges in the focus area in the form of spherical wave.The focal spot size is an ellipse with a long axis of 10 mm and a short axis of 2 mm.Add sound-absorbing material to the inner wall of the front sleeve and cone nozzle of the polishing system.After the matching layer is set on the inner wall of the front sleeve,the sound pressure field is basically unchanged.When the matching layer is set on the inner wall of the conical nozzle,the sound pressure field becomes larger as a whole.The flow field of focused ultrasonic vibration assisted fluid polishing was simulated by finite element method.The acoustic module was used to calculate the dynamic sound pressure field of focused ultrasonic vibration system.When the fluid acts on the focused ultrasonic vibration system,the sound pressure field inside the system becomes larger as a whole.However,due to the existence of fluid,there is no obvious convergence of the dynamic sound pressure field at the focus.Secondly,with the increase of ultrasonic amplitude,the fluid velocity at the conical nozzle of the focused ultrasonic vibration system also increases,but the velocity inside the polishing system has little change.When the distance between the shell nozzle and the workpiece surface is smaller,the fluid velocity is larger.On the contrary,the velocity of the center of the workpiece surface is the smallest,and the two sides gradually increase,concave velocity distribution is formed.The distance h between the nozzle and the workpiece surface is 2 mm.Finally,focused ultrasonic vibration assisted fluid polishing system was designed and fabricated.The working principle of polishing system was analyzed.In addition,the frequency impedance characteristic of polishing system was analyzed by impedance analyzer.The impedance characteristics of the polishing system in different coupling environment were compared.The acoustic field characteristics of the focused ultrasonic vibration assisted polishing system were verified by the probe hydrophone measurement system,and the acoustic field was measured.The experimental results verified the removal effect of the focused ultrasonic vibration system on the workpiece.When the target distance L=80mm,the focused ultrasonic energy is the most concentrated.Plastic removal is the main way to abrasive impacting the surface of workpiece assisted by focused ultrasonic vibration.Plastic deformation occurs in the machining area of the workpiece center.The depth of the circular pit is up to25.86μm,and lateral uplift appears at the edge of the pit.