Mechanism And Experimental Study Of Dispersion Of Ultrasonic Cavitation Bubbles On Magnetorhe-ological Polishing Fluid

Aiming at the problem of particle sedimentation of magnetorheological polishing fluid during the preparation and storage of magnetorheological polishing fluid,this article summarizes the domestic and international research trends of magnetorheological polishing fluid and ultrasonic cavitation bubbles,based on the principle of energy conservation and numerical simulation methods.The bubbles and particles in the ultrasonic dispersion magnetorheological polishing fluid are simulated by dynamic simulation,and the ultrasonic parameters and the characteristics of the magnetorheological polishing fluid are studied.At the same time,drawing on the preparation process of the traditional magnetorheological polishing fluid,the ultrasonic-assisted mechanical preparation process is proposed,the observation experiment and the processing experiment research are carried out,and the influence of different parameters on the sedimentation and processing effect of the magnetorheological polishing fluid is analyzed and discussed.The details are shown as follows:（1）The average density of the selected magnetorheological polishing fluidρ=2238.37 kg?m³,and the viscosity coefficientμ=2.238kg/（m·s）.The liquid viscosity measured by the rheometer is 3.5271Pa?s,which is an order of magnitude with the calculated zero-field viscosityμ=2.238kg/（m·s）.The vibration characteristics of cavitation bubbles in the magnetorheological polishing fluid are obtained,and the radius of cavitation bubbles with different initial radii changes with time.The cavitation bubbles undergo larger expansion and compression and then continue to expand for many times with smaller cycles.And compression,and continue to repeat this vibration process.As the initial radius of the cavitation bubble increases,the amplitude of cavitation bubble expansion becomes smaller and the period of expansion and compression gradually becomes larger.As the ultrasonic frequency increases,the cavitation bubble radius ratio to its initial radius decreases inversely,and the vibration frequency of cavitation bubbles with an initial radius of 5μm is higher than that of cavitation bubbles with an initial radius of 10μm.As the sound pressure amplitude increases,the cavitation bubble radius changes significantly The increase,and the smaller the initial radius,the more obvious the change of cavitation bubble motion with the sound pressure amplitude;the effect of sound velocity on the change of cavitation bubble radius is small,and the effect of sound velocity can be ignored.（2）Obtain the secondary Bjerknes force model of a single particle to a single cavitation bubble in the magnetorheological polishing liquid,and analyze the change of the secondary Bjerknes force of the bubble acting on the particle with time through numerical simulation.The force of a single cavitation bubble on a single particle in the rheological polishing liquid is first slightly attracted,and then a strong repulsion and attraction quickly occur,and a cyclic attraction of repulsive attraction with a smaller and smaller force.The effect of different parameters on the secondary Bjerknes force is as follows:the force of a single cavitation bubble on particle 2（R₂=100μm,ρ_p=3120kg?m³）is significantly greater than particle 1（R₂=5μm,ρ_p=3500kg?m³）;With the increase of the initial radius of the cavitation bubble,the period of the force gradually increases.The ultrasonic frequency has little effect on the magnitude of the force,but with the increase of the ultrasonic frequency,the period of the force gradually increases Increase.The ultrasonic amplitude has little effect on the size of the force cycle,but as the ultrasonic amplitude increases,the size of the force increases significantly.Subsequently,the kinetic model of the particles in the magnetorheological polishing liquid was improved,and the particle speed firstly increased rapidly,and then stabilized and cyclically circulated,which indicated that the particle speed firstly increased rapidly,and then kept away from the bubble at a little changed speed.（3）According to the numerical simulation results and test requirements,the traditional mechanical stirring preparation of the magnetorheological polishing liquid is improved.The ultrasonic dispersion is used to prepare the magnetorheological polishing liquid.The selected variables are the ultrasonic power,the amplitude of the horn into the liquid and the ultrasonic time.Based on the central composite design and response surface method,the sedimentation rate test and data analysis were carried out.The single factor influencing the sedimentation rate of the magnetorheological polishing fluid from strong to weak in turn were:ultrasonic power>ultrasonic time>amplifier penetration depth.The interaction factors that influence the sedimentation rate of the magnetorheological polishing fluid from strong to weak are as follows:ultrasonic power+ultrasonic time>ultrasonic power+horn penetration depth>ultrasonic time+horn penetration depth.The ultrasonic power and ultrasonic time increase,and with the increase of the liquid depth of the horn,the sedimentation rate decreases first and then increases.It was also found that under the effect of 800W ultrasonic power,the temperature of the magnetorheological polishing fluid rose from the initial 16.3℃to 41.2℃,which had a certain effect on the stability of the magnetorheological polishing fluid.Compared with the traditional mechanical dispersion process,the magnetorheological polishing liquid prepared under the ultrasonic power of500W,the horn input depth of 30mm,and the ultrasonic time of 0.5min parameters can not only shorten the preparation time greatly,but also reduce the liquid sedimentation rate.The ultrasonic dispersion and mechanically prepared magnetorheological polishing fluid were used to process the outer surface of the aluminum tube and hydraulic spool.The roughness removal rate of the outer surface of the workpiece was compared to verify the processing effect and feasibility of the ultrasonically dispersed magnetorheological polishing fluid.