Study On Grinding Of Inner Surface Of Ultra-slender Tube Using Fe₃O₄/ZrO₂ Composite Magnetorheological Fluid

Ultra-slender tube is widely used in medical,aviation,aerospace fields.As an important component for transport of gas or liquid,there is a high requirement for the smoothness of its inner surface because a lower roughness value of the inner surface of the ultra-slender can not only improve the boundary conditions of fluid movement,reducing the frictional resistance coefficient and frictional resistance along the way,and reducing unnecessary energy loss,but also maintain the stability of fluid transportation.Therefore,it is of great significance to improve the smoothness of the inner surface of the ultra-slender tube,that is,to reduce the roughness value of the inner surface,to ensure the normal and safe operation of the equipment.Magnetorheological fluid is a suspension composed of free and loose magnetic particle,which is easily controlled by magnetic field and has strong processing flexibility,so it is very suitable for grinding slender tubes,but this processing has higher requirements for grinding capacity of magnetorheological fluid itself and the selection and optimization of grinding process parameters.Therefore,in this paper,“Study on Grinding of Inner Surface of Ultra-slender Tube Using Fe₃O₄/ZrO₂ Composite Magnetorheological Fluid”are proposed.Firstly,high-performance composite magnetorheological fluid was prepared by the self-designed two-step preparation method,that is,first nano-ZrO₂ abrasives with good dispersion was prepared,then high-performance Fe₃O₄/ZrO₂ composite magnetorheological fluid was prepared by high-energy ball milling.Secondly,mechanism of magnetorheological effect of composite magnetorheological fluid was analized.Model for shear stress of the composite magnetorheological fluid was established after in-depth study of the micromechanical model based on field-induced dipole theory,in addition,the grinding mechanism of the composite magnetorheological fluid was deeply analyzed.Finally,the high-quality internal surface of slender tube can be efficiently processed by Fe₃O₄/ZrO₂ composite magnetorheological fluid under the control of grinding process parameters.The main work and achievements are as follows:Aiming at the dispersion of nano-abrasion particles,the actual adsorption layer structure of surfactant on the surface of nano-abrasion particle was studied from a new perspective,surfactant content have a great influence on the dispersion stability of nanoparticle suspension,in this paper,surfactant content for optimal dispersion stability can be determined from the critical micellar concentration of surfactant,which is determined from multilayer adsorption isotherm from the constructed Langmuir2-SCA isotherm equation of multilayer adsorption of surfactant.It can be concluded from the simulated and experimental study on multilayer adsorption of surfactant on surface of abrasive particles that the prepared suspension of ZrO₂ abrasive particles has optimal dispersion stability,more stable friction coefficient and better friction performance when addition amounts of CTAB are 1mmol·L^-1.In order to improve the grinding capacity of Fe₃O₄/ZrO₂ composite magnetorheological fluid itself and improve the distribution uniformity and adhesion strength of abrasive particles on the surface of magnetic particles.Therefore,firstly,the relationship between the maximμm overlap of ZrO₂ nanoparticle and Fe₃O₄ particle and self-rotation angular velocity of ball mill tank was deduced to predict the interfacial bonding strength of Fe₃O₄/ZrO₂ composite magnetic particles by constructing motion diagram of the high-energy ball mill and analyzing the motion law of the grinding ball.Secondly,the influences of speed of the ball mill on the coefficient of thermal expansion,residual stress,interfacial bonding strength,magnetic properties and mechanical properties of the composite magnetic particles were deeply studied to determine optimal speed of the ball mill.Thirdly,the influences of addition amounts of ZrO₂on the friction coefficient,hardness and magnetic properties of magnetic abrasives were deeply studied in order to determine the optimal addition amounts of ZrO₂.Finally,the effect of volμme fraction of Fe₃O₄ magnetic particles on shear yield stress of composite magnetorheological fluid was studied.The results showed that Fe₃O₄/ZrO₂composite magnetic particles have low coefficient of thermal expansion,the minimμm residual radial tensile stress,the maximμm interfacial bonding strength,relatively stable friction coefficient,the maximμm hardness of 9.72 Gpa,and the lowest specific saturation magnetization of 13 emu/g under the condition that speed of the ball mill is150r/min.The friction coefficient of Fe₃O₄/ZrO₂ composites is the most stable,its hardness reaches the maximμm of 10.01Gpa,and its specific saturation magnetization is 14.52 emu/g when content of ZrO₂ is 2.13%under the action of CTAB.Magnetorheological fluid with both high shear yield stress and good fluidity can be prepared when the volμme fraction of Fe₃O₄magnetic particles is 14%.Magnetorheological grinding is a complex process involving multiple parameters.In order to fully analyze the effects of process parameters and their interactions on the grinding state of slender tube,firstly,the process parameters that have important influences on grinding effect of magnetorheological fluid were determined according to the constructed mathematic model of material removal rate on shear stress,and then the effects of the process parameters and their interactions on material removal rate（MRR）and the surface roughness（Sq）were studied.The surface roughness value of workpiece ground by composite magnetorheological fluid decreased from 4.121μm to3.164μm,which is decreased by 23.22%.Due to the contradiction problem of the optimal combination of each evaluation index,the optimization problem of multiple evaluation indexes is transformed into the optimization problem of single evaluation index of grey correlation degree by using grey correlation analysis.The obtained material removal rate is 0.0610μm/min,surface roughness value is 3.161μm,and grey correlation degree（GRG）is the highest,that is 0.6739 under the optimal process conditions that the speed of slender tube is 210r/min,the magnetic induction intensity is 96.07m T,the feed speed of magnetic poles is 3.33mm/r from the analysis of the effect plot of grey correlation degree,the above MRR and Sq values are increased by 42.71%and 32.74%than the obtained those values under the optimal process conditions that the obtained process parameters from the analysis of their each effect plot.Therefore,grey correlation analysis can be used to solve the coordination problem of each evaluation index.