Experimental And Theoretical Investigation Into Electrorheological Polishing

1. IntroductionEntering for the 21st century, the global economy is booming and people's lifeis improved every day. With the development of the optical communicationtechnology, medical treatment and image technology, it is urgent necessary of massof micro-optical parts. The micro aspheric glass lenses are a very representativeexample. The aspheric glass lenses have the characteristic of proofreading imageerror, improving image quality, expanding the field of view and so on. Meanwhile,it makes optical system improving resolution, the structure simplified, the weightlightened. But the present processing method of aspheric glass lens is near netmolding, namely precision casting molding, which needs aspheric glass lens diehave the nice surface. However, it is very difficult or incapable of micro asphericglass lens processing for traditional polishing technology. The paper develops theresearch of the electrorheological(ER) polishing technology for the case, whichmakes use of ER fluid of ER effect and mixes some micro fine abrasive material,then supplies high voltage direct current (DC) and through the polishing flexibleabrasive head of rotary processes the micro aspheric glass lens.2. Research of the experiment of the ER effectER effect has been approved by many academicians, but ER fluids havedifferent performance parameter and appraisal index for the different dispersiblephase and the continuous phase. The paper develops a system for experimentassembly for the self-research of ER fluid. Figure 1 is the diagrammatic system andfig.2 is the entity of the experiment assembly.The experiment assembly system is made up of the high voltage DC power, theFig.1 Experiment assembly principle of ER effect Fig.2 Entity of ER effect testtrapezoidal experiment table, the trapezoidal pole, crocodile clip and someconducting wires. The silicone oil (continuous phase) and the starch (dispersiblephase) makes up ER fluids, which are supplied high voltage DC power and formsfiber chain fabric, such as fig.3.The relative strength of the resistance shear abilityof the fiber chain decides ER fluids performance. For the case, the paper developsthe resistance shear force experimental structure——experimental assembly of theoutflow angle, such as fig.4.Fig.3 Micro phenomena of ER effect Fig.4 Diagram of outflow angle testThe outflow angle is the largest declining angle which ER fluids effuse fromthe experimental table, on the condition of experiment table leaned and it issupplied electric field. The works principle is that one angle and the other angle aremutually perpendicular, namely the outflow angle ∠ 1 and the angle ∠ 2 fromprotractor is equal. So it is convenient of measuring outflow angle from theprotractor and may know the experiment data on the relative strengthen of the EReffect.The silicone oil qua continuous phase and the starch qua the dispersible phasemake up ER fluids. The paper has carried on the experiment with three kinds ofdispersible phases density 10%,20%,30%, respectively. The experimentalconclusion is that steady state voltage of ER fluids and the pole spacing becomelinear relations change under three kinds of the dispersible phase density and withthe reduction dispersible phase density on the same pole spacing, need voltage risesstep by step, that is, the experimental curve rate of slope augments gradually.The silicone oil and simethicone qua continuous phase individually and thestarch as dispersible phase do the above same experiment. Experimental conclusion— when voltage is steady, voltage and spacing are linear relations, regardless of thesilicone oil or simethicone qua continuous phase respectively and the experimentcurve rate of slope of the smaller dispersible phase density of ER fluids is lagerthan the higher under the same conditions, such is the uniform with the aboveconclusion.Through developing and designing the experiment assembly system of the EReffect, the paper investigates the self-researched ER fluid of characteristic andindividually analyses the simethcone and the silicone oil qua continuous phase ERfluid of the experimental data. Meanwhile, ER fluid of ER effect of relativestrength and electric field strength are changed linearly on the same electric fieldstrength condition, which supplies powerful basis for the further research of the ERpolishing experiment.3. Experimental research of ER polishingThe paper establishes the ER polishing experimental assembly system which isbased on numerical control milling-drilling machine. The experimental assemblysystem is mostly made up of the join frame, suspending contract frame, pole frame,the rotary pole, insulation join nut, insulation gasket, carbon brush and so on. Fig.5is the entity of the experiment table, fig.6 is the design of experiment assemblysystem.Under the electric field supplied, ER polishing fluids which are made upself-research ER fluid and micro fine abrasive material forms a homoplasticallysoft abrasive head on the head of the tool pole. Through the tool pole revolution,homoplastically soft abrasive head may finish processing the micro region andfig.7 is the principle of ER polishing.Al2O3 qua the micro fine abrasive material, the experiment polishes theFig.5 Entity of experiment assembly(1-join frame;2-suspending contact frame;3-pole frame;4-rotary pole;5-insulation join nut;6-insulationgasket;7-carbone brush)Fig.6 Design of experiment assembly system(1-insulation base;2-bolt;3-nut;4-gasket;5-cam-ring chuck;6-suspending join frame;7-insulation nut(containing insulation gasket);8-rotary pole;9-work;10-T form base;11-inner hex bolts;12-gasket;13-nut;14-join frame;15-carbone brush;16-fixed screw;17-pole frame)tungsten carbide (WC) cemented-carbide. It is known that the work surfaceroughness from Ra=24.21nm (such as fig.8) before polishing to Ra=9.84nm (suchas fig.9) after polishing by measuring the work surface roughness with Wyko.1234567The technology of ERpolishing remarkably improvesthe processed surface roughnessnumerical value from thepolishing before and aftersurface roughness. So it iscompletely feasible of applyingthe technology of ER polishinginto the field of precisionfinishing. To seek the bestworking processing parameter,the paper does orthogonal test and the single factor test on the ER polishing,respectively. From the orthogonal test, the primary and secondary factor ofaffecting the technology of ER polishing is polishing processing time, the rotaryspeed of the pole, the source of voltage and the micro fine abrasive material density.The single factor test provides the approximately perfect numerical value for eachfactor—— polishing processing time 30 minutes, the rotary speed of the pole2000rpm, supply voltage 400V and the micro fine abrasive material density 5%.Fig.8 Surface roughness before polishing Fig.9 Surface roughness after polishingThe experimental results show that it is feasible of applying the technology ofER polishing into the precision processing field, but needs further research yet.4. Principle research of ER polishingThere are the dispersible phrase particles and the micro fine abrasive materialparticles in the ER polishing fluids. Without the electric field supplying the ERpolishing fluids, there are the force of molecule and the heat motion among theFig.7 Principle of ER fluid-assisted(1-direction of rotary pole;2-"homoplastically soft abrasive head";3-tool pole;4-direction of rotary tool;5-work pole)13245molecules. However, the whole body system is supplied with the DC field andforms ER effect and particles are forced with the electrostatic field force and thedielectrophoresis force among the particles. The relative strength betweenelectrostatic field forceand dielectrophoresisforce decides therigidity ofhomoplastically softabrasive head, at lastaffect the efficiency ofmachining and theeffect on polishing.Fig.10 is the micromodel.The paper analyses some factors of affecting ER effect, such as the type ofelectric field, the relative permittivity, the size and shape of particles, temperatureand the dispersible phase density and so on, and simulates and calculates theelectrostatic force and the dielectrophoresis force by establishment mathematicalmodel among the particles. Some important expressions as follows:The expression of the particles electrostatic force:eRFpp0f 121212 23πεε=? (1)The expression of the particles polarized momentum:2[1(/4)(/4)](1/4)33333330dRdRdEdRpepepapapfepepapapep ββπεεεβ?= + (2)2[1(/4)(/4)](1/4)33333330dRdRdEdRpapapepepfapapepepap ββπεεεβ?= + (3)The expression of the particles dielectrophoresis force:32FD EP = π4 ε0εfβdpgradE (4)The expression of the electric field strength between the tool rotary pole and thework:Fig.10 Micro model of ER fluid-assisted polishing(1-work pole;2-high DC source;3-micro fine abrasive;4-rotary tool pole;5-ERpolishing fluid;6-ER particle)214536The expression of the work surface charge density:ρ = C ?εep?El (6)Simulating calculation results show the primary force which affects ER effect isthe electrostatic force in the ER polishing fluids about three micro fine abrasivematerial, and the dieletrophoresis force may be basically ignore. The dielectricconstant of the micro fine abrasive materials contributes a fat lot to the forceamong the particles. Such is favorable that the scholars analyses thoroughly theremoval principle of ER polishing in the future.5. ConclusionThe paper study subject is associative the project on the outstanding youthfulresearch plan in Jilin Province, which is the research of ER polishing microaspheric mould, and the contract number is 20050121. The paper carries throughthe key experiment research and the theory analysis of ER polishing machining.The thesis of primary work and conclusion as follows:Firstly, the thesis has elucidated the development condition of ER fluid at homeand abroad and researches the mechanics on ER fluid forming ER effect and ERfluid as the intelligent material applies in the field of engineering, and thenintroduces the research condition of ER polishing and exists in some problems atpresent.Secondly, the paper researches and develops the proving test system of thephenomenon on ER effect. The system is made up of the GYU-10/5 high voltageDC power supply, the transmission electric line, the copper pole, the base, theconstant force device, the metering installing, the insulation tape, the screw and thecrocodile clip and so on, which may do proving experiment on the ER effect ofself-researched ER fluid.Thirdly, the thesis develops the ER polishing experimental assembly system,and carries through the orthogonal test and the single factor test on ER polishing,and experiment results show that the processing parameter which affects primarilyER polishing machining takes turn the polishing time, the speed of the rotary pole,the supply voltage and the micro fine abrasive material density, the best level offour factors is ordinal for 30min, 2000rpm, 400V and 5%.Fourthly, the paper applies the theory of electric field strength, Coulomb's Lawand the principle among particles forcing into ER polishing machining andanalyses the simple removal mechanics and draws some laws on the particlesforcing in the ER polishing fluid, based on Gauss's Law, the thesis provides thebasic principle of the surface charge density of confirmation and the calculationexpression on it. The calculation may be better near real value. Such is basic for thefurther ER polishing technology study.