| With the rapid development of new diffcult-to-finish metal materials,the required surface quality is getting higher.How to process these materials has become a research hotspot of ultra precision machining technology.The electrolysis compounded shear-thickening polishing(ESTP)method,based on the primary principle of shear thickening polishing(STP)and the electrochemical polishing(ECP),is proposed to realize the high efficiency,high quality and low-cost process for difficult-to-finsih materials.In this paper,the main contents of the ESTP method are as follows:The ESTP principle and processing characteristics were described and the main influence parameters of ESTP processing were analyzed,ESTP experimental platform was established,which includes the key devices such as multi-axis linkage that drive device of workpiece maximum spindle speed is 3000 rpm and polishing slurry of rotating platform spindle maximum speed is 400 rpm and pulse electrolysis power supply,which pulse electrolysis power supply frequency range is 0-250 KHz,duty cycle is 0-100%,unipolar square is wave,pulse voltage range is 0-150 V,pulse current range is 0-20 A,power output peak is 500 W.The preparation method and characteristics of electrolysis compounded shear-thickening polishing slurry(ESTPS)were studied.The composition and properties of the electrolyte based fluid were determined as water: phosphoric acid: sulfuric acid: glycerol = 5:3:1:1,the viscosity was 0.004-0.007 Pa.s.Taking the the surface roughness Rz as evaluation index,the current density has the most significant effect on characteristics of electrolysis,followed by the power duty cycle,the power frequency.Adding abrasive grains to the fluid with polyhydroxy polymer as the dispersed phase and the deionized water mixed the electrolyte as the solvent.The electrolysis compounded shear-thickening polishing slurry was determined by dispersed phase and the solvent.The influence of key parameters including abrasive particles,the particle size,concentration on the rheological properties have been tested in rotary rheometer.It was found that the polishing slurry composition with 50% dispersed phase particles and 5-15μm particle size was best in shear thickening properties.Besides,polishing slurry contained Al2O3 has showed typical rheological properties.,which viscosity increases nearly 100 times when shear rate increases from 30 s-1 to 1000 s-1.The formula of the friction resistance and the pressure resistance in the ESTP process are deduced and the calculation formula of the mechanical model of the workpiece surface is obtained.On the basis of the empirical model of electrochemical polishing,the model of material removal in the polishing process was established.In addition,the synergistic mechanism of electrolytic oxidation and shear thickening of ESTP was discussed.When the current is 1.5A and the rotational speed reaches 100 rpm,the velocity of electrolytic oxidation generates passivation layer is nearly same as the removed velocity of the passivation layer.However,when the current is 2.5A and 3.5A,the rotational speed is 90 rpm,80 rpm matched to current respectively.The effects of current density,power duty cycle,polishing speed and abrasive concentration on the polishing efficiency and quality were analyzed by polishing experiment.The results show that the processing efficiency of ESTP is 4-5 times as STP,and the efficiency of ESTP is nearly equivalent to post-electrolytic shear thickening polishing method.After 20 minite’s processing,the 304 stainless steel surface roughness is reduced rapidly from Ra 315 nm to Ra 5 nm. |
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