Research On Metal Surface Electrolysis And Plasma Polishing And Process

Electrolysis and plasma polishing is a “green” non-traditional machining that canefficiently polish metal workpieces and provide high-quality surface by removal effectof the gas layer discharge between the polishing solution and the workpiece. Itspolishing solution is salt solution with low concentration, which can be repeatedly usedby adding salt, so, with broad application prospect, it can solve the problems thatmechancal polishing is not fit for the workpieces with complex shapes and chemicalpolishing and electrolytic polishing are generally not environmentally friendly.The reason for microcosmic planarization and the polishing mechanism areexpounded on. Based on the gas discharge theory, influence of composition of thepolishing solution on the polishing effect is studied. It is found that electrolysis andplasma polishing is a dynamic process consisting of gas discharge and chemicalreactions and a precondition of the polishing is that the removal rate of the discharge isfaster than the production rate of the reactions. Curves of voltage and current with timeand volt-ampere characteristic curves dropping a workpiece into the polishing solutionin various ways are obtained by experiments and analyses to choose the best way todrop. Shape dimension, roughness, corrosion resistance, micromorphology, surfacechemical composition and microhardness of stainless steel before and after polishing arestudied by using relevant instruments. The experiment results show the ideal effects ofelectrolysis and plasma polishing and validate the mechanism to a certain extent.During the analyses on heat transfer process of material removal and energy gainsof the surface of metal workpieces in electrolysis and plasma polishing, it is discoveredthat the workpiece’s surface heat flux density has a great effect on the material removalrate and the gains come mainly from electron-bombardment. According to the materialremoval mechanism, it is deduced and testified by experiments that the materialremoval rate is direct proportion to the electric current density under steady state ofpolishing. Influences of voltage, temperature and concentration of the polishing solutionand the workpiece’s diving depth in polishing solution on the material removal rate areresearched basing on the experiments and analyses. The mathematic model of surfaceroughness with polishing time in electrolysis and plasma polishing is established. Theroughness of the specimen with different polishing time was measured. Nonlinear fittingof the experimental data and the mathematic model is carried out, by which themathematic model is improved. It is reasonable and feasible to use the improvedmathematic model to fit the experimental data. Two other group of experiments atdifferent temperature of the polishing solution were done to verify that the improved mathematic model is mainly in accordance with the actual polishing case.Orthogonal experiments consisting of four factors at four different levels wereperformed by using surface roughness of the specimens after some time of polishingand electric current density in the process of the polishing as experimental indexs basedon the polishing mechanism and the mathematic model of surface roughness withpolishing time. Primary and secondary order and regularity of the factors affecting theroughness and the electric current density are obtained by means of extreme differencemethod combined with variance analytic method. Optimal parameter combinationsfocusing on the polishing effects and considering fully the effects, cost, efficiency andstability are proposed. Conductometry is not available in detecting the polishingsolution concentration in electrolysis and plasma polishing because of the interferenceof the metallic particles produced in the polishing. To solve the problem, two methodsbased on experiment to detect concentration of ammonium sulfate in the polishingsolution are proposed. One method is to measure the current value and temperature ofthe polishing solution to determine whether ammonium sulfate needs to be added as theelectric current density drops significantly with the concentration less than2.5%. Theother method is to know correlations between the polishing quantity and theconsumption of ammonium sulfate in certain temperature of the polishing solution byexperiments and record the polishing quantity to work out the concentration ofammonium sulfate. The first method is simple to operate and suitable for generalindustrial production. The second method applies to the process requiring betterpolishing effect. The two methods are proved to be effective and feasible. Influence ofthe shape and spatial location on the polishing is studied for the workpiece withcomplex shape from two aspects: thickness of gas layer and electric field intensity. Thepolishing methods of specially shaped workpieces are investigated.According to the research results of the mechanism and process of electrolysis andplasma polishing, the equipment is designed and used to polish various materialworkpiece and supply a basis for the industrialized application.