Research On Electropolishing Of Micro Grooves/Micro Holes

As an important evaluation criterion for processing quality,the surface quality of microstructures has an important influence on their working performance and service life.In order to eliminate surface defects such as the thermal impact layer generated in the high-energy beam manufacturing process and the burr generated in the machining process,polishing techniques are applied to improve the surface quality.Electropolishing is a non-contact process with the advantages of no limitation to strength and hardness of materials,freedom from stress,an absence of workpiece deformation,ability to obtain smooth surface with low surface roughness and so on.As the material is removed in the form of ion in electropolishing process,the polishing precision can theoretically reach the ion level,which enables electropolishing to polish structures and component at a micro scale.Micro grooves and micro holes are two widely used microstructures.In this paper,research work on electropolishing of micro grooves and micro holes have been carried out as listed below:(1)A wire electropolishing method has been proposed for polishing micro groove structures.The polarization curves of the cobalt-based alloy 3J21 in phosphoric acid solutions were measured.Based on the polarization curves,the passive–active–repassive–transpassive dissolution process of 3J21 alloy in phosphoric acid solutions was analyzed.The formula of material removal in the electropolishing process was derived.The formula shows that increases in the polishing gap and the feed rate will decrease the material removal and increases in the wire electrode diameter and the voltage will increase the material removal.(2)An electric field model for electropolishing of micro groove structures was established.The simulation results indicate that the current density in wire electropolishing increases first and then decreases due to the movement of the cathode.The variation of current density contributes to the formation of the passive film after polishing.Under the same conditions,the material removal rate and the material removal amount in wire electropolishing are smaller than that in electropolishing using a square electrode.The deflection of the square electrode around the center axis results in a poor repeatability of polishing process and thus the square electrode requires a higher precision of installation.There is an unpolished area at the corner of the micro groove in the wire electropolishing process.Using a wire electrode of smaller diameter can reduce the unpolished area.(3)A wire electropolishing experimental system was developed.Polishing experiments of micro grooves were carried out on this system.The influences of the wire electrode diameter,feed rate,polishing gap,applied voltage,pulse period,duty cycle and electrode shape on polishing effect were investigated.The material removal formula and the electric field simulation results are verified by the experiments.The experimental results also indicate that the surface roughness of polished surface is neither positively nor negatively correlated to the polishing parameters,namely,the voltage,pulse period,duty ratio,feed rate and polishing gap.These parameters should be controlled in a suitable range to obtain a best polishing effect.The micro groove with initial surface roughness of Ra 0.304?m was polished under optimal condition and a bright surface with surface roughness of Ra 0.036?m was obtained after polishing.(4)An experimental system was developed for polishing micro holes.The polishing conditions were explored preliminarily.The influences of the voltage,polishing time,frequency,duty cycle and polishing gap on defects removal effect were studied.The experiments show that the defects can be effectively removed under optimized parameters.