Experimental Research On Electrochemical Micromachining Of Micro-Slits/Grooves Into Cobalt-Based Alloy In Phosphoric Acid

Micro slits and grooves used in microelectromechanical systems(MEMS)are small,precise and usually made of hard-to-machine material,whose surface roughness significantly affects their performance and service life.Wire electrochemical micromachining(WECMM)which exhibits the advantages such as no tool wear,no contact between the tool and the workpiece,no workpiece deformation,no heat-affected zone and removing material in ionic units theoretically has been used to machine them.However,sometimes,it takes extra time to polish the microgrooves produced by WECMM when they couldn’t meet the requirement of some special products in terms of surface quality,resulting in low efficiency.In this study,a new method is proposed to produce high quality surface efficiently that simultaneously implements electrochemical cutting and polishing in phosphoric acid(H3PO4).Investigations were carried on as followings(1)The principle of WECMM in phosphoric acid has been studied.To investigate the dissolution behavior of 3J21 alloy in H3PO4 solution,Polarization curves were measured.The principle of polishing was explained.Through the simulation of the electric field in the processing area,the current density distribution of the side wall of the slit was analyzed,and the principle of simultaneous cutting and polishing was explained.(2)Experimental setup of micro electrochemical machining was improved,which was used for the experiments on machining of micro slits and grooves.Average value and standard deviation of the width of the slits are important factors of measuring machining precision.The effects of electric parameters and feed rate on the quality of machined slits were studied experimentally by the investigation of average value and standard deviation of the width of the slits.In optimal condition,a microgroove with bright surface was fabricated.Simultaneously cutting and polishing of metal microstructures was proved feasible both theoretically and experimentally.However,affected by the low efficiency of mass transport,surface of the microgrooves fabricated in aqueous H3PO4 was curved.Mathematical expression of the curvature of the microgrooves was founded and the effects of factors such as the concentration of the electrolyte and pulse condition on the curvature of the surface were investigated.(3)To reduce the curvature of microgrooves,ethanol,which has a lower density than water,was added to the electrolyte to improve mass transport innovatively.The polarization curves of H3PO4 C2H5OH solution showed that ethanol won’t essentially change the characteristics of phosphoric acid.The addition of ethanol made the transport of electrolytic products more smoothly,conductivity of the electrolyte in the machining gap was more even and steady and curvature of the microgrooves were reduce even eliminated.However,Addition of ethanol would reduce the conductivity of the electrolyte There shouldn’t be too much ethanol in the electrolyte to ensure machining efficiency.Effects of machining parameters(including pulse condition and feed rate)on surface roughness and radius of the microgrooves were studied.In optimal condition,a microgroove with no obvious defect and surface roughness Sa=0.039 μm,Ra=0.033 μm was obtained.