Principles And Key Process Investigation On Electrochemical Micro-machining Of Titanium Alloy Based On Water-free Ethylene Glycol Electrolyte

Titanium alloy is widely applied in weapon manufacturing,aerospace and medical instrumentation due to its properties of low density,high strength and excellent corrosion resistance.Usually,the components applied in these industries contain many accurate micro features,such as the smooth micro-holes and micro-pins in artificial implants,the micro-channels in fuel cell,and the heat dissipation holes in turbine blades.Considering the low stiffness of micro-tools and the high processing difficulty of titanium alloy(due to its high strength and hardness),the micro features are hardly manufactured in mechanical methods.Electrochemical micromachining(EMM)removes useless material at the effect of electrochemical corrosion.EMM has some inherent advantages in shaping of hard metal materials,and thereby becomes a promising micromachining method for titanium alloy.However,two key technical problems should be solved to machine titanium alloy micro-structures.One problem is the manufacturing of high-quality micro electrodes used in EMM process.The other problem is that poor machining accuracy is obtained due to titanium's self-passivation properties.To solve these key technical problems,the following works were done in this paper.According to the flowing state of diffusion layer during electrode reactions,a novel machining method for micro-electrodes using quasi-solid electrolyte(agarose hydrogel)has been proposed.In water solutions,liquid diffusion layer flows and decreases the machining accuracy of micro electrodes.Whereas,quasi solid electrolyte enables uniform distribution of diffusion layer,and thereby fabricates micro electrodes with high aspect ratio and small taper angle.Effects of main parameters,including vertical distance,duty factor,and pulse peak voltage,on machining accuracy were investigated and the processing parameters were optimized via single variable experiments.To deal with titanium's self-passivation properties,a new method based on waterfree electrolyte,ethylene glycol-based electrolyte,was developed to manufacture micro-structures on titanium alloy.To study the electrochemical corrosion properties,the polarization curves,electrochemical corrosion process and final corrosion surface of titanium were compared and analyzed in both water-based and ethylene glycol-based electrolytes.In water-based solutions,oxide film forms constantly on titanium surface during anodizing,and decreases the machining accuracy.In ethylene glycol-based electrolyte,new oxide film stops forming after breakdown of air-formed oxide film,which helps forming a polished surface.Using a self-build electrochemical machining station with high moving accuracy,EMM experiments machining micro-holes were conducted in NaCl-containing ethylene glycol electrolyte.Effects of main parameters on the machining performance were experimentally investigated,including peak voltage,pulse width,and feeding rate.According to the experiments,the peak voltage of 40 V,pulse width of 25 ?s,and feeding rate of 1 ?m/s were selected as the optimum parameters.Using the optimum parameters,a deep-micro-hole with 300 ?m depth and 148 ?m average diameter was successfully machined on titanium alloy.In NaCl-containing ethylene glycol electrolyte,EMM experiments of micro-grooves were conducted by moving workpiece in the X-Y plane.The influenced factors of machining accuracy were analyzed.Effects of main parameters on EMM machining performance were experimentally investigated,including moving rate,initial interelectrode gap,and pulse potential.And moving rate of 3 ?m/s,initial inter-electrode gap of 10 ?m,peak potential of 30 V were selected as the optimum parameters.Using the parameters,a “TJU” shaped micro-structure with high shape accuracy and good surface quality was finally machined.