�Confined Etching�Electrolysis� Composite Electrochemical Machining On TC11

Titanium alloy has been applied in many fields,especially in aviation and aerospace industry,chemical industry,automobile industry and other fields because of its high specific strength,good corrosion resistance and other advantages.Due to its poor machinability,many researchs were focused on how to solve the problems of titanium machining.Electrochemical machining becomes an ideal choice to solve above problems.Electrochemical Machining(ECM)has high processing efficiency,but it has a disadvantage of poor machining precision.Confined Etchant Layer Technique(CELT)is a new micro or nano machining technique.It can achieve high machining precision for three-dimensional microstructures.In order to achieve good machining precision and high machining velocity,present paper proposed to integrate the Electrochemical Machining(ECM)and Confined Etchant Layer Technique(CELT)to form a precision composite machining technology.That is,"Electrolysis-Confined etching" electrochemical composite machining technology.It is expected to have both high machining velocity and high machining precision.In this paper the principle and development of several current composite electrolytic machining technology and electrochemical micromachining technology were reviewed and analyzed.The characteristics of ECM and CELT were discussed emphasisly.The possibility and necessity of integrating two kinds of processing technology were evaluated.According to the principle of the ECM and CELT,the composite method of ECM and CELT was designed.When the mold electrode acts as anode and the workpiece acts as cathode,the confined etching process was carried out;when the mold electrode acts as cathode and the workpiece acts as anode,the electrolytic machining occurred.The composite mode in this research was conducted by alternating between the ECM and CELT,which was achieved by a bipolar power supply.Through a series of experiments,such as weight loss,Tafel polarization curve and Cyclic voltammetry curve,an appropriate electrolyte system for confined etching of TC11 was determined.The redox effect of F-on NaNO2 and the trapping effect of OH-on H+ were discussed and analysised.The confined etchant processing of titanium alloy was carried out,and the reasonableness of the etching system was verified.Under the etching process,the depth of etching hole was 12.659?m and the machiningvelocity was 22.68?m/h.Based on a set of single factor tests and orthogonal tests for the composite electrolyte system of machining TC11,a composite electrolyte system was ultimately determined which was suitable for both ECM and CELT.The composite electrolyte system was : 0.3mol/L NaCl+0.3mol/L NaNO3+0.6 mol/L NaNO2+0.3mol/L NaF+0.4 mol/L NaOH+0.4g/L malic+0.2g/L cetyl trimethyl ammonium bromide.Under the composite process,the machining precision was 0.46?m,the depth of etching pits was 45.396?m,and the processing velocity was 81.71?m/h.In compared with the confined etching process,"Electrolysis-Confined etching" composite machining technology had greatly improved the machining velocity.The influence of the temperature of the electrolyte,the machining voltage and the working gap on the machining precision was studied by the Response Surface Methodology,the interaction between the factors was analyzed and the optimal combination of parameters was determined.The optimum process parameters were:voltage:1.7v,feed rate:0.17?m/100 s,temperature:22?C.The machining precision was0.46?m of the etching pits,the depth of etching hole was 55.475?m,and the machining velocity was 99.86?m/h.Thus the experiment showed the good characteristics of both high precision and high velocity of "Electrolysis-Confined etching" composite machining technology.At the end of this paper,three-dimensional microstructure of titanium alloy was fabricated by CELT,and the microstructure was formed on the titanium alloy.The machining precision on the height was 0.383?m,the relative error was 3.59%;the machining precision on the diameter was 0.912?m,the relative error was 0.88%.The machining precision was sub-micron,and the advantages of high resolution of the CELT were verified.In this paper,the composite machining technology of "Electrolysis-Confined etching" was studied,and it is believed that the "Electrolysis-Confined etching" composite machining technology have great propect for application in the field of microstructure machining in the future.