"Confined Etching-Electrolysis" Composite Electrochemical Machining On Titanium Alloy

Due to the conventional electrolytic machining can’t work in a fixed location stably,machining gap is changeable, and prone to take place stray corrosion, etc., so theworkpiece always has low machining precision and inferior surface quality. In view ofthis, based on the principles of the confined etchant layer technique (CELT), the presentpaper proposed a new type of electrochemical machining method, that is,“Confinedetching–electrolysis” composite (hybrid) electrochemical machining technology whichcombines CELT with traditional electrochemical machining method. The new methodmakes use of the advantages of CELT of distance sensitivity and machining complexthree-dimensional structure with high precision, etc. It makes up for the disadvantagesof traditional electrochemical machining technology. The composite machiningtechnology has extensive application prospect in the field of special processing in thefuture.The paper summarized the progress and developing trend of the currentelectrochemical machining over the world, and expounded the basic principles, researchstatus, and application of the confined etchant layer technique. Its advantages anddisadvantages were analyzed. The composition of the electrolytes for CELT had beendetermined preliminarily for titanium alloy by thermodynamic parameters, Tafelpolarization curve, cyclic voltammetric curves and electrochemical impedance spectrum,etc.The “Confined etching–electrolysis” composite (hybrid) electrochemicalmachining technology was conducted through the alternating of electrolytic machiningand CELT machining. When the mold was used as anode, the workpiece was used ascathode (or let it on open circuit state), the confined etchant layer technique machiningwas running; when the mold is used as cathode, the workpiece was used as anode, theelectrolytic machining was running. The transformation of the electrode polarity can beimplemented by asymmetric bipolar square wave pulse power or double-poledouble-throw switch.A series of monofactor and orthogonal experiments were done for the compositeelectrolyte system and the processing conditions of the composite machining. Acomposite electrolyte system was obtained for titanium alloy, which was suitable notonly for confined etchant layer technique but also for electrolytic machining technique. Under the conditions that pulse power processing was adopted (optimal frequency300Hz, duty cycle1:12), the optimal processing voltage was6V, the running speed of cyclicpump is200r/min (it controlled the rate of flow of electrolyte), processing time wasabout60min, a half sphere with high machining precision and fine surface quality wasobtained.Finally, a preliminary research of the micro processing for the titanium alloy wascarried out. The effect of scavenger on processing was tested. The effects of someparameters on confined etching were analyzed. It laid a foundation for the titanium alloymicro processing by CELT in the future.