Research On Mechanism And Key Processes Of Electrolytic Jet Machining Of TB6 Titanium Alloy

Titanium alloy is widely applied to manufacture key aircraft components because of its excellent material properties.However,as a typical difficult-to-cut material,titanium alloy features high strength and toughness,making traditional machining techniques face severe challenges.Electrolytic jet machining(EJM)is a novel electrochemical machining(ECM)technique,which locally removes metal by anodic dissolution in electrolyte jet and manufactures arbitrary complicated patterns with cathodic nozzle translating.It combines merits of ECM and numerical control machining,becoming a potential precision machining technique for titanium alloy components.This dissertation takes TB6 titanium alloy as target material and research on the mechanism and key processes of EJM of TB6 titanium alloy.(1)Stationary EJM process based on traditional aqueous electrolytes was experimentally investigated.The results show that compared to NaNO₃ aqueous electrolyte,NaCl aqueous electrolyte is more suitable for EJM of TB6 titanium alloy.Larger machining voltage,smaller machining gap,and larger electrolyte concentration help improving materials removal rate and reducing surface roughness,but deteriorate machining localization.From the simulation of electrolyte reflection phenomenon,contact of reflected electrolyte and nozzle will cause discharge,which seriously affects machining stability.Dimples array pattern was successfully machined via optimization of process window.(2)Through the investigation of anodic dissolution behavior of TB6 titanium alloy in NaCl aqueous electrolyte,the transient evolution mechanism of anodic interface structure was obtained and a qualitative criterion to obtain uniform dissolution state was proposed.With the help of a 3D electric field model,the effect of parameters on machining performance in single-path translating EJM was investigated.The results show that larger machining voltage,smaller machining gap,and smaller nozzle translating speed help improving machining depth and reducing stray corrosion range,but cause larger overcut.Typical 2D linear patterns were successfully machined via optimization of process window.Experiments on superimposed-path translating EJM reveal that superimposing of nozzle path results in repeated formation of oxide layer,which leads to dramatically deteriorating of machining accuracy.(3)NaCl ethylene glycol(EG)-based electrolyte was proposed to be applied in EJM of TB6 titanium alloy and related process investigation was conducted.The results show that compared to NaCl aqueous electrolyte,this novel electrolyte has opposite current efficiency characteristics,can remarkably improve surface quality,effectively avoid formation of oxide layer,optimize the accuracy of superimposed-path translating EJM,and successfully manufacture precise 3D pattern.Scheme of high temperature electrolyte was proposed to overcome disadvantage of this novel electrolyte in incapability of using nozzle with small diameter,which can successfully realize machining of micro pattern.(4)A multi-physics microscale model considering anodic reaction kinetics equation and material microstructure was developed to simulate the supersaturated layer on anodic surface and reveal surface leveling mechanism of ECM.The results show that larger potential difference is beneficial to formation of the supersaturated layer,which helps leveling the micro protrusion on anodic surface,avoiding the local corrosion caused by the different electrochemical properties of material microstructure,and obtaining smooth machining surface.However,the effect of electrolyte flow rate on the surface leveling is relatively weak.Based on the simulated results of this microscale model and the macroscale electric field distribution of EJM,the formation mechanism of characteristic surface topography distribution in EJM of TB6 titanium alloy was revealed.