Electrochemical Machining Of Small Holes Using Hollow Circulating Electrodes And Its Application In Residual Stress Measurement

Residual stress refers to the stress that still exists in the material after the external action is eliminated,which affects the mechanical properties of components such as fatigue strength,stress corrosion resistance and creep resistance,thereby affecting its performance and service life.Therefore,the research on accurate and reliable residual stress measurement methods is of great significance in engineering practice.The small hole method is the most widely used method for measuring the residual stress near the surface of mechanical parts in the engineering practice.At present,when the small hole method is used for measuring residual stress,usually mechanical methods such as drilling and milling are used to process the small holes.The mechanical machining of small holes belongs to contact processing.Additional stress and plastic deformation are easily introduced to the specimen in the process of traditional mechanical machining of small holes,which cannot accurately reflect the residual stress distribution on the surface of the specimen.Electrochemical machining(ECM)is a non-contact special processing method that uses the principle of electrochemical anodic dissolution of metal in the electrolyte to form a cathode with a specific shape.Plastic deformation and additional stress will not be introduced during the processing.The electrochemical machining of small holes can effectively eliminate the influence of mechanical machining small holes on the results of residual stress measurement.In this paper,the pure iron material(DT4E)is used as the research object to carry out the related research on the measurement of residual stress by electrochemical machining of small holes.3D printing technology was used to design and manufacture hollow circulating auxiliary electrodes,and the experimental device for electrochemical machining of small holes by hydrodynamic electrolyte was built.Aiming to optimize the internal flow channel structure of the hollow circulating electrodes,Fluent software was used for flow field simulation,and the flow rate of the electrolyte and the uniformity of the flow field on the ECM surface were used as the evaluation standard.And the experiment of electrochemical machining of small holes with different wall angle ? was carried out.The best separator wall angle ? value of hollow circulation electrode was selected by observing the shape of small holes.The electrochemical characteristics of pure iron materials are studied,and the appropriate electrolyte composition and concentration was optimized through comparison experiments of electrochemical machining of small holes.At the same time,when the small hole method is used to measure residual stress,the amount of anode metal removal needs to be strictly controlled.Based on Faraday's first law,the constant current machining mode was adopted,and the amount of anode metal removal can be controlled by controlling the electrochemical machining time.The relationship between anode metal removal and ECM time was corrected through ion measurement and experimental calibration.The holes by electrochemical machining are circular arc holes.In order to analyze the influence of the circular arc hole on the stress release of the specimen,Abaqus software combined with the life and death element method was used to simulate the stress field of the specimen with circular arc hole and right-angle hole respectively.Finally,the pure iron specimens were pretreated with stress relief annealing and prefabricated tensile stress.The device for electrochemical machining of small holes and the device for strain measuring were combined to build a platform for measuring residual stress by the method of strain-electrochemical machining of small holes.The comparison experiment for residual stress measurement on specimen was carried out by using the method of electrochemical machining of small holes and the method of mechanical machining of small holes respectively.The error of residual stress measurement by electrochemical machining of small holes was relatively small.Therefore,the measurement accuracy of residual stress can be significantly improved by using electrochemical machining of small holes.