Research On Technology And Mechanism Of Ultrasonic Vibration Assisted Electrolytic Grinding For Machining GH625 Nickel Base Superalloy

GH625 nickel-based superalloy has the advantages of high strength and high hardness,and is widely used in energy industry and other fields.With the improvement of material properties,the difficulty of material processing also increases.Using traditional processing methods to process nickel-based superalloys has problems such as high grinding heat,fast tool wear,and hardened surface,which reduces the surface quality and dimensional accuracy of superalloys.Ultrasonic Vibration Assisted Electrolytic Grinding(UAECG)is an effective machining method that combines ultrasonic vibration machining,electrolytic machining,and mechanical grinding machining.The high-efficiency and precise processing of materials can be achieved by using the corresponding combination of electrochemical dissolution,mechanical grinding,ultrasonic vibration cavitation effect and liquid phase mass transfer effect.In this paper,ultrasonic vibration-assisted electrolytic grinding is used to process small holes in GH625 nickel-based superalloy,and its processing technology and mechanism is studied as well,as follows:1.The processing principle of ultrasonic-vibration assisted electrolytic grinding technology are expounded,and the experimental processing platform of ultrasonic vibrationassisted electrolytic grinding is set up,including motorized spindle control system,highfrequency pulse power supply system,processing machine tool and electrolyte circulation system,and to optimize the fixture.2.An electrolytic experimental platform based on three-electrode system is set up and used to test the polarization curves of GH625 nickel-based superalloy.The polarization curves of the superalloy materials in different composition and concentration electrolyte at different temperatures are obtained.The polarization behavior and passivation effect of the superalloy surface under different experimental conditions are analyzed,NaNO3 electrolyte with temperature of 20℃ and concentration of 10wt.%is finally determined for experimental study.Based on the current efficiency of GH625,the relation between material removal rate and current density is analyzed,and the current efficiency curve is drawn,the microstructure,morphology and surface quality corresponding to different current density are obtained,and the electrolytic etching process law is revealed.3.The mathematical model of ultrasonic vibration-assisted electrolytic grinding(UAECG)is established,and the machining law of UAECG is analyzed with electrolytic machining theory.The physical models of pre-machined small holes and reaming holes are established and the flow field distribution in the gap is simulated.During the reaming process,different rotating speeds are applied to the cathode grinding head through the sliding grid technique,the velocity distribution and pressure distribution of the field in the gap are analyzed.The simulation results show that with the increase of cathode rotating speed,the velocity and pressure of the field in the gap are increased,the products are discharged out of the machining zone and the new electrolyte is added to the machining gap in time,optimized the processing environment.4.The experiments of ultrasonic vibration assisted tube electrode pre-machining holes and ultrasonic vibration-assisted electrolytic grinding hole reaming of GH625 nickel-base superalloy are carried out on the experimental platform.The effects of pulse voltage,feed speed,cathode speed,electrolyte concentration,duty cycle and amplitude ratio on the machining quality and accuracy of the small holes are studied respectively,high efficient precision machining of GH625 nickel-base superalloy is obtained with the best combination of machining parameters.