Study On Ultrasonic Assisted Electrochemical Grinding Of Small-holes With High Efficiency

Small-hole structure is widely used in many engineering fields such as 3D printer nozzles,engine nozzles,film cooling holes of the blade,profiled holes of the spinneret plate and so on.With the rapid development of Micro-Electro-Mechanical systems(MEMS),the size of the parts and components becomes increasingly miniaturized.The surface quality of the hole directly determines the quality and performance of the small-hole structure.Therefore,the machining of small holes with high precision has been a research hotspot worldwide.To further improve the machining accuracy and surface processing quality of small holes,this thesis presents an ultrasonic assisted electrochemical grinding technique in which ultrasonic vibration technology is employed with electrochemical grinding for expanding small holes with high precision and efficiency.In ultrasonic assisted electrochemical grinding,the machining environment is optimized benefited from cavitation and mass transfer enhancement of the ultrasonic vibration.In this thesis,a set of numerical simulation and experiments of ultrasonic assisted electrochemical grinding are carried out.The main research contents are as follows:(1)First,the experimental set-up of ultrasonic assisted electrochemical grinding is constructed,including electrochemical machine,ultrasonic machining spindle,ultra short pulse power supply,data acquisition system of current and so on.,diamond abrasive ball-end electrode was developed to make the side wall of small hole treated by ultrasonic-assisted electrochemical grinding enlargement basically taper-free.And the diamond abrasive ball-end electrode is prepared.By using the electrode,small holes without taper are fabricated.(2)The polarization curves of superalloy GH3030 in electrolyte with different composition and concentration has been measured.And the electrochemical behavior of superalloy GH3030 in different electrolyte is obtained.Based on the polarization curve measured,the effects of passivation under different electrolyte conditions are analysed.(3)The mathematical model of ultrasonic assisted electrochemical grinding is established,and the mechanism of ultrasonic assisted electrochemical grinding is studied.The current density of the gap electric field and surface profile change of small hole are simulated.The results show that the taper of small hole can be effectively reduced by using ball-end electrode.The influence of ultrasonic vibration on electrolyte in gap flow field is studied by simulation.The pressure distribution and velocity vector of the flow field in the machining are obtained which show that the ultrasonic vibration of the tool electrode can promote the electrolyte circulation and take away the electrolysis products in time(4)A set of experiments of ultrasonic-assisted electrochemical grinding on 0Cr18Ni9 stainless steel and superalloy GH3030 for expanding small holes are carried out.The influence of several parameters such as power supply parameters,feed rate,rotating speed,grinding head grain size and ultrasonic vibration amplitude on the machining accuracy and surface quality are studied.And reasonable matching between electrochemical reaction and mechanical grinding is realized in the machining process.Finally,small holes with high machining precision and surface quality are obtained by using the optimized machining parameters.