Research On Electrochemical Mechanical Polishing Technology Of Micro-hole By Using Electric Discharge Machining

Electromechanical system and structure miniaturization have become a mainstream trend in the development of machinery industry. Micro-hole part, as one of the most basic parts in micro-electromechanical system, is widely used in aerospace engines, artificial blood vessel scaffold, fuel nozzle, etc. Micro-hole parts have small size, can carry low load and their surface quality often determine their performance, so the researches on the surface quality is of great importance. Micro electric discharge machining is one of the commonly-used methods in current micro-hole machining, but the micro-holes processed in this way have a lot of defects such as heavy recast layer, cracks, burr as well as surface roughness and bigger surface taper. In order to solve the problem, the thesis puts forward the method of electrochemical mechanical composite polishing processing of micro-hole by using electric discharge machining so as to greatly improve the surface quality of parts on the basis of the high efficiency.Based on the analysis of the process conditions of micro-hole combination requires, the combination machining platform integrating block electrode electrosparking grinding, electric discharge machining and electrochemical mechanical composite polishing processing is established. Besides, the fundamental experimental study of the combined technology of electric discharge machining and electrochemical mechanical composite polishing is conducted on the processing platform; Φ120μm micro electrode is prepared; the combined electric discharge machining parameters such as appropriate voltage, current, capacitance and pulse width are selected; the micro-hole surface quality of electric discharge machining and combined processing is compared; the proper processing time(around 90s) of electrochemical mechanical composite polishing is selected.The simulation is conducted on the gap flow field of micro-hole processed by electrochemical mechanical composite polishing method; the velocity distribution, particle concentration distribution and motion curve of gap flow field under the different conductions of electrode feed speed and particle mass concentration are analyzed. On the basis, the influence of processing voltage, pulse width, electrode feed speed and particle mass concentration on the surface quality and machining efficiency of microhole by electrochemical mechanical composite polishing processing is studied; the simulation results are verified. The reasonable processing parameter ranges of microholes with electrochemical mechanical composite polishing processing method are obtained, namely, processing voltage: 10~20v; pulse width: 0.5~1.5μs; electrode feed speed: 0.4~1.2 mm/s; particle mass concentration: 3~9wt%.Based on the above work, the process experiment is planned with the method of center combination experiment. Response surface methodology is used to establish the mathematical model of processing voltage, pulse width, and electrode feed speed, particle mass concentration as well as surface roughness of micro- holes. Based on the model, the particle swarm optimization algorithm is applied to optimize the processing parameters; the optimum technology parameter combination and the theoretical value of minimum surface roughness are obtained. The optimization results are validated through the experiments; the error is less than 10%. Finally, the micro-hole with 200μm of aperture, 1:3 of ratio of depth to diameter and 36 nm of surface roughness is successfully processed.