Research On The Electrode Of Online Control Mechanism And Key Technology In Micro-EDM

Micro-EDM(Micro Electrical Discharge Machining)technology is considered to be one of the most promising methods for machining micro-deep holes and three-dimensional complex microstructures due to its wide range in materials machining and strong micro-scale manufacturing abilities.It is widely used in military defense,aerospace,information industry and biomedical equipment and other key parts machining.With the reduction of the size of the processing structure,electrode wear and control have become one of the key issues that restrict the engineering application of micro-EDM.This paper is acknowledged by National Natural Science Foundation of China under grant No.5 1005027 and General Program of Natural Science Foundation of Liaoning Province under grant No.201602030.With the goal of achieving micro-electrode control,the combination of experiment,simulation and theory was used to conduct research work from the following four aspects:Firstly,the research on the self-control technology of nanocomposite coating micro-electrode.Due to the frequent phenomenon of edge wear in homogeneous material electrodes,an electrode with heterogeneous ring structure was designed in this paper.The special structure of the electrode was used to reduce the edge wear rate in order to achieve uniform wear.On the basis of various manufacturing processes,the heterogeneous nanocomposite coating electrode was finally fabricated by ultrasonic composite electro-deposition process.The micro-EDM experiments showed that the nanocomposite coating had excellent heat resistance and weak electrical conductivity,which improved the electrical corrosion resistance of the electrode side face and improved the quality in the micro-EDM.Furthermore,by adjusting the process recipe,parameters and material composition,different compositions,different nano-particle materials and composite amounts were prepared to conduct micro-EDM experiments.The experiment summarized the rule between the electro-deposition process parameters and the erosion resistance of the prepared nanocomposite coating electrode.The nanocomposite coating electrode improves the quality in EDM,but the stability and reliability of the coating are not enough.It is necessary to change the way to further research.Secondly,the study of the change process in the discharge region under continuous pulse discharge conditions.The material erosion caused by the breakdown discharge is the cause of the breakdown discharge used for machining in the EDM process,and it is also the source of the uneven wear of the electrodes.In order to study the variation of discharge region,this paper improved the discharge channel breakdown model based on particle motion state,and proposed the probability that the electrical machining parameters,especially the peak current,discharge duration and pulse frequency,affected the discharge point in the discharge gap in different regions on the end face.Furthermore,the assumption of the shape of the electrode after the wear was affected,and then the shape change of the electrode under different conditions was obtained by means of single factor and orthogonal experiments.Experiments showed that the pulse-on and peak current determined the material erosion efficiency in the central and edge regions on the electrode end face within the range of the parameters studied.The experimental results were consistent with the above assumptions.On this basis,the region division theory of discharge erosion was established,and the theoretical basis of the online shape control technology of homogeneous electrodes was formed.In addition,the experimental study of the electrical machining parameters of the homogenized electrode.In order to establish the relationship between the electrical machining parameters and the shape of the end face of the electrode,this paper used image processing technology to extract the contour features of the electrode and workpiece after machining,and applied the nonlinear least squares method to fit the curve of the shape change of the end face in the micro-electrode under different electrical machining parameters.The data showed that under the condition of single factor experiments,with the increase of peak current,the edge wear of the micro-electrode increased rapidly and the concave shape disappeared;When only the pulse width was changed,the concave change in the end face of the electrode was remarkable and the edge wear was not substantially changed.Therefore,in the case of ignoring the processing efficiency,the process database between the electrical machining parameters and the shape of the electrode could be mastered by large-scale experimental data to meet the production needs.In addition,it is also found that in the experiment that the change of the lifting cycle of the electrode and the lifting speed had little effect on the concave shape of electrode end face,and the lifting action in the engineering was caused by the poor discharge state in the discharge gap.Therefore,it is necessary to study the role of debris in the shape change of electrodes.Finally,the mechanism of the influence of debris on electrode shape control was studied.In addition to the electrical machining parameters,it is believed that the distribution and concentration of the debris affected the shape of the electrodes.In order to accurately verify the relationship between the distribution and concentration of the debris and the shape changes of the electrodes,this paper designed an open state micro-EDM experimental method with indirect realization of the concentration of debris.The shape of the electrode and the composition of the material at the bottom of the workpiece under different discharge region conditions were analyzed,and the influence of debris on the shape of the electrode was excluded.On the one hand,the theory and experimental research of electrode shape control directly improve the quality in micro-EDM.On the other hand,it excluded the compensation difficulty caused by the shape change of the electrode and simplified the programming requirements,which had important theoretical value and reference significance for the engineering application of high-efficiency and high-quality of micro-EDM technology.