Molecular Dynamics Simulation Of Micro Edm Machining Process Using Minimal Discharge Energy

Since 1943 the Soviet scholars Lazarenko invented EDM methods,the EDM technology has achieved considerable development,its scope of application has also made a great extension.However,The EDM mechanism has yet to be explained clearly,which limits the further development of EDM technology. EDM occur in a very small space and time scale,the material ablation process is difficulty to be observed and analysised by experimental or theoretical methods.With the development and impact of the high-speeding milling technology,how to improve the efficiency and quality of EDM becomes an urgent problem for the EDM researchers .Therefore, The EDM material ablation process,the molten material ablation mechanisms,the residual stress and the formation of the bulge of discharge crater and the evolution of the dislocation defects were researched in this paper.In this paper,the micro-EDM discharge removal process,the formation and shape of electrode molten zone was analyzed based on discharge channel expanding model. It can be concluded that the discharge channel expanding model is more realistic compared with the simulation results under the discharge channel constant model.The article also analyzed the electrode temperature and the ablated atoms variation during the discharge process and explained the secondary ablation phenomenon of electrode materials and the existence of the"latent heat"phenomenon.The velocity vector,the acceleration vector and the spatial distribution characteristics of the gap atoms were studied at the same time.The residual stress is one of the main characteristics of the surface machined by EDM, as the existence and presence of the residual stress affects the machined surface quality and performace, the study of the formation mechanism and influencing factor of the residual stress are of great significance. In this paper, the formation mechanism of the surface residual stress, the distribution and the influencing factor was simulated. Through the analysis of the internal pressure of the melting area during the crater forming process, it can be found that a large pressure gradient was formed in the melting region with the discharge carried on. From the melting area pressure changing curve it can be known that before the end of discharge in micro EDM the pressure of melting area has not increased consistently but fluctuated, while right after the end of the discharge the discharge channel suddenly vanished and the pressure rapidly declined. It can be concluded that there existed the materials ablated during the discharge duration and on the other hand that the"overheating"after the discharge is the main mechanism of EDM material ablation.It was also found that the shear stress field caused the plastic flow of the electrode materials, which was the important reason for the formation of the discharge crater and bulge. From the distribution of the residual stress, it was found that the residual stress in the re-solidified layer is tensile while it is compressive in the heat-affected layer, indicating that cracks are easy to be generated in the re-solidified layer.The study of the defects generation and evolution mechanism was conducted in this paper. The phase transition of EDM material ablation process was identified by the radial distribution function analysis of the melting atoms.It can be concluded that it was impossible to obtain the non-crystalline structure with good performance in vacuum or gas discharge conditions.While the defect generation mechanism,the changing process of defects and the influencing factor was researched by central symmetry parameter methods and clear the defects influence on the discharge process and the workpiece surface quality.