Study Of Electrode Jump Motion And EDM Performence

According to the nature of Die-sinking Electrical DischargeMachining(EDM), effective evacuation of debris from the discharge gap isof significant importance. Concentration of the debris will affect themachining performance by degrading the dielectric strength of the workingfluid, or even lead to localized discharging, arcing or short circuiting,thereby resulting in lower Material Removal Rate and higher Tool WearRatio. It may also deteriorate the integrity of finished surface and evendiscontinue the machining process while the debris concentrated severely.Therefore, tool electrode jump motion is usually used to improve the EDMperformance, especially in cases of narrow-slot or deep-hole machining.In order to understand the mechanism of how the electrode jumpmotion improves EDM performance, a series of experimental investigationinto narrow-slot EDM followed by analysis were conducted, and its effectson MRR, TWR and effective discharge frequency were taken into account.Electrode jump motion can decrease the debris concentration in themachining gap, and assure stable machining. To study the consequent fluidflow and debris concentration, the high speed and normal speed jumpmotions were simulated by using Computational Fluid Dynamics softwareANSYS FLUENT. Based on two-phase flow theory, this study investigatedthe fluid flow, the debris movement as well as the debris concentration inthe machining gap.Finally,2mm wide and100mm deep narrow slot EDM was conductedwith typical electrode materials, copper and graphite. As a result,machining efficiencies of normal speed and high speed jump motion werecompared by means of achievable machining depth, machining speed andelectrode wear. The experimental and simulated results show that the electrode jumpmotion can significantly lower the debris concentration in the bottom gap,so it facilitates the efficient discharging. The high speed motion is differentfrom the normal one in expelling debris, and, a large proportion of debrisare evacuated from the machining gap including the bottom and the side aswell. Therefore, the debris concentration becomes lower and the debrisdistribution tends to evener, thereby the machining efficiency and stabilityare improved.Experiments and simulations in this thesis may provide importantreferences for better understanding of the effects of jump motion on theEDM machining performance.