Research On The Corrosion Of Eletrodes And It's Theory Foundation In EDM

EDM, as a process different to conventional machining, is greatly used in manufacturing mould and automobile industry. None uniform theory about: EDM has been formed at present because of the complex EDM process. Some contents of former theory can't be used to explain all phenomenons in EDM, so we must continue to research and form perfect theory of EDM, which is important to accelerate the development of EDM.In order to research the influence to the deterioration of anode and cathode by the impaction of the moving electriferous particle in electric discharge channels and the insufficiency of the polarity effect theory, a series of systematic research is taken, which include monpulse EDM experiment, limited continuous pulse experiment and model analysis. At last, the main conclusion is proved in machining TC4 by EDMUsing same material electrodes whose shape are pin-board and club-club, monpulse EDM experiment is taken. The experiment can avoid the influence of the carbon-protection-film to weight change. So the real deterioration of anode and cathode can be gotten qualitatively. The result shows that the deterioration of anode is larger than that of the cathode even under electric discharge with large pulse width. The result is analyzed carefully from oscillation and bounce of the plasma channels on the electrodes' surface. One point that the result gained under single pulse discharge must not conform to the result gotten under continuous pulse in EDM is presented.Limited continuous pulse experiment is taken with changing the discharge energy and the discharge times. Limited continuous pulse experiment, which is between single pulse discharge and continuous pulse discharge, is not only convenient to find out the influence process of carbon-protection-film to electrodes but also easy to weigh the electrodes after discharge. With the dynamic changing of electrode's erosion along machining time taken into account, we analyze the movement law of electron and positive ion in plasma channels. We think the impaction of positive ion in plasma channels to cathode surface is very small no matter large or short the pulse width is. The point that the positive ion can impact the cathode surface with high speed and increase the cathode erosion under large width pulse discharge can't be confirmed.Precondition of how carbon-protection-film is formed and dynamic influence process of carbon-protection-film to electrode erosion are discussed. It is considered that the compensation of carbon-protection-film to anode erosion results in the cathode erosion bigger than that of the anode; under long time machining.A new point is presented that positive polarity machining should be taken for a period time no matter positive or negative polarity machining will be used. To take positive polarity machining for a period time not only can make discharge easy to be come into being but also can increase productively because of the anode erosion larger than that of cathode at the beginning of EDM when the asked work erosion is very small.After model analysis to EDM, we think it is photon but positive ion that sends energy by impacting cathode and influents the cathode erosion.A new polarity effect theory is presented based on our research and former polarity effect theory. Using the new theory, we succeed to explain the function of positive ion and electron in electric discharge plasma to electrode erosion in different medium such as gas, kerosene and water based medium. Uniform of EDM theory in different medium is realized. Our research improves the development of EDM theory.Experiment to prove the new theory is taken by using graphite electrode to machine TC4 in EDM. The result shows positive polarity machining should be taken no matter positive or negative polarity machining will be used because of it's large erosion speed. Scanning electron microscope and X-Ray diffraction are used to analyze the reason of no carbon-protection-film at the surface of TC4 after EDM.