Theoretical Analysis Of Electrical Discharge Channel And Research Of GAP Distance Testing

With the continuous deepening of EDM processing technology research, the mechanism of EDM is lagging behind to some extent restricted its further development, because of the complex and transitory of discharge process. Every electric discharge is a complex process of interaction between many factors, including electromagnetics, fluid mechanics, thermodynamics, the role of electrochemistry and colloid chemistry, and so on. The motion characteristics and electromagnetic characteristics of charged particles in the plasma channel during the discharges cannot be understood well because of the complexity of discharge.The basic equation of plasma channel dynamics was introduced based on the basic theory of EDM and the theory of DC discharge plasma. The breakdown process of plasma channel and the particle movement in the plasma channel during electric discharging was analyzed in the further. The expressions of the breakdown voltage and cathode voltage drop were obtained according to the empirical formula of plasma channel radius. It was found that the breakdown voltage and the cathode voltage drop is mainly decided by the dielectric, electrode material and the pressure during the normal glow discharge, while the current density has little effect on them. The cathode voltage drop remained stable during the electric discharging.The ions density and speed in the cathode sheath can be calculated with the value of cathode voltage drop, and then, the energy of the ions which impact the cathode surface can be got. It was found that the ions bombardment energy is mainly decided by the peak current, pulse time, the cathode voltage drop and cathode thickness. A new method was designed in this paper. The critical gap distance tests and the single pulse discharge experiments by the functions and capabilities of the EDM machine tool itself without any improvement of the EDM machine tool or any other control circuit or equipments can be accomplished with this method with high accuracy. The influence of the gap distance on the discharge crater was found with this method. It was found that the peak current does not affect the critical gap distance for a discharge of fixed electrode and workpiece, it only affects the sizes of discharge craters. It was also found that the crater dimensions on the surface of workpiece and electrode increase with the decrease of the gap distance, and the crater dimensions increase faster while the gap distance is smaller, when other processing conditions don't change. The experiments qualitatively verified the analysis of breakdown voltage and ions bombardment energy.A method of testing the relative gap distance was designed, and the relative gap distances of steel and cemented carbide which used copper as the reference material were measured with this method.