Ionization of the dielectric fluid allows the spark electricity to flowbetween the electrode and the workpiece. Electricity is the flow ofelectric charges. Figure 3-12 illustrates the flow of electrons from theelectrode with a negatively charged polarity to the workpiece that hasa positively charged polarity.During each spark, millions of electrons flow between the electrodeand workpiece at the approximate speed of light. The electrons traveleasily through the ionized column of dielectric fluid, but the surface ofthe workpiece is an obstacle. As electrons bombard the workpiece, releasingtheir energy in the form of heat, this vaporizes the workpiecesurface into a cloud. Since the workpiece has positive polarity, the vaporcloud is also positively charged. This positively charged vapor cloud isattracted to the negatively charged electrode. During the time that thevapor cloud is in transit toward the electrode, the spark electricity isturned OFF. This eliminates the vapor cloud’s electrical attraction tothe electrode. The dielectric fluid deionizes and the vapor cloud iscooled to form an EDM chip. Figures 3-13 through 3-16 illustrate thisprocess.The bombardment taking place within the ionized column of dielectricfluid is, in reality, more complex than described. During the spark,electrons are freed and attracted to the positive polarity. The atomsfrom which the electrons were removed become positive ions and areattracted to the negative polarity. Figure 3-17 illustrates the movementof electrons and positive ions within the spark-ionized columnwhen the electrode has negative polarity.When using negative electrode polarity, there are two actions takingplace. Negative electrons bombard the positive workpiece surfaceand positive ions bombard the negative electrode surface.
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