Abstract
In electrical discharge machining (EDM), gap control is the key to stable processing; the discharge gap plays a significant role in EDM. To determine the influence of the discharge gap on material removal and melt pool movement, which are two fundamental issues in EDM, high-speed photography and molecular dynamics (MD) simulations were used to study the discharge process. Research results demonstrate that the discharge gap has a significant influence on material removal during the discharge process. A smaller gap width produces more and larger removed materials. The influence mechanism of the gap width on material removal is explained as follows. A smaller gap width produces discharge plasma with a smaller diameter and greater heat flux. Discharge with a greater heat flux generates more material removed during the discharge process. In addition, a smaller gap width and greater heat flux produce a stronger interaction of metal vapor jets, generating a stronger shear force acting on the melt pool. The discharge gap also influences the movement of the melt pool and the final topography of the discharge crater through external pressure acting on the melt pool. Smaller gap width produces greater external pressure acting on the melt pool, generating a bowl-shaped melt pool and a discharge crater with a depression in the center and a bulge around the edge. A larger gap width produces less external pressure acting on the melt pool, generating a flat melt pool and a discharge crater with swelling in the center and a depression around the edge.
Highlights
As non-conventional processing technique, electrical discharge machining (EDM) uses thermal energy to machine any electrically conductive material into complex precision components regardless of its hardness, rigidity, toughness, and strength
In electrical discharge machining (EDM), gap control is the key to stable processing; the discharge gap plays a significant role in EDM
The discharge gap influences the movement of the melt pool and the final topography of the discharge crater through external pressure acting on the melt pool
Summary
As non-conventional processing technique, EDM uses thermal energy to machine any electrically conductive material into complex precision components regardless of its hardness, rigidity, toughness, and strength. In EDM, the workpiece materials are erased through melting and evaporation by the plasmas in the continuous pulse discharges.[3] To ignite the discharge, the width of the discharge gap must be small (several micrometers to tens of micrometers). In which the tool is fed in the constant velocity, the feeding speed of the tool electrode is not constant in EDM, and the discharge gap must be controlled at a proper width by the servo feed control system.[3] If the working gap is too large, the discharge cannot be ignited; if the working gap is too small, short circuits or abnormal discharges frequently occur. As EDM has a strict requirement for the gap condition, and the working gap has a substantial influence on the machining process, the discharge gap has become a research focus
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