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MMM LECTURE NOTES FINAL.pdf

Depending on the grain size of these particles a

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Depending on the grain size of these particles, a constant interelectrode gap (0.025 mm or less) through which the electrolyte is flushed can be maintained. Fig., Surface ECG.
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Modern Manufacturing Methods The abrasives continuously remove the machining products from the working area. In the machining system shown in Fig. 6.3, the wheel is a rotating cathodic tool with abrasive particles (60 320 grit number) on its periphery. Electrolyte flow, usually NaNO3, is provided for ECD.The wheel rotates at a surface speed of 20 to 35 m/s, while current ratings are from 50 to 300 A. Removal rates by ECG are 4 times faster than by conventional grinding,and ECG always produces burr-free parts that are unstressed. The volumetric removal rate (VRR) is typically 1600 mm3/min. McGeough (1988) and Brown (1998) claimed that to obtain the maximum removal rate, the grinding area should be as large as possible to draw greater machining current, which affects the ECD phase. The volumetric removal rate (mm3/min) in ECG can be calculated using the following equation: Where e = equivalent weight, g I = machining current, A r = density of workpiece material, g/mm3 F = Faraday’s constant, C
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Modern Manufacturing Methods The speed of penetration of the grinding wheel into the workpiece, Vg (mm3/min), is given by Kalpakjian (1997) as follows: Where v = gap voltage, V gw = wheel-workpiece gap, mm Kp = coefficient of loss (1.5 3) k = electrolyte conductivity, Ω– 1mm 1 ECG is a hybrid machining process that combines MA and ECD. The machining rate, therefore, increases many times; surface layer properties are improved, while tool wear and energy consumption are reduced. While Faraday’s laws govern the ECD phase, the action of the abrasive grains depends on conditions existing in the gap, such as the electric field, transport of electrolyte, and hydrodynamic effects on boundary layers near the anode. The contribution of either of these two machining phases in the material removal process and in surface layer formation depends on the process parameters.
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Modern Manufacturing Methods The work of the abrasive grains performs the mechanical depolarization by abrading the possible insoluble films from the anodic workpiece surface. Such films are especially formed in case of alloys of many metals and cemented carbides. A specific purpose of the abrasive grains is, therefore, to depassivate mechanically the workpiece surface. Fig., ECD and MA in the machining gap during ECG.
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Modern Manufacturing Methods Applications The ECG process is particularly effective for 1. Machining parts made from difficult-to-cut materials, such as sintered carbides, creep-resisting (Inconel, Nimonic) alloys, titanium alloys, and metallic composites. 2. Applications similar to milling, grinding, cutting off, sawing, and tool and cutter sharpening.
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  • Fall '12
  • JeraldBrevick
  • EDM, conventional machining processes, Jet Machining

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