MMM LECTURE NOTES FINAL.pdf

With this method flushing occurs only during the

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some machines. With this method, flushing occurs only during the nonmachining time as the electrode is retracted slightly to enlarge the gap. Increased electrode life has been reported with this system. Innovative techniques such as ultrasonic vibrations coupled with mechanical pulse EDM, jet flushing with sweeping nozzles, and electrode pulsing are investigated by Masuzawa (1990). 1. Flushing through the tool is more preferred than side flushing. 2. Many small flushing holes are better than a few large ones. 3. Steady dielectric flow on the entire workpiece-electrode interface is desirable. 4. Dead spots created by pressure flushing, from opposite sides of the workpiece, should be avoided. 5. A vent hole should be provided for any upwardly concave part of the tool-electrode to prevent accumulation of explosive gases. 6. A flush box is useful if there is a hole in the cavity
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Modern Manufacturing Methods Material removal rates In EDM the metal is removed from both the workpiece and the tool electrode. As can be seen from Fig. 5.12, the material removal rate depends not only on the workpiece material but on the material of the tool electrode and the machining variables such as pulse conditions,electrode polarity, and the machining medium. In this regard a material of low melting point has a high metal removal rate and hence a rougher surface. Typical removal rates range from 0.1 to 400 mm3 /min.
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Modern Manufacturing Methods The results of machining rates and surface roughness for different materials. And explain the effect of pulse energy (current) and duration on the crater size and hence the removal rate. The material removal rate, or volumetric removal rate (VRR), in mm3/min, was described by Kalpakjian (1997): VRR = (4 × 104) iTw 1.23 where i is the EDM current (A) and Tw is the melting point of the workpiece material (°C). Heat-affected zone Choosing electrodes that produce more stable machining can reduce the annealing effect. A finish cut removes the annealed material left by the previous high-speed roughing. The altered surface layer, which is produced during EDM, significantly lowers the fatigue strength of alloys.The altered layer consists of a recast layer with or without microcracks,some of which may extend into the base metal, plus metallurgical alterations such as rehardened and tempered layers, heat-affected zones, and intergranular precipitates. Generally, during EDM roughing, the layer showing icrostructural changes, including a melted and resolidified layer, is less than 0.127 mm deep, while during EDM finishing, it is less than 0.075 mm. Posttreatment to restore the fatigue strength is recommended to follow EDM of critical or highly stressed surfaces. There are several effective processes that accomplish restoration or even enhancement of the fatigue properties. These methods include the
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Modern Manufacturing Methods removal of the altered layers by low-stress grinding, chemical machining,and the addition of a metallurgical-type coating, reheat treatment, and the application of shot peening.
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  • Fall '12
  • JeraldBrevick
  • EDM, conventional machining processes, Jet Machining

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