MMM LECTURE NOTES FINAL.pdf

Application of edm the edm process has the ability to

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Application of EDM The EDM process has the ability to machine hard, difficult-to-machine materials. Parts with complex, precise and irregular shapes for forging, press tools, extrusion dies, difficult internal shapes for aerospace and medical applications can be made by EDM process. Some of the shapes made by EDM process are shown in Figure 3.
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Modern Manufacturing Methods The material removal rate, MRR, in EDM is calculated by the following foumula: MRR = 40 I / T m 1.23 (cm 3 /min) Where, I is the current amp, T m is the melting temperature of workpiece in 0 C EDM electrodes Material. Metals with a high melting point and good electrical conductivity are usually chosen as tool materials for EDM. Graphite is the most common electrode material since it has fair wear characteristics and is easily machinable and small flush holes can be drilled into graphite electrodes. Copper has good EDM wear and better conductivity.It is generally used for better finishes in the range of 0.5 μm Ra .Copper tungsten and silver tungsten are used for making deep slots under poor flushing conditions especially in tungsten carbides. It offers high machining rates as well as low electrode wear. Copper graphite is good for cross-sectional electrodes. It has better electrical conductivity than graphite while the corner wear is higher. Brass ensures stable sparking conditions and is normally used for specialized applications such as drilling of small holes where the high electrode wear is acceptable. Movements.
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Modern Manufacturing Methods In addition to the servo-controlled feed, the tool electrode may have an additional rotary or orbiting motion. Electrode rotation helps to solve the flushing difficulty encountered when machining small holes with EDM. In addition to the increase in cutting speed, the quality of the hole produced is superior to that obtained using a stationary electrode. Electrode orbiting produces cavities having the shape of the electrode. The size of the electrode and the radius of the orbit (2.54-mm maximum) determine the size of the cavities. Electrode orbiting improves flushing by creating a pumping effect of the dielectric liquid through the gap. Polarity. Electrode polarity depends on both the work piece and electrode materials. Electrode wear. The melting point is the most important factor in determining the tool wear. Electrode wear ratios are expressed as end wear, side wear, corner wear, and volume wear as shown in given figure. The term no wear EDM occurs when the electrode-to-work piece wear ratio is 1 percent or less. Electrode wear depends on a number of factors associated with the EDM, like voltage, current, electrode material, and polarity. The change in shape of the tool electrode due to the electrode wear causes defects in the work piece shape. Electrode wear has even more pronounced effects when it comes to micromachining applications. The corner ratio depends on the type of electrode. The low melting point of aluminium is associated with the highest wear ratio. Graphite has shown a low tendency to wear and has the possibility of being molded or
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  • Fall '12
  • JeraldBrevick
  • EDM, conventional machining processes, Jet Machining

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