MMM LECTURE NOTES FINAL.pdf

Chm applications range from large aluminium airplane

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CHM applications range from large aluminium airplane wing parts to minute integrated circuit chips. The practical depth of cut ranges between 2.54 to 12.27 mm. Shallow cuts in large thin sheets are of the most popular application especially for weight reduction of aerospace components. Multiple designs can be machined from the same sheet at the same time. CHM is used to thin out walls, webs, and ribs of parts that have been produced by forging, casting, or sheet metal forming, as Further process applications related to improving surface.
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Modern Manufacturing Methods characteristics include the following: 1. Elimination of alpha case from titanium forgings and super plastic formed parts 2. Elimination of the decarburized layer from low alloy steel forgings 3. Elimination of the recast layer from parts machined by EDM 4. Removal of sharp burrs from conventionally machined parts of complex shapes 5. Removal of a thin surface from forgings and castings prior to penetration In section below the surface (required for the detection of hidden defects). Fig., Thinning of parts by CHM
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Modern Manufacturing Methods UNIT-IV Electro discharge Machining(EDM) Introduction The history of electrodischarge machining (EDM) dates back to the days of World Wars I and II when B. R. and N. I. Lazarenko invented the relaxation circuit (RC). Using a simple servo controller they maintained the gap width between the tool and the workpiece, reduced arcing, and made EDM more profitable. Since 1940, die sinking by EDM has been refined using pulse generators, planetary and orbital motion techniques,computer numerical control (CNC), and the adaptive control systems.During the 1960s the extensive research led the progress of EDM when numerous problems related to mathematical modeling were tackled.The evolution of wire EDM in the 1970s was due to the powerful generators,new wire tool electrodes, improved machine intelligence, and better flushing. Recently, the machining speed has gone up by 20 times,which has decreased machining costs by at least 30 percent and improved the surface finish by a factor of 15. EDM has the following advantages. 1. Cavities with thin walls and fine features can be produced. 2. Difficult geometry is possible. 3. The use of EDM is not affected by the hardness of the work material. 4. The process is burr-free. Mechanism of material removal
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Modern Manufacturing Methods In EDM, the removal of material is based upon the electrodischarge erosion (EDE) effect of electric sparks occurring between two electrodes that are separated by a dielectric liquid as shown in above fig., Metal removal takes place as a result of the generation of extremely high temperatures generated by the high-intensity discharges that melt and evaporate the two electrodes. A series of voltage pulses of magnitude about 20 to 120 V and frequency on the order of 5 kHz is applied between the two electrodes, which are separated by a small gap, typically 0.01 to 0.5 mm. When using RC generators, the voltage pulses, shown in Fig. 5.3,are responsible for material removal .
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  • Fall '12
  • JeraldBrevick
  • EDM, conventional machining processes, Jet Machining

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