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MMM LECTURE NOTES FINAL.pdf

3 production of tungsten carbide cutting tools

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3. Production of tungsten carbide cutting tools, fragile parts, and thin walled tubes. 4. Removal of fatigue cracks from steel structures under seawater. In such an application holes about 25 mm in diameter, in steel 12 to 25 mm thick, have been produced by ECG at the ends of fatigue cracks to stop further development of the cracks and to enable the removal of specimens for metallurgical inspection. 5. Producing specimens for metal fatigue and tensile tests. 6. Machining of carbides and a variety of high-strength alloys Advantages Absence of work hardening Elimination of grinding burrs Absence of distortion of thin fragile or thermo sensitive parts Good surface quality Production of narrow tolerances Longer grinding wheel life Disadvantages Higher capital cost than conventional machines Process limited to electrically conductive material Corrosive nature of electrolyte Requires disposal and filtering of electrolyte
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Modern Manufacturing Methods Chemical Machining (CM) Chemical machining (CM) is the controlled dissolution of workpiece material (etching) by means of a strong chemical reagent (etchant). In CM material is removed from selected areas of workpiece by immersing it in a chemical reagents or etchants; such as acids and alkaline solutions. Material is removed by microscopic electrochemical cell action, as occurs in corrosion or chemical dissolution of a metal. This controlled chemical dissolution will simultaneously etch all exposed surfaces even though the penetration rates of the material removal may be only 0.0025 0.1 mm/min. The basic process takes many forms: chemical milling of pockets, contours, overall metal removal, chemical blanking for etching through thin sheets; photochemical machining (pcm) for etching by using of photosensitive resists in microelectronics; chemical or electrochemical polishing where weak chemical reagents are used (sometimes with remote electric assist) for polishing or deburring and chemical jet machining where a single chemically active jet is used.
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Modern Manufacturing Methods CHM consists of the following steps: 1. Preparing and precleaning the workpiece surface. This provides good adhesion of the masking material and assures the absence of contaminants that might interfere with the machining process. 2. Masking using readily strippable mask, which is chemically impregnable and adherent enough to stand chemical abrasion during etching. 3. Scribing of the mask, which is guided by templates to expose the areas that receive CHM. The type of mask selected depends on the size of the workpiece, the number of parts to be made, and the desired resolution of details. Silk-screen masks are preferred for shallow cuts requiring close dimensional tolerances. 4. The workpiece is then etched and rinsed, and the mask is removed before the part is finished .
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Modern Manufacturing Methods Fig.,Contour cuts by CHM.
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  • Fall '12
  • JeraldBrevick
  • EDM, conventional machining processes, Jet Machining

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