Electrical Methods of Material Removal

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Electrical Methods of Material Removal

• Chapter 5

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EDM Electric Discharge Machining

• The process of removing metal with an electric
  arc.
• Store energy in a capacitor and then discharge to
  create an electric arc between the work piece and
  an electrode many times a second.
• Immersed in a moving insulated fluid, called
  Dielectric, an important part of the process.
• Perform operations that are nearly impossible to
  do any other way.
• The action is described as erodes.
• Slow process

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General Principals of EDM

• Electrode (Graphite, Copper, Brass, etc.)
• Electrical arc (Bridges the gap)
• Moving fluid
• Automatic sensor
• Cavity conforms to electrode
• Control over the cut
• Material removal rate
• Surface Roughness

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Advantages of EDM

• Hardness of material does not matter.
• Fragile parts can be machined without warping or
  damaging from the force of tools.
• Holes complex shapes can be made.
• Easy to automate
• Very fine surface finish and tolerances.
• No Burrs

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Disadvantages of EDM

• Slow process which results in higher cost per
  pound of material removal.
• Cost of machine
• Space required
• Environmental conditions required
• Elaborate filtration systems
• Removal of spent fluid

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Operating Principles
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Types of EDM

• Ram EDM
• Wire EDM
• Electric Discharge Grinding
• Electrochemical Grinding

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RAM EDM
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RAM EDM

• Vertical position controlled by hydraulic ram
• Die sinking
• Plunge EDM
• Electrodes
• Clamp work piece
• Position electrode
• Set amperage and depth
• Wear rates (Roughing finishing)
• Orbiting (Undercuts, Threads)
• CNC

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Bench Top RAM EDM
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Hole Driller EDM
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Tap Remover EDM
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Wire EDM Machine
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Wire EDM

• Electrode (Wire .002 - .010)
• Only use edge once
• More complex shapes than RAM EDM
• Automatic wire feed
• Can run unattended
• Can make whole part in one setup
• Several passes (Rough, Finish)
• CNC

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Wire EDM (Cont.)

• Greater repeatability than conventional machining
  techniques.
• Frequently used for Polishing, Final dressing to
  dimensional tolerances, called skimming.

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Wire EDM Machine
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Electrical Discharge Grinding

• Bench grinder with a grinding wheel replaced by
  an electrode.
• Same advantages as other EDM.
• Grinding wheel can be fairly complex.

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Electrochemical Grinding

• Resembles EDG.
• Surface chemically treated to loosen grains of
  metal.
• Accelerated by passing current through solution.
• Loosened grains removed by conventional grinding
  wheel.
• Less force resulting in less heat.