Electrochemical Machining ECM

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Electrochemical Machining (ECM)

• Dr. Lotfi K. Gaafar

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Electrochemical Machining
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Electrochemical Machining

• Uses an electrolyte and electrical current to
  ionize and remove metal atoms
• Can machine complex cavities in high-strength
  materials
• Leaves a burr-free surface
• Not affected by the strength, hardness or
  toughness of the material

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Electrochemical Machining
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Operating Principle

• As the tool approaches the work piece it erodes
  the negative shape of it. Thus complex shapes
  are made from soft copper metal and used to
  produce negative duplicates of it. This process
  is called electrochemical sinking

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Operating Principle

• The tool may also be connected to a CNC machine
  to produce even more complex shapes with a single
  tool.

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Operating Principle

• Several tools may be joined to provide a fast
  broaching technique on hardened material.
• Conventional machines may be easily changed to an
  ECM and is a common practice.

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Main Subsystems

• The power supply.
• The electrolyte circulation system.
• The control system.
• The machine.

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ECM Components (Power)

• The power needed to operate the ECM is obviously
  electrical. There are many specifications to
  this power.
• The current density must be high.
• The gap between the tool and the work piece must
  be low for higher accuracy, thus the voltage must
  be low to avoid a short circuit.
• The control system uses some of this electrical
  power.

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ECM Components (electrolyte circulation system)

• The electrolyte must be injected in the gap at
  high speed (between 1500 to 3000 m/min).
• The inlet pressure must be between 0.15-3 MPa.
• The electrolyte system must include a fairly
  strong pump.
• System also includes a filter, sludge removal
  system, and treatment units.
• The electrolyte is stored in a tank.

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ECM Components (control system)

• Control parameters include
• Voltage
• Inlet and outlet pressure of electrolyte
• Temperature of electrolyte.
• The current is dependant on the above parameters
  and the feed rate.

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ECM Components (Machine)

• The machine is a major subsystem of the ECM.
• It includes the table, the frame, work enclosure
  (prevents the electrolyte from spilling), the
  work head (where the tool is mounted)
• The tools (electrodes) are also part of the
  machine system

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Advantages

• There is no cutting forces therefore clamping is
  not required except for controlled motion of the
  work piece.
• There is no heat affected zone.
• Very accurate.
• Relatively fast
• Can machine harder metals than the tool.

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Advantages over EDM

• Faster than EDM
• No tool wear at all.
• No heat affected zone.
• Better finish and accuracy.

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Disadvantages

• More expensive than conventional machining.
• Need more area for installation.
• Electrolytes may destroy the equipment.
• Not environmentally friendly (sludge and other
  waste)
• High energy consumption.
• Material has to be electrically conductive.

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Applications

• The most common application of ECM is high
  accuracy duplication. Because there is no tool
  wear, it can be used repeatedly with a high
  degree of accuracy.
• It is also used to make cavities and holes in
  various products.
• Sinking operations (RAM ECM) are also used as an
  alternative to RAM EDM.
• It is commonly used on thin walled, easily
  deformable and brittle material because they
  would probably develop cracks with conventional
  machining.

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Economics

• The process is economical when a large number of
  complex identical products need to be made (at
  least 50 units)
• Several tools could be connected to a cassette to
  make many cavities simultaneously. (i.e. cylinder
  cavities in engines)
• Large cavities are more economical on ECM and can
  be processed in 1/10 the time of EDM.

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Products

• The two most common products of ECM are
  turbine/compressor blades and rifle barrels. Each
  of those parts require machining of extremely
  hard metals with certain mechanical
  specifications that would be really difficult to
  perform on conventional machines.
• Some of these mechanical characteristics achieved
  by ECM are
• Stress free grooves.
• Any groove geometry.
• Any conductive metal can be machined.
• Repeatable accuracy of 0.0005.
• High surface finish.
• Fast cycle time.

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Safety Considerations

• Several sensors are used to control short
  circuit, turbulence, passivation, contact and
  overcurrent sensors. In case of contact, immense
  heat would be generated melting the tool,
  evaporating the electrolyte and cause a fire.
• The worker must be insulated to prevent
  electrocution.
• The tool and the work piece must be grounded
  before any handling is performed.

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Safety Consideration

• Hydrogen gas emitted is very flammable, so it
  should be disposed of properly and fire
  precautions should be taken.
• The waste material is very dangerous and
  environmentally unfriendly (metal sludge) so it
  must be recycle or disposed of properly.
• Electrolyte is highly pressurized and worker must
  check for minor cracks in piping before
  operating.

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Pulsed Electrochemical Machining

• A form of electrochemical machining the current
  is pulsed to eliminate the need for high
  electrolyte flow
• Improves fatigue life of the part

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Electrochemical Grinding

• Uses a rotating cathode embedded with abrasive
  particles for applications comparable to milling,
  grinding and sawing
• Most of the metal removal is done by the
  electrolyte, resulting in very low tool wear
• Adaptable for honing

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Electrochemical Grinding