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Manufacturing Processes > Non-Traditional Machining > Electrochemical Machining

 

Electrochemical Machining(ECM)

 

Process description

Workpiece material is removed by electrolysis. A tool, usually copper (-ve electrode), of the desired shape is kept a fixed distance away from the electrically conductive workpiece (+ve electrode), which is immersed in a bath containing a fast flowing electrolyte and connected to a power supply. The workpiece is then dissolved by an electrochemical reaction to the shape of the tool. The electrolyte also removes the ‘sludge’ produced at the workpiece surface.

Materials

Any electrically conductive material irrespective of material hardness, commonly, tool steels, nickel alloys and titanium alloys. Ceramics and copper alloys are also processed occasionally.

ECM

Process variations

  • Electrochemical Grinding (ECG): combination of electrochemical reaction and abrasive machining of workpiece.
  • Electrochemical drilling: for the production of deep, small diameter holes.
  • Electrochemical polishing: for deburring and honing.

Economic considerations

  • Production rates moderate.
  • Material removal rates typically 50–250mm²/s.
  • Linear penetration rates up to 0.15 mm/s.
  • Dependent on current density, electrolyte and gap between tool and workpiece.
  • High power consumption.
  • Lead time can be several weeks. Tools are very complex.
  • Setup times can be short.
  • Material utilization very poor. Scrap material cannot be recycled.
  • Disposal of sludge and chemicals used can be costly and hazardous.
  • High degree of automation possible.
  • Economical for moderate to high production runs.
  • Tooling costs very high. Dedicated tooling.
  • Equipment costs generally high.Direct labor costs low to moderate.

Typical applications

  • Hole (circular and non-circular) production, profiling and contouring of components
  • Engine casting features
  • Turbine blade shaping
  • Dies for forging
  • Gun barrel rifling
  • Honeycomb structures and irregular shapes
  • Burr free parts
  • Deep holes

Design aspects

  • High degree of shape complexity possible, limited only by ability to produce tool shape.
  • Can be used for material susceptible to heat damage.
  • Suitable for small diameter, deep holes with length to diameter ratios up to 50:1.
  • Suitable for parts affected by thermal processes.
  • Undercuts possible with specialized tooling.
  • Possible to machine thin and delicate sections due to no processing forces.
  • Cannot produce perfectly sharp corners.
  • Minimum radius =0.05 mm.
  • Minimum hole size =Ø0.1 mm.

Quality issues

  • Burr free part production.
  • Produces slightly tapered holes, especially if deep, and some overcut possible.
  • Finishing cuts are made at low material removal rates.
  • Deep holes will have tapered walls.
  • No stresses introduced, either, thermal or mechanical.
  • Virtually no tool wear.
  • Arcing may cause tool damage.
  • Some electrolyte solutions can be corrosive to tool, workpiece and equipment.
  • Surface detail good.
  • Surface roughness values ranging 0.2–12.5 µm Ra. Dependent on current density and material being machined.
  • Achievable tolerances ranging ±0.013–±0.5mm. (Process capability charts have not been included. Capability is not primarily driven by characteristic dimension but by the material being processed.)

costing