Electrochemical Machining (ECM)
Posted on 16-03-2010Electrochemical Machining (ECM)
Electrochemical Machining is an unconventional metal machining technology based on electrolysis in which the product (workpiece) is connected in an electrical circuit as anode and the tooling (electrode) as cathode. In electrochemical machining the product is processed without contact or any thermal influence.
The workpiece, that has to be electrical conductive, is dissolved locally by electricity (Electro) and chemistry (Chemical) until it reaches the required complex 3D end shape.
The tool (electrode) is placed close to the workpiece and in the gap between the tool and the workpiece an electrolyte is flushed for the conductance of the current and for the removal of reaction products like metal hydroxides, gas and heat.
The highest current density is reached at places where the tool is the closest to the workpiece; the shape of the tool is copied in the workpiece.
The desired anodic reaction at the workpiece is the dissolution of metal to metal ions.
Me -> Men+ + n e-
Other side reactions are possible at the anode, leading to a lower current efficiency, for example the oxidation of water:
2H2O -> 4H+ + O2 + 4 e-
During electrochemical machining the reaction at the cathode usually is the reduction of water, leading to the evolution of hydrogen gas:
2H2O + 2 e- -> 2OH- + H2
In the electrolyte bulk the metal ions can react with the hydroxyl ions to form metal hydroxides. Whether the metal ions react to metal hydroxides depends on the type of metal ions and the properties of the electrolyte (pH).
Men+ + n OH- -> Me(OH)n
The metal hydroxides can be removed from the electrolyte by, for example, micro filtration.
The current through the electrolyte in the working gap is conducted by the anions and cations in the electrolyte.
The temperature of the electrolyte increases by the movement of the ions, this is called Joule heating.