Page 51 - EDM Today Winter 2025

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be removed (anode) donates electrons and passes over
to the electrolyte solution as an ion. Depending on the
chemical properties of the metal ions and the composi-
tion of the electrolyte solution, the metal ions are either
dissolved or react with components of the electrolyte,
e.g., causing the formation of metal hydroxides. These
are not soluble in the electrolyte solution and fall out,
whereby the removal of the material is made possible
with simple separation processes. Hydrogen ions, on the
other hand, are discharged at the cathode. So, there is
dissolution of the anode, whereas the tool electrode has
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absolutely no wear.
It is important to note that the rate of dissolution is
not infl uenced by the metal hardness, similarly to what
happens for EDM.
Fig. 1: Classifi cation of the ECM processes according
Another relevant observation is that the process tem-
to the directive VDI 3401
perature is about 35 °C, and not about 10,000 °C as in
EDM. This has a lot of implications as far as the surface
THE PRINCIPLE
When an electric current fl ows between two conductors
in an electrolyte (a conductive liquid), the process is quality is concerned.
known as electrolysis. The positive electrode is called
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the anode, and the negative electrode is the cathode.
The formulas describing ECM are quite simple:
In the electrolyte, electricity is carried by ions—atoms
Where:
that have lost or gained electrons—unlike in a metallic
m……..removed mass on the anode side [g]
wire where electricity is carried by electrons. Positively
M……..molar weight [g/mol]
charged ions move towards the cathode, while negatively
I………current [A]
charged ions move towards the anode.
t………machining time [sec]
z………electrochemical valence change (e.g., for the
As shown in Fig. 1, this principle has various applica-
reaction: Fe Fe2+ + 2e‾ follows z = 2)
tions, such as deburring or polishing, depending on the
Vsp……specifi c removal volume
current density.
ρ …. Density
Fig. 2 illustrates the process: F……...Faraday constant (96487 A·sec/mol)
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For a specifi c material, we defi ne the specifi c
removal vsp

and we obtain the simple formula:
Where:
V is the removed volume [mm3]
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I = average current [A]
t = machining time [min]
Another very important formula to consider is:

Fig. 2: ECM principle

The positive pole of a voltage source is connected to the
metal workpiece (anode), the negative pole to a metal
cathode (the tool electrode). Between the two electrodes
there is a conducting medium, usually an NaNO3 or NaCl
s = gap size
watery solution. The distance between the electrodes
vf = feed rate
is about 0.01-1 mm. By applying a voltage, complicated Where: (Continued on next page)
k = electrolyte conductivity
electrochemical reactions take place. The metal that is to
U = source voltage
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dU = polarisation voltage
EDM Today, Winter 2025 Issue
49