Page 53 - EDM Today Winter 2025

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PROS AND CONS OF ECM
exploit the double layer effect (see [5]) to machine micro
parts with exceptional precision. In this case, pulses of
Firstly, ECM is ideally suited for certain production appli-
microseconds are used.
cations. The tool electrode must be optimized through
The STEM (shaped tube electrolytic machining) process,
trial and error, although modelling and simulation can
assist. Once defi ned, the tool electrode experiences no
which uses a tube electrode insulated on the outside, can
wear, allowing for the production of many parts.
A crucial requirement is maintaining good, constant
Since ECM targets sharp geometries fi rst, it is also
pressure fl ushing in the gap. Short circuits must be produce drilled holes with high productivity.
widely used for deburring, with lower current densities.
avoided, as currents of hundreds of amperes could Another notable application is dressing and truing
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destroy the tool electrode. ECM offers higher productivity
metal-bonded diamond and CBN grinding wheels, called
than EDM die sinking, with excellent surface quality even
electrochemical dressing (ECD).
in the roughing stage, as high current density yields the
best results. Since it takes current density to obtain a
Effi cient dressing of this kind of grinding wheels is gener-
good surface (50 to 150 A/cm2), the feedrate is “almost
ally problematic since the metal bonding is very resistant
independent” from the active area to be machined
to wear. The ECD process removes ground particles
(typically 1-3 mm/min).
from the wheel and enhances the protrusion of diamond
grains by removing the binding phase, all done in-process
The rounding effect of ECM is not a drawback for many
applications.
Although theoretically possible, combining EDM and
The resulting surface has no heat-affected zone, no
ECM processes in a single machine to leverage the bene-
tensile stress, and no microcracks. Benchmark tests with (see Fig. 11).
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fi ts of both technologies has only been tested in research
other machining methods (laser, EDM, grinding) show
settings [10]. The main challenge lies in the technological
that ECM-machined parts have a longer fatigue life.
liquid required: ECM needs an electrolyte, while EDM re-
quires a dielectric. This creates a paradox, similar to “dry
However, caution is needed regarding the electrolyte.
water” or “deafening silence,” since a liquid cannot both
The electrolyte parameters control is very important in
conduct (electrolyte) and insulate (dielectric) electricity.
ECM. Varying electrolyte conductivity and temperature
For some applications, a more practical approach is to
and fl ow fi eld disturbing phenomena can affect the
fi rst use a Die Sinking machine for EDM, followed by
accuracy of the process.
The most common electrolytes are aqueous solutions of
constraints. However, this method requires addressing
NaNO3 (about 12 to 20%) or NaCl. During the process,
the accuracy issues that arise from unclamping the
ions of iron, nickel, and titanium form hydroxides that can another machine for ECM, to achieve stringent surface
workpiece between processes.
be easily fi ltered. Unfortunately, chromium partially dis-
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Other variants have been investigated by the scientifi c
solves, forming hexavalent chromium ions (CrVI), which
are carcinogenic and toxic. Traditional methods cannot
community, but their description is beyond the scope of
fi lter these ions. They must be reduced using FeSO4 or
this article:
NaHSO3 and HNO3, then precipitated with NaOH to form
- Jet electrochemical machining (JECM), where the
non-toxic trivalent chromium (CrIII) or removed using
electrolyte is pumped through a nozzle to form a jet
activated carbon and scrap iron. [4]
- WECM (wire ECM), used for machining micro structures
APPLICATIONS
As mentioned, ECM machining (sinking) is widely used in - Ultrasonic assisted EDM, to improve the fl ushing
production applications, such as electric shaver heads,
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medical technologies, and aerospace, for producing
parts with very low roughness and no heat-affected zone.
In many cases, no after treatment of the part is needed,
since there is no particle adhesion on the workpiece.
An interesting aspect of ECM, being a “cold” process, is
that the electrode can be created using galvanoplastic
methods or non-metallic 3D printing, then coated with a
conductive layer. This allows, e.g., a fi ngerprint pattern to
be copied into steel (see Fig. 10).
Much like EDM, ECM is scalable, from machining of large Fig. 7: Machining setup for a turbine blade [2]
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parts to micro ECM. By using very short pulses, ECM can
(Continued on next page)
51
EDM Today, Winter 2025 Issue