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CLC Production Bay
In addition to dissolved/dispersed solids, there are other
On the other end, for our customers working with
common contaminants that are found in used EDM oil.
ing, there is an impact that is of concern. Regardless
Water is perhaps the most insidious contaminant; often
of the aerospace OEM, there are cutting settings that
introduced as mist suspended in compressed air used to
are locked in. Metallurgical analysis of the workpiece
blow off the workpiece, or in air introduced to the oil on certiﬁ ed processes, such as aerospace manufactur-
and annual equipment calibration is intended to assure
machines that use compressed air to ﬁ ll the work tank.
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that quality parts are being made. However, there is a
Water contamination will eventually lead to rust/corro-
sion issues, oil degradation, and increased acid number.
potential loss of productivity. Based on the chemical
makeup of the contaminant, the impact of high particu-
To this point, we talked about the various changes in oil
late concentration could be a lowering of the dielectric
due to contamination, but what is the result to the EDM
strength. This means that the gap will ionize at greater
process? The major effect of contaminated, used EDM
distance from the workpiece, potentially losing valuable
oil is the impact on dielectric strength. This is often
cutting energy. Conversely, the impact could be a higher
confused with dielectric constant, but there is an
dielectric strength which would cause the gap to ionize
important difference. Dielectric constant, also called
closer to the workpiece. In this case, the closer phys-
relative permittivity, is the ratio of an insulating
material’s capacitance to the capacitance of a vacuum.
reducing the metal removal rate. Yes, adjusting process
This constant is a unitless number that represents a
parameters will keep the end result where it should be,
materials ability to store electrical energy. ical distance could adversely affect ﬂ ush conditions,
but at a loss of productivity.
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Dielectric strength, however, is a measure of a material’s
As EDM operators know, there are process settings
insulating property. An increasing voltage is applied
that work within the “sweet spot.” Be it ﬂ ush pressure,
across two electrodes until the insulating material breaks capacitance, or Off-Time, there is an ideal middle range
down and a spark is detected between the two elec-
that achieves maximum productivity. A change in
trodes. For insulating liquids, the test result is typically
dielectric strength will change the sweet spot and
given as the breakdown voltage (with a speciﬁ ed gap of
impact productivity.
0.1” [2.5mm]) in the units KV.
At another level, the contamination will impact the
We have some customers who have never changed their
oil in over 30 years of operation. They simply add new oil
generally not tested and its impact is unknown. Based on
to replace what was lost in the process or through evap-
the exact contaminate makeup, there is possibility that it
oration. They say their equipment cuts ﬁ ne. For some, chemistry of the recast layer. This is something that is
could be a factor in microcracking.
that is true. If the EDM is used at 100+ amps to cut large
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EDM Today Magazine EDM Today Magazine EDM Today, Fall 2023 Issue
forging dies, they will see little impact even with fairly
high levels of contamination and AN.
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