| Purpose: Metal
removal, remove stress risers, corner rounding, edge sharpening,
deburring, providing high luster, removing heat effected zones
and micro-cracks, and often improves the products fatigue life.
Process: The
NNI EP process utilizes various engineered blends
of acids that are designed to dissolve the components
of the part’s material, when the part is
connected to a positive electrical charge, placed
in a bath of engineered acids, in the presence
of a negatively charged counterpart, miracles can
happen. The part then becomes the anode, the counterpart
becomes the cathode. Ions flow from the part to
the cathode, in a somewhat disproportionate manner.
The irregularities such as corners, burrs, and
protrusions become high current density areas,
these polish the fastest. Low areas or middle areas
polish slower. ID’s will only polish if there
is exposure to a cathode.
During polishing, the acids become saturated with the dissolved metals
and metal salts from the parts that have been polished. During repeated
use, the solution approaches its equilibrium point and then begins precipitating
out additional metals and salts to the bottom of the EP system as sludge.
The majority of the metal in the solution plates to the cathode.
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Considerations:
- Oxygen
is liberated at the anode, and hydrogen is liberated
at the cathode. Therefore, EP will not cause hydrogen
embrittlement of the parts.
- EP
can improve fatigue life by removing cold working
stresses, or heat effected zones on the cut surfaces,
smoothing stress risers, removing micro-cracks, and
rounding corners.
- NNI
can also modify the EP effect to sharpen edges and
points.
- The
EP effect when done properly, can improve a finish
typically 2 fold, or more if tolerances allow. i.e.,
a 8Ra will be reduced to a 4Ra.
- Proper
EP can greatly reduce the possibility of bacterial
growth on critical surfaces.
- An
area to attach the rack should be identified prior
to RFQ.
- Typically,
part designers target .0008” to .0010” inch
removal per surface, if maximum fatigue life of the
product is a concern.
- Parts
typically need to be back figured by NNI engineering
to allow for the material that the customer’s
design requirement needs to be removed.
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