Aerospace & Defense Technology - October 2021 - 22

Engine Technology
OEM aerospace components can be repaired and restored back to 'as new' or better through selective electroplating.
suming
than simply manufacturing a new
part. In the aerospace industry, downtime
can be costly, making it vital that remanufacturing
can be carried out both efficiently
and effectively. Here, selective
electroplating offers a vital benefit.
Selective plating (also known as brush
plating) is a method of repairing and
restoring critical dimensions and surface
properties of worn components to OEM
standards. The process can be used to treat
specific areas of a component, with accurate,
selective brush plating of materials
onto localized surfaces and diameters. As
well as typically being faster than alternative
surface coating methods, selective
plating can be completed on-site, reducing
the downtime and cost associated with
disassembly, transport, and reassembly.
Given the continuous use and harsh
environments experienced when aerospace
equipment is in operation, selective
plating needs to bond at the atomic
level. This is something not provided by
traditional surface coating methods,
such as thermal spray, which only
forms a mechanical bond.
To create this atomic bond, selective
plating uses electrochemical principles.
An electrolyte solution, containing ions
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of the deposit material, is introduced between
the negatively charged plating surface
and the positively charged tool.
When the tool - or anode - touches the
surface, a circuit is created, with a cover
material around the tool providing a
reservoir to ensure even distribution. The
current within the circuit causes the ions
between the interfaces to bond, building
up the plating layer and delivering a
highly adherent and dense metal deposit.
The range of metals used in selective
plating is extensive. The process is suitable
for applying any metals that are traditionally
applied by tank electroplating,
the most common being cadmium,
zinc-nickel, nickel, copper, cobalt,
nickel-tungsten, cobalt-chromium carbide,
silver, gold, and platinum. The
SIFCO Process® can be carried out manually,
it can be mechanized, or it can be
automated for higher volume applications
- something not traditionally associated
with selective plating.
Benefits of Selective Plating Over
Tank Plating
Selective plating is already approved
worldwide by most major airlines, landing
gear and engine manufacturers, and
www.aerodefensetech.com
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is specified in overhaul manuals and
standard practice manuals. SIFCO ASC
works closely with customers in the
aerospace industry to offer practical,
cost-effective options for repairing and
enhancing the surfaces of components.
For example, when looking to remanufacture
a turbine interstage case from a
PW100 engine, an OEM customer explored
tank plating and brazing options,
before opting for selective electroplating.
With an internal diameter of
5.625 " , a specified plating thickness of
0.003 " using AeroNikl® 250, and limited
access to the area that needed plating,
precision was key to success.
Tank plating - often used for this type
of application - requires extensive masking.
As well as being a labor-intensive and
time-consuming process that often incurs
additional delays shipping the part to outside
vendors, tank plating can also require
post-plating machining due to edgebuild-up.
Selective plating allows for more
accurate control of deposit thicknesses - a
point crucial to meeting the specification
- allowing the part to be plated to size
with no post-machining. With the
process taking place at room temperature,
the risk of part distortion is also reduced.
For this particular component, selective
plating also offered a far quicker
turnaround, with processing times reduced
from one-to-two days to approximately
just two hours. With the
portable nature of brush plating, repairs
can be undertaken either in the shop or
on the job site - offering process flexibility
as well as reducing the impact of
external delays and shipping.
Reducing Scrappage and Rework
In the aerospace industry, in particular,
the very low design tolerance of
manufactured components can result in
scrappage due to production defects and
strict quality control. Again, selective
plating can help overcome this issue, offering
a way to swiftly rework parts to
ensure that they meet specifications.
When working with an OEM for the
aerospace industry, SIFCO ASC was able
to specify selective plating to rework a
part to avoid the need to strip and replate
it. The component in question
was an outer ring flange for a turbine jet
engine shaft. As part of the original
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Aerospace & Defense Technology - October 2021

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