Finishing - September-October 2020

12 POWDER COATING
Selectively speaking
Damage to molds and related tooling for
plastic and metal parts seems to be
inevitable due to foreign object damage,
acidic corrosion, and other causes of wear and
tear. In some cases, small flaws in new mould
tooling causes higher than acceptable scrap
rates. This can mean tearing down the
equipment, removing the mould, and sending
it out for repairs. However, with in-situ
selective plating, mould surfaces can often be
repaired without taking the mould out of the
machine. This greatly reduces repair costs.
The end result is reduced rework and scrap
rates.
Selective Plating Process
Mould and die costs vary widely depending
on size, materials and origin. With costs
ranging from tens of thousands of dollars up
to millions, the last thing a manufacturer
wants to do is buy new tooling. Just the cost
of removing a mould from the machine for
outside repair is substantial, and the cost of
lost production is greater still. These costs vary
depending on the size and depth of the
mould area needing repair. This makes typical
in-situ plating repairs for a one-day job a very
attractive option.
As a general rule, defect depths of up to
about 0.060” are good candidates for this
type of repair. Greater depths are possible and
the decision to proceed with deeper defects
may become an economical one and not
technical. Very large or deep defects can often
be prepared for selective plating by peening
or filling with a metal plug to minimize the
time needed for plating.
If a mould has a lot of corrosion, scratches
and other small surface flaws that result in a
poor finish on the molded part, the
temptation may be to remove the tooling and
send it out for tank electroplating. However,
selective plating can take care of these flaws
without extensive masking and is significantly
faster than tank electroplating.
The general approach for a selective plating
repair is:
• Dish out the repair area to create the
appropriate depth to-diameter ratio
• Apply cleaning and surface treatment
chemicals to prepare for plating
• Use selective plating to fill the depression
with filler metal material (often copper)
• Then selectively plate with a hard cap
metal that matches the performance
requirements of the tool
continues on p14
Finishing - September/October2020