Home » Engraved Versus EDM
20% Longer Stamp Life
The value of a Marking Die is composed of:
- 1. The Initial Cost
- 2. The Service Life
- 3. Cost of Production (rework, scrapped work, downtime)
The basic difference
between
an Engraved
Die and one made by EDM (Electrical
Discharge
Machining)
involves how material
is removed
to form characters
and designs.
EDM
uses
a high
frequency
electrical
discharge
to erode
away-unwanted
material
leaving
the desired
characters
or design.
Due
to the EDM's
intense
local
heat
(up
to 10,OOO;c)
the cavity
surface
is structurally
changed
to a depth
up to 0.005. As this
surface
layer
is untempered,
premature
failure
may
occur
when
these
dies
are either
subjected
to stress
cycling;
high
impact
or tensile
stresses
are
encountered.
These
stresses
remain
in the finished
product
and
can cause
short
die life and
or failure.
Obviously
the smaller
the character
the greater
the negative
effect
these
stresses
have
on the die's
life and performance.
As the surface
layer
is structurally
changed
so is the subsurface.
The
intense
heat
creates
3 layers
(see
fig. 1). The
top layer
(EDM
surface
layer)
is created
when
the displaced
molten
metal
and
small
amounts
of electrode
material
form
spheres
and
is strewn
over
the work
metal's
surface.
The
middle
layer
is the recast
layer. The EDM
process
has
literally
altered
the
work
metal's
metallurgical
structure
and
characteristics
in the recast
layer.
Due
to the displaced
molten
metal's
rapid
quenching,
micro
cracks
can
form
in
this
very
hard,
brittle
layer. Left
untreated
the affects
of this layer
can cause
premature
failure.
Layers
formed
by
the EDM
process
The
annealed
layer
(last
layer)
has
only
been
heated
as opposed
to melted.
The power
used
for the cut combined
with
the heat
sinking
ability
of the material
regulates
the depth
of both
the layer
and
that
of the heat
effected
zone.
An Engraved
Die
is cut without
incurring
temperatures
that
would
change
the metallurgical
properties
of the metal
and
avoids
creating
any
stresses.
Being
engraved
these
dies
will have
finer
detail
and
produce
a cleaner,
more
precise
mark. Heat-
treating
after
the final
engraving
ensures
the die has
uniform
metallurgy
and
will hold
up under
repeated
use
and
deliver
a
longer
service
life.
The
math
is simple. You
get the most
bang
with
engraving.