The
grade of tooling materials to be used in the construction of a die casting die
should be
specified
as high quality, at a minimum, and preferable premium quality. These
requirements are based
on the extremely high temperatures and pressures used in die casting
production.
Tooling
grade requirements will vary depending on the tooling component, the alloy
being die cast, the
critical character of the cast part design and the long-term production
quantities desired. Every aspect
of the proposed product’s design and production specifications must be
discussed with the die caster
before tooling material can be selected. The following are typical tooling
lowest requirements:
Die and Cavity Materials
The
zinc alloys, which cast at the lowest temperature in the nonferrous family,
cause the least wear on their
tooling and thus permit the use of non-premium die material, such as P-20, in
cases where part designs
are relatively simple. Purchasers are cautioned, however, to be aware of the
unwise investment in
non-premium grade tooling for zinc parts if there is any possibility that
production quantities may reach
higher levels than originally anticipated. At higher production levels, such
tooling may expire and
the cost of replacement dies will far outweigh an original investment in
premium material.
Aluminum,
magnesium and ZA die casting dies require high quality tool steel, as above.
If
part designs have very critical features or if high production runs are being
contemplated,
however,
premium grade tooling will always be the wisest investment.
For
Al, Mg, ZA-12, and ZA-27 die cast parts, H13 Premium or Superior Grade tool
steel
is
recommended whenever part design features are intricate and specifications
tight, and when
production
volumes will be high. In such cases, non-premium grade tooling will nearly
always
result
in costly premature die failure.
Since
copper alloy die castings are cast at the highest temperatures of the
nonferrous alloys,
only
H13 high grade tool steel is recommended for brass die casting dies.
Metal
certifications for the material grades listed, provided by quality tooling
material suppliers,
will
be made available for inspection by the die caster. The H13 Premium or Superior
Grade should meet
the tool steel standard.Special Quality Die Steel and Heat
Treatment
Acceptance
Criteria for Die Casting Dies.
Die Cavity Insert Materials
The
materials recommended for use as tool steel for die cavity inserts parallel the
recommendations
for
die cavities, above, with some additions.
In
addition to H13 Premium or Superior Grade, the maraging and speciality tool
steels* are
used
for die inserts needing higher hardness to improve their resistance to the heat
checking
(thermal
fatigue cracking) or crazing of the insert’s surface caused by thermal cycling
of the
die
from the high temperature molten alloy and die spray/die cooling. The fine
cracks that may
result
can produce corresponding veins on castings.
In
high wear (erosion/washout) and temperature areas, especially if internal
cooling and/or die
spray
is difficult, small cores and inserts in aluminum die casting dies can
eventually break or
wash
away due to the velocity of the aluminum entering the cavity. Tungsten- and
molybdenum based alloys
are occasionally used successfully in these areas to resist these conditions.
Although these
materials show superior physical properties compared to conventional steels at
high working
temperatures, care must be used in machining them. Also, their increased cost
must be considered in
the overall cost of the die and number of shots required (life of the die).
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