Casting
versatility leads to further savings.
Die
Casting
Die
casting is the most efficient process for high volume precision casting,
producing the best tolerances and rapid production rates, but having high
initial tooling costs.
Die
casting should be considered for components requiring a production run of at
least 10,000 pieces. All tolerances depend on part size and complexity;
however, tolerances of ±0.001" are common. Hot chamber die casting cycle rates
range from roughly 150 parts per hour for large components to over 2,000 per
hour for small ones.
The
ZAMAK die casting alloys and ZA-8 can be used in a "hot chamber" die casting
machine, while ZA-12 and ZA-27 must be "cold chamber" die cast like the
aluminum alloys. The hot chamber process offers faster cycle times, resulting
in lower production costs.
Due
to the low melting temperature of zinc die casting alloys, dies for zinc parts
last longer; often 3-4 times longer than the same dies when used for casting
aluminum alloys.
Permanent
Mold Casting
ZA-8
and ZA-12 are generally considered for permanent mold applications. Permanent
mold casting has traditionally been done using steel or cast iron molds, but is
now also performed in graphite molds. Permanent mold casting often competes
with sand casting by providing tighter tolerances and a smoother surface finish
which can reduce machining operations. Permanent mold casting is a
competitive alternative to die casting when lower annual volumes are required.
Ferrous
permanent molds designed for aluminum alloys are generally suitable for casting
zinc alloys. However, due to the superior casting fluidity of zinc, thinner
sections can be cast. This process is well suited for medium production runs of
500-10,000 pieces. Ferrous permanent mold casting has great flexibility in
terms of part size, ranging from ounces up to 100 lbs.
Graphite
permanent mold casting offers some distinct advantages over metal tooling.
Improved tolerances, lower tooling costs, and a superior surface finish are all
benefits of the graphite mold process. Drawbacks are limited component size,
complexity and coring.
Sand
Casting
All
the ZA alloys are suitable for sand casting; however, ZA-12 is the most
popular. Sand casting offers the greatest design flexibility in terms of size,
complexity and quantity requirements. Tooling costs are generally low; and,
therefore, facilitating low volume production. However, surface smoothness and
tolerance capabilities are limited, usually requiring machining.