Technical
Information and Advice
Article Three
Benefits of diecasting in Zinc
Accurate and Consistent Tolerances
Diecasting can produce castings with accuracy comparable
to machining tolerances. Typical precision of 0.025mm
in 25mm is possible - i.e. 0.1% of the dimension. Equally,
once tolerances have been achieved, they are set for
life, giving long term production consistency. This
has tremendous benefits for automated assembly processes
where consistent accuracy is vital.
Eliminating Machining
The precision of the diecasting process allows accurate
and intricate detail to be cast to size, eliminating
machining completely. Internal threads and undercuts
are however readily machined.
Thin Wall Capability
All the zinc alloys have excellent castability, so thin
walled cross-sections are possible. Zinc components
are often cast to a thickness of 1.O mm, with thinner
sections possible on occasions. Thin wall castings have
a superior strength to weight ratio, through a dense
skin forming on the casting with a superior grain structure.
Thus strong and light components can be designed using
the minimum metal. Thin walls give the further benefit
of increased production rates due to faster solidification
in the die.
Zero Draft Angle Castability
Draft angle is the taper on the surface of a die required
to facilitate ejection of the cast part from the die
cavity. In general zinc alloys can be diecast with less
draft angle than competitive materials, and in some
cases can be cast with parallel cored holes and outer
walls, i.e. zero draft angle.
Long Tooling Life
As zinc alloys are much less aggressive to dies than
the higher melting point, lower ductility alloys, the
dies for zinc parts often last for around 1 million
shots, a ratio of typically six times longer than the
equivalent casting process for aluminium.
Volumes
Pressure diecasting is most appropriate to high volume
precision castings, and accounts for the vast majority
of zinc alloy castings produced. Diecasting is typically
economic for volumes of 20,000 up to millions per year,
though for high value added products, lower volumes
may prove worthwhile.
Production Rates
The traditional zinc alloys plus ZA 8 and ACuZinc®
can be run in "hot chamber" diecasting machines. These
run at a much faster cycle time than the "cold chamber"
machines which aluminium alloys use. Hot chamber machine
production rates vary from 200-500 shots per hour for
larger components, to 400-2000 shots per hour for smaller
components, dependent on the type and configuration
of the machine. In many cases it is also appropriate
to have multiple cavities within the die, further increasing
the production rate. |
