Graphite Mold Castings
Aluminum Alloy and Zinc-Aluminum Alloy (ZA-12) Permanent Mold
The graphite permanent mold casting process combines the low cost of
machinable graphite molds with a high strength aluminum alloy or zinc-aluminum
alloy (ZA-12) to provide an economical alternative to other casting processes in
annual volumes of 500-15,000 pieces per year.
The graphite molding process is rather simple. Two mold halves with cavities cut
out in each half are pressed together and molten metal is injected into the
mold under low pressure. The mold is then held together throughout the
solidification stages of the casting. The mold halves are separated, the casting
removed, and the process is repeated.
Process Benefits of Graphite Permanent Mold Castings
- Cast precision to +/- .005 which reduces secondary machining
- Cast surface finish of 125 RMS or better
- Zinc/ Aluminum ( ZA12 ) is a 1/3 stronger than aluminum.
- Bearing qualities superior to bronze
- Excellent detailing and flatness
- Tooling leads times of only 3-6 weeks
- Porosity free castings
Casting Size
For zinc/ aluminum ( ZA -12 alloy): Lengths up to 16", widths up to 12" and
combined depths to 4 inches. These dimensions are maximum limits and are not to
be combined.
Machining
ZA-12 is an easily machined material and its lubricous nature reduces tool wear.
These features, along with the process near-net shape capabilities can
demonstrate considerable cost savings over the other methods. With in-house CNC
machining capabilities, we can provide castings complete to print and light
assembly.
Tolerances
Generally +/- .005" 1st inch: +/- .005 additional inches: +/- .002" per inch
Across parting line, add: +/- .005"
Minimum Wall Thickness
Usually .100"; however, .060" is possible on small sections MINIMUM DRAFT: 2° on
surfaces perpendicular to parting line.
Graphite Permanent Mold Tooling Description
A graphite mold is machined in two halves from a graphite block, similar
to hardened tool steels used for permanent molds thus creating a vertical
parting line.
Graphite molds are filled from the bottom by low press to minimize the
turbulence of the molten metal inside the mold.
Process controllers maximize density and minimize casting porosity by
simultaneously controlling fill rates, cycle times, and temperatures. The
result is a high quality, machine-able, ZA-12 or 356 aluminum repeatable
casting.
A graphite mold has a lower coefficient of thermal expansion that allows
it to produce parts with high accuracy. The graphite permanent mold is
extremely stable and doesn't warp, twist, or check when molten metal is
poured into it. The cavity surfaces are also non-wetting, so casting release
agents, which can degrade surface finish, aren't needed.
Graphite also stores virtually indefinitely without changing shape,
rusting, oxidizing or deteriorating. Overall, these properties let
manufacturers with medium or low volumes take advantage of a process that
delivers tight tolerances, cost effectiveness and repeatability from part to
part.
 |
|
 |
| Part being removed from graphite permanent mold showing attached
runners and gates. |
|
Graphite Mold complete with time/ temp thermocouple inserted
(controls opening / closing of mold). |
|
|
|
|
 |
|
 |
A part being removed by hand
from a graphite mold. |
|
Parts made from a graphite
mold casting. |
Back to Top