The gravity die casting

Technical publication
The gravity die casting
Innovative Solutions
Copyright © 2013 Saint Jean Industries Certification Systèmes Qualité ISO 9001, ISO/TS 16949 & ISO 14001
Technical publication
The gravity die casting process in
permanent mold
This molding technique is widely used for the manufacture of castings parts made of non-ferrous alloys
such as aluminum, magnesium, copper or zinc. This
is mainly due to the low melting temperatures not
exceeding 1000°C. For this type of casting, metal is
poured at atmospheric pressure in a “permanent»
mold, made from two machined steel blocks. Cavity, which will form the final part, is machined from
solid block. Each block represents an half of the final workpiece: the upper mold and the lower mold
connected by a parting line determined during the
design phase. The parting line position is essential
to remove the part without damaging the mold or the
piece after the solidification phase.
The gravity casting can produce complex parts, sometimes with cavity or pin hole thanks to sand cores
or metal pins.
From medium to mass production
To reach the required production rate for high volume markets such as automotive, it is necessary to
provide grip molds, and cooling to accelerate the solidification phase. Because of the equipment price,
this method is not suitable for small series (> 250
parts). For small series we should choose between
permanent mold or sand mold casting.
Upper mold
Parting line
Mold’s basin
Lower mold
Gravity process steps
The example of tilt pouring process used by Saint
Jean Industries:
1
Before starting a series of molding, the mold
must be prepared by a step of die coating. This
prevents adhesion of the molten metal on the
mold, and control thermal behavior of the part.
Then the prepared molds are mounted for instance on rotary casting machines.
2
Technical publication
Gravity process steps
3
4
5
A holding furnace is filled with the molten alloy to
flow, and the mold’s basin is poured by a ceramic ladle.
When the ladle is empty and the mold’s basin is
full, mold switches to distribute the metal still in
the liquid phase in the mold cavity.
After switching, the mold is kept closed a predetermined period of time: this is the solidification
phase.
The two parts of the mold are opened, and the
part is removed.
6
To finish, the gates* are cut and we have a casting part.
Depending on the specifications, the part must be heat treated in order to reach the mechanical properties,
in most cases the heat treatment is a precipitation hardening of the aluminum matrix.
*The gates are some exceeding material located in the entrance of the mold. This metal suplus is at the top of the mold after the switching
operation, in this position the potential foreign matters stay at the top and are removed after.
Technical publication
Advantages of the gravity die casting in permanent mold
Some advantages of this process are:
• A very good dimensional precision thanks to high quality casting tools: the metallic mold has to be perfectly machined,
• A good surface, again thanks to the use of a permanent mold and the quality of the coating,
• High mechanical properties: effect of higher cooling rate and a shorter solidification time of the alloy,
• A smaller overall dimensions of permanent tools in comparison to the non-permanent mold casting
(sand).
Some casting samples
This process is commonly used for automotive parts such as engine bracket, torque rod, intake pipes,
cylinder heads, knuckles, brake calipers...
We use also the gravity die casting to manufacture industrial equipment, parts for power transmission that
meet sealing standards, for casings of any kind, or for cable rope hubs.
For more information about the gravity die
casting and its abilities, feel free to contact
our team directly in Saint Jean Industries:
www.st-ji.com
[email protected]