What is Gravity Die Casting?
Gravity Die Casting is a permanent mould casting process, where the molten metal is poured from a vessel or ladle into the mould.
The mould cavity fills with no force other than gravity, filling can be controlled by tilting the die. Undercuts, and cavities can be incorporated into the component form with the use of sand cores. This process gives a better surface finish than sand casting as well as better mechanical properties, both due to rapid solidification.
Permanent mold casting is typically used for high-volume production of small, simple metal parts with uniform wall thickness. Non-ferrous metals are typically used in this process, such as zinc alloys, aluminum alloys, magnesium and copper alloys (brass alloys). However, irons and steel alloys can also be cast in this method using graphite molds.
Compared to sand casting, this process requires less finishing and fettling and gravity die casting tends to produce a higher quality product. The Gravity die casting production method is generally less cost effective in the manufacture of tooling compared with sand casting.
Gravity Die Casting Process
The gravity casting process consists of the following steps:
1. Mold preparation
First, the mold is preheated to around 300-500°F (150-260°C) to allow better metal flow and reduce defects. Then, a release agent (refractory material or ceramic coating) is applied to the mold cavity surfaces to facilitate part removal and increase the mold life.
2. Mold assembly
The mold consists of at least two parts – the two mold halves and any cores used to form complex features. Such cores are typically made of iron or steel, but expendable sand cores are sometimes used. In this step, the cores are inserted and the mold halves are clamped together.
3. Pouring
The molten metal is poured at a slow rate from a ladle into the mold through a sprue at the top of the mold. The metal flows through a runner system and enters the mold cavity.
4. Cooling
The molten metal is allowed to cool and solidify in the mold.
5. Mold opening
After the metal has solidified, the two mold halves are opened and the casting is removed.
Trimming – During cooling, the metal in the runner system and sprue solidify attached to the casting, is cut off and this excess material is now removed.
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What can be made with Gravity casting?
- Gears
- Splines
- Gear Housings
- Pipe Fittings
- Wheels
- Valve and pump parts
etc
What is difference between Gravity casting and sand casting?
There are a wide range of key differences regarding gravity casting and sand casting. The main differences lie in the mold and how it is structured. Sand casting is accomplished by shaping a mold from a sand mixture and pouring molten liquid metal into the cavity in the mold. The mold is then cooled until the metal has solidified. It is essentially an expendable mold casting process since the mold is destroyed after its initial use. Additionally, sand casting allows for smaller batches to be made compared to permanent mold casting, which is designed for larger runs and is costlier.
Conversely, gravity casts can be used repeatedly to make identical parts. This type of reusable mold casting is highly useful for applications that require numerous production runs of the same part. The initial investment costs are a bit higher than sand casts, but the costs generally make up for themselves due to the extended usage factor.
More Gravity casting products
