Gravity Die Casting
Sometimes referred to as permanent mould, Gravity Die Casting (GDC) is a repeatable casting process used for non-ferrous alloy parts, typically aluminium, zinc and copper based alloys. The process differs from high pressure die casting (HPDC) in that gravity – rather than high pressure – is used to fill the mould with the liquid alloy.
GDC is suited to medium to high volumes products and typically parts are made of heavier sections than HPDC, but thinner sections than sand casting.
There are three key stages in the process:
- The heated mould is coated with a die release agent. The release agent spray also has a secondary function in that it aids cooling of the mould face after the previous part has been removed from the die.
- Molten alloy is poured into channels of the tool to allow the material to fill all the extremities of the mould cavity. The alloy is either hand poured using steel ladles or dosed using mechanical methods. Typically, there is a mould “down sprue” that allows the alloy to enter the mould cavity from the lower part of the die, reducing the formation of turbulence and subsequent porosity and inclusions in the finished part.
- Once the part has cooled sufficiently, the die is opened, either manually or utilising mechanical methods.
Advantages of GDC
- Good dimensional accuracy
- Smoother cast surface finish than sand casting
- Improved mechanical properties compared to sand casting
- Thinner walls can be cast compared to sand casting
- Reverse draft internal pockets and forms can be cast in using preformed sand core inserts
- Steel pins and inserts can be cast into the part
- Faster production times compared to other processes.
- Once the tooling is proven, the product quality is very repeatable.
- Outsourced tooling setup costs can be lower than with UK sand casting.
