Die casting is a permanent mould casting process in which molten metal is poured into a mould and removed after solidification. There are two main types of this process: Gravity Die Casting (GDC) and Pressure Die Casting (PDC). In GDC, molten metal is poured into the mould using gravity. In PDC, the molten metal in injected into the mould under pressure. PDC is further divided into two types: Cold Chamber Die Casting and Hot Chamber Die Casting. Following are some of the general steps performed in Die Casting:
1. Raw metal is melted so it can be poured or injected into the mould cavity.
2. Except for Cold Chamber Die Casting, moulds are heated before introducing the molten metal.
3. The moulds are closed and molten metal is poured or injected into the mould.
4. The moulds are left closed until the molten metal solidifies.
5. The moulds are opened and the cast part is removed
- GDC is used for the production of engine components like pistons, connecting rods, gears, cylinder heads and other components.
- PDC is used for the production of pump components like pump casing impeller parts, machine parts and engine parts.
What materials can be Die Cast?
- In GDC geometry complexity is limited, whereas in PDC highly complex geometries can be produced.
- PDC (0.8 to 2.5 mm) requires more tolerance than GDC (0.8 to 1.5mm).
- In GDC the parting line is normally vertical whereas in PDC it depends on the geometry and critical dimensions.
- PDC is also divided into high and low pressure Die Casting.
- Pressure range on the Hot Chamber Die Casting is from 7 to 35 MPa.
- Pressure range for Cold Chamber Die Casting is from 14 to 140 MPa.
- Cores can be used for internal cavities and hollow parts.
- GDC has a lower production rate (typically a few pieces per hour) compared to PDC, which can produce a few hundred parts per hour.
- In GDC, a typical lead time is in weeks and in PDC it may be in months due to the complexity of the die required for the process.
- Costs related to tooling, labor, equipment and finishing, range from low to moderate in GDC and very high in PDC.
- Porosity is rarely an issue with GDC, but can be a big problem with thick and long parts produced by PDC.
- Mechanical properties are fair in GDC but poor in PDC.
Advantages and Disadvantages of Die Casting
Advantages: Production rate is moderate to high. Close tolerances are possible.
Disadvantages: Poor control over mechanical properties. Extra quantity of material required during the process.