Die Casting – design guide, materials, advantages and disadvantages

September 12, 2018
EngineeringClicks

There are two main types of die casting, pressure die casting and gravity die casting
Pressure die casting involves the injecting of molten metal into a custom mould where the chamber can be preheated or cold
Gravity die casting involves the pouring of molten metal into a preheated custom mould using gravity

Pressure Die Casting PDC process diagram — PDC process diagram. Image is © 2018 EngineeringClicks

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

Gravity Die Casting (GDC) process diagram — GDC process diagram. Image is © 2018 EngineeringClicks

Applications

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?

Both types of Die Casting are used for the processing of non-ferrous metals including magnesium, copper and aluminum. Additional metals like nickel, iron and lead can be used for GDC.

Design Considerations

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.

Die Casting materials - LM6 ingots — Ingots of LM6 aluminium alloy ready to be Die Cast

Process Variations

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.

Economic Considerations

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.

Die casting - an automotive part — A Die Cast automotive part featuring post-machined surfaces

Quality Considerations

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.