Die Casting

Advantage:
1. Excellent dimensional accuracy
2. Smooth cast surfaces Ra 1.6
3. Thinner walls can be cast as compared to sand and permanent mold casting
4. Reduces secondary machining operations.
5. Rapid production rates.

Disadvantage:

Have a small amount of porosity. This prevents any heat treating or welding, because the heat causes the gas in the pores to expand, which causes micro-cracks inside the part and exfoliation of the surface. Thus a related disadvantage of die casting is that it is only for parts in which softness is acceptable.

Definition:

A metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity.

The mold is created using two hardened tool steel dies which have been machined into shape and work similarly to an injection mold during the process.

Most die castings are made from non-ferrous metals, specifically zinc, copper, aluminum, magnesium...

Depending on the type of metal being cast, a hot- or cold-chamber machine is used.

Process:

The casting equipment and the metal dies represent large capital costs and this tends to limit the process to high volume production.

Manufacture of parts using die casting is relatively simple, involving only four main steps, which keeps the incremental cost per item low.

1. Die preparation

The dies are prepared by spraying the mold cavity with lubricant.

Lubricant both helps control the temperature of the die and it also assists in the removal of the casting.

2. Filling

The dies are then closed and molten metal is injected into the dies under high pressure: between 10 and 175 Mpa.

Once the mold cavity is filled, the pressure is maintained until the casting solidifies.

3. Ejection

The dies are then opened and the shot is ejected by the ejector pins.

4. Shakeout

Finally, the shakeout involves separating the scrap, which includes the gate, runners, sprues and flash.

Often done using a special trim die in a power press. Other methods of shaking out include sawing and grinding.