Die casting is a metal casting process that pushes molten metal under high pressure into a hollow cavity which sets the shape of the metal as it cools. The molds themselves are typically constructed from non-ferrous metals such as zinc, copper, aluminum, magnesium, lead, pewter, or tin-based alloys.
Due to the higher cost of the actual casting equipment and metal dies, die casting tends to serve high-volume production demands. Nonetheless, once set into production, the process of manufacturing parts using the die casting method is a relatively simple and low-cost process. Some of the other benefits of die casting include excellent surface finishes and dimensional consistency.
The process of die casting traditionally involves 4 steps: the preparation of the die, filling, ejection, and shakeout. In preparation, each die is lined with a lubricant that helps both control the temperature and assists in the ultimate removal of the casting itself. In filling, two die halves (consisting of the cover and ejector half) are closed together and molten metal is injected into the cavity at high pressure. Once the mold is filled, the pressure is maintained until the casting solidifies, whereupon the die is opened and ejected from the cavity. In the final step, the scrap which includes ancillary and flash materials, are separated and recycled.
In general there are two types of die casting machines: hot-chamber and cold-chamber machines.
Hot Chamber Die Casting
In hot-chamber die casting systems, molten metal is forced by a piston into the dies. The advantages of this type of die casting process include radio cycle times and the convenience that comes with melting the metal in the casting machine itself. The disadvantages include its limitation of use with only low-melting point metals and that aluminum cannot be used since it readily combines with iron whilst in a molten pool. As such, hot-chamber machines are predominately utilized for metals such ads zinc, tin, and lead comprised alloys.
Cold Chamber or Aluminum Die Casting
Metals that cannot be used in the hot chamber method, such as aluminum and zinc alloys, are used in cold-chamber die casting. This process begins by melting the metals in a separate furnace rather than in the casting machine itself. An amount of molten metal is then removed and fed into an injection cylinder, which is then extruded into the die by a piston. Because of the additional step required in transferring the metal to the injection cylinder, the cycle-times associated with cold chamber casting may be considerably slower. Overall, die casting has a number of advantages which include:
- Smooth Surface Finishes
- Inclusion of inserts
- Elimination of some secondary machining process
- Rapid production
- High strength and dimensional accuracy