Die casting is a metal casting process that is characterized by forcing molten metal under high pressure, in general aluminium or zinc, into a mould cavity. This particular process was introduced in the US during the second half of the 19th century.
The mould used for die casting process is composed of two hardened steel half-dies, so that only metals with a melting point lower than the melting point of the material the die is made of can be cast.
The metals that are used in the die casting process are mostly aluminium and zinc alloys. The pressure which is necessary to inject the metal is in general very high and can go from 20 to 1500 bars. The cooling of the die is made through a cooling liquid circulating inside a cooling system.
This system allows also the cooling of the casting inside the mould; once the die casting has solidified and cooled, it is ejected from the die halves.
The die casting process in our foundry is fully automated and can therefore allow a high productivity.
Thanks to the die casting process the die castings have extremely close tolerances and a surface finishing better than the one obtained with the traditional casting processes (sand casting and shell-mould casting).
Die casting process can be distinguished in:
hot-chamber die casting and cold chamber die casting.
In the hot-chamber die casting the injection mechanism is immersed in the molten metal bath of a metal holding furnace. It allows a better control of the casting temperature and a higher productivity, as the molten metal is taken directly from the tank. The pressure needed for hot-chamber die casting is lower than the one needed for cold-chamber die casting and it does not usually exceed 130/140 bars.
Hot-chamber die casting is usually employed for zinc alloys (zamak) and allows a high-quality surface finish.
In the cold-chamber die casting the control of the casting temperature and the productivity are lower than in the hot-chamber die casting, as the injection of the molten metal in the mould takes longer. Cold-chamber die casting allows more flexibility in the choice of the casting alloy. The pressure needed for cold-chamber die casting is generally higher than the one needed for hot-chamber die casting and it can reach up to 1500 bars.
Cold-chamber die casting is usually employed for aluminium alloys. It is used for zinc alloys when high mechanical properties of the die castings are required; the level of the surface finishing of zinc die castings obtained with cold-chamber process is lower than the surface finishing obtained with hot-chamber die casting.