Common metals used in die casting include zinc and aluminum. These are usually not pure metals; rather are alloys which have better physical characteristics.

In recent years, injection-molded plastic parts have replaced some die castings because they are usually cheaper (and lighter--important especially for automotive parts since the fuel-economy standards). Plastic parts are practical (particularly now that plating of plastics has become possible) if hardness is not required and if parts can be redesigned to have the necessary strength.

Process :------

There are four major steps in the die casting process. First, the mould is sprayed with lubricant and closed. The lubricant both helps control the temperature of the die and it also assists in the removal of the casting. Molten metal is then injected into the die under high pressure. The high pressure assures a casting as precise and as smooth as the mold. Typically it is around 100 MPa (1000 bar). Once the cavity is filled then the pressure is maintained until the casting has become solid (though this period is usually made short as possible by water cooling the mold). Finally, the die is opened and the casting is ejected.

Equally important as high-pressure injection is high-speed injection--required so the entire cavity fills before any part of the casting solidifies. In this way, discontinuities (spoiling the finish and even weakening the casting) are avoided even if the design requires difficult-to-fill very thin sections.

Before the cycle can be started the die must be installed in the die casting machine (set up) and brought to operating temperature. This set-up requires 1-2 hours after which a cycle can take anywhere between a few seconds to a few minutes depending on the size of the casting. Maximum mass limits for magnesium, zinc, and aluminium parts are roughly 4.5 kg, 18 kg, and 45 kg, respectively. A typical die set will last 500,000 shots during its lifetime with lifetime being heavily influenced by the melting temperature of the metal or alloy being used. Aluminum and its alloys typically shorten die life due to the high temperature of the liquid metal resulting in deterioration of the steel mold cavities. Molds for die casting zinc last almost indefinitely due to the lower temperature of the zinc. Molds for die casting brass are the shortest-lived of all. This is despite, in all cases, making the mold cavities out of the finest "hot work" alloy steel available.

A shot occurs every time the die is filled with metal. Shots are different from castings because there can be multiple cavities in a die, yielding multiple castings per shot. Also the shot consists not only of the individual castings but also the "scrap" (which, unlike in the case of scrap from machining, is not sold cheaply; it is remelted) that consists of the metal that has hardened in the channels leading into and out of the cavities. This includes, for example, the sprue, runners and overflows. Also there is usually some unplanned-for thin scrap called flash, the result of molds.