In each of the single-use-mold casting processes discussed earlier, a separate mold had to be created for each casting. Variations in mold consistency, mold strength, moisture content, pattern removal, and other factors contribute to dimensional and property variation from casting to casting. In addition, the need to create and then destroy a separate mold for each casting results in rather low production rates. 

The multiple-use-mold casting processes overcome many of these limitations, but they, in turn, have their own limitations. Since the molds are generally made of metal, many of the processes are restricted to casting the lower-melting-point nonferrous metals and alloys. Part size is often limited, and the dies or molds can be rather costly.

The molds are usually made of cast iron or steel, although graphite, copper, and aluminum have been used as mold materials. The process in which we use a die to make the castings is called permanent mold casting or gravity die casting since the metal enters the mold under gravity. Some time in die-casting we inject the molten metal with a high pressure. When we apply pressure in injecting the metal it is called pressure die casting process.

Classification of Multiple Use Mold Casting Processes

Multiple use mold casting process can be further classified as below:

1. Permanent mold casting.
2. Pressure Die Casting.

Although the heaviest casting in modern industry is produced by sand casting, a large number of small castings, particularly those of non-ferrous metals, is cast by means of permanent molds. The reusable mold is machined from gray cast iron, alloy cast iron, steel, bronze, graphite, or other material. The molds are usually made of segments, which are often hinged to permit rapid and accurate opening and closing.

Permanent mold casting is also referred as "Gravity Die Casting". Since metal is fed into the mold by means of gravity, no external pressure is required. The molds require repair and renewal after long periods. The permanent molds contain the mold cavity, pouring basin, sprue, runners, risers, gates, possible core supports, alignment pins, and some form of ejection system.

Before pouring molten metal the mold is preheated and a refractory or mold coating is applied to the preheated mold, and the mold is closed and clamped tightly by means of hydraulic or pneumatic arrangement. Molten metal is then poured into the pouring basin, and it flows through the feeding system into the mold cavity by simple gravity flow. After solidification, the mold is opened and the product is removed. Since the heat from the previous cast is usually sufficient to maintain mold temperature, the process can be immediately repeated, with a single refractory coating serving for several pouring cycles. Aluminum, magnesium, zinc, lead, and copper based alloys are the metals most frequently cast, along with gray cast iron. If graphite is used as the mold material, iron and steel castings can also be produced.

Pressure die casting is a quick, reliable and cost-effective manufacturing process for the production of high volume, metal components that are net-shaped have tight tolerances. Basically, the pressure die casting process consists of injecting the molten metal into a mold cavity under high pressure and held under high pressure during solidification. Because of the combination of metal molds or dies and high pressure, fine sections and excellent detail can be achieved, together with long mold life. Most die castings are made from non-ferrous metals, specifically zinc, copper, aluminum, magnesium, lead, pewter and tin-based alloys. Ferrous-metal die castings are possible but are generally considered to be uncommon.

Die temperatures are usually maintained at about 150° to 250°C below the solidus temperature of the metal being cast in order to promote rapid freezing. Since cast iron cannot withstand the high casting pressures, die-casting dies are usually made from hardened hot-work tool steels and are typically quite expensive.