The mold has to be broken up after each casting operation with sand casting and shell mold casting. In the process known as die casting, the mold called a die, is made of metal and is used a large number of times. It is more expensive to make than an expendable once only mold.

An intermediate technique is the use of semipermanent molds made of fireclay or gypsum plaster, from which a limited number of castings can be obtained. The most widely used die making materials are steel, cast iron and heat resisting alloys of iron. For particular purposes other materials are sometimes employed for the dies, e.g., copper, aluminum or graphite. A die can produce castings with a smooth and clean surface and high dimensional accuracy, requiring little or no final machining or other finishing treatment. The service life of a die, in terms of the number of castings that can be produced from it, depends on such factors as the thermal shock resistance of the die material, the casting material, the temperature at which it is poured, and the casting method employed

A great many details have to be taken into consideration in designing the pattern from which the die is made. Thus, in designing the pouring-gate system and risers it must be borne in mind that the walls of the mold exert a quenching action upon the molten metal so that this solidifies much more rapidly than in sand casting. In addition, the die must be provided with fine channels at the joints and with air-vent holes and thus enable the air displaced by the casting metal to escape from the interior of the die. In a sand mold the air can escape through the porous mold material.

The die must be so constructed that it will not restrain the shrinkage that occurs when the metal cools and solidifies and will allow the casting to be easily removed. Shrinkage presents particular difficulties in designing the cores which form the cavities and recesses in the casting. Normally such cores are made of steel or special alloys. Sometimes compressible sand or shell cores are used, however.

To prevent the casting metal from sticking to the die, the latter may be given an internal coating of clay, chalk or bone ash with water glass as a binder, this mixture being applied to the die by brushing, spraying, or immersion.

In the case of simple castings the metal may be poured into the open die from the top (Fig.3). Usually the die is a closed and rather complex assembly of two or more parts, however (Fig.1), Sometimes comprising a number of cores. It must be so designed that the molten metal will flow quickly, without turbulence, into all parts of the die. For the casting of metals with a low melting point it may be necessary to use a heated die (to prevent premature solidification), and for metals with a high melting point the die may have to be artificially cooled after each casting operation.

Slowly tilting the die during casting, in order to reduce turbulence and help the metal to flow smoothly, is an expedient that is employed particularly for heavy castings (Fig.2). For the production of awkwardly shaped or very thin walled castings a vacuum may be applied to facilitate the filling of the die. Slush casting is a technique used for making hollow ornamental castings: the molten metal is poured into a die, and when a solid shell of sufficient thickness has formed, the remaining liquid is poured out.

Gravity Die Casting segment is a part of GF Automotive. It incorporates three factories in two countries (Germany and Austria).

Our expertise in the materials and processes involved has made a name for us as innovators in the international vehicle industry. We provide you with a decisive edge in time and costs, with profound know-how in all things concerning designing and processing cast aluminum alloys.

This is why numerous light alloy components manufactured in sand casting or gravity die casting processes by GF Automotive are found in the vehicles made by leading car manufacturers. For Eg. Die Castings UK specialists in gravity die casting and high pressure die casting.