Introduction of Die Casting (Hot Working Technology)

Casting is one of the oldest metal working techniques known to man. Our country made metal castings as early as 2000 B.C., and the process used then is not much different in principle from the one used today.

Foundry processes consist of making molds, preparing and melting the metal, pouring the metal into the molds, and cleaning the castings. The product of the foundry is casting, which may vary from a fraction of a kilogram to several hundred tons. It may also vary in composition as practically all metals and alloys can be cast.

The metals most frequently cast are iron, steel, aluminum and so on. Of these, iron, because of its low melting point, low price and ease of control, is outstanding for its suitability for casting and is used far more than all the others.

Casting is a widely used method of producing metal products, particularly those which are intricate. Since molten materials will readily take the shape of the container into which they are poured, it nearly as easy to cast fairly complex shapes as to produce simple forms.
The place where the metals are cast is called a foundry. The most important of cast metals is cast iron , which is made from pig iron by remelting it in a special melting furnace, called a cupola.

From the cupola, the cast iron flows into ladles of different size, and from these ladles it is poured into the molds.

The molds may be of two kinds: sand molds and metal molds. A metal mold consists of two hollow parts, which should be joined for pouring the metal into it. The inside of this mold is covered with carbon or graphite so that the metal could not stick to the wall of the form. When the metal has solidified, these hollow parts are disjoined and the casting is taken out. These are also special molds in which large blocks of steel can be cast. These molds are usually made of cast iron and are called ingot molds, which the blocks of steel produced by pouring the metal into these molds are called ingots and the process is called ingot casting.

    
A relatively wide range of nonferrous alloys can be die-cast. The principal base metals used, in order of commercial importance, are zinc, aluminium, copper, magnesium, lead, and tin. The alloys may be further classified as low-temprature alloys and high-temperature alloys; those having a casting temperature below 538°C , such as zinc, tin, and lead, are in the temperature class. The low temperature alloys have the advantages of lower cost of production and lower die-maintenance costs. As the casting temperature increases, alloy and other special steels in the best treated condition are required to resist the erosion and heat checking of die surfaces. The destructive effect of high temperatures on the dies has been the principal factor in retarding the development of high-temperature diecastings.

Another factor governing the choice of alloy is the erosive or solvent action of the molten metal on the respective machine parts and dies. This action increases with temperature, although it is more pronounced with some alloys than with others. Aluminium, in particular, has a destructive action on ferrous metals and, for this reason, is seldom melted in the machine, whereas the copper-base alloys are never melted in the machine.