What Everybody Ought to Know About Die Casting
Die casting is a precision high volume production process, where molten metal is injected under high pressure into a die which has a cavity in the
desired shape of the component/part. When the component has solidified, which is achieved by a coolant flowing through the die sections.
The production of die casting rates can vary from just a few components to thousands of components per hour, and the most common metals used for
this process include zinc, aluminium, and magnesium alloys. However, other less frequently used metals can include brasses, copper and copper
alloys, and this is due to their higher melting temperatures. The castability of a metal is primarily related to its melting temperature, and a few other
factors which include :
Precision of part : Part complexity : Minimum draft/taper : Minimum wall thickness
Of all the alloys available, zinc is usually considered to be the most castable, closely followed by aluminium, magnesium, and finally the various copper
alloys. The type of alloy used will inhibit maximum part size, and although the final weight of the part is considered, it is material density that is weight
per unit of volume that is the final determinant; for example; the density of zinc is .24 lb. per cubic centimeter; magnesium is .066 lb. per cubic
centimeter, so for a given weight, a component cast in magnesium will be larger in size than a part cast in zinc.
Die casting machines are usually hydraulically driven and often positioned horizontally. There are two main types of die casting machines that are
commonly in use, and these are the cold camber type and the hot chamber type. The hot chamber type is used for zinc and other lower melting
temperature alloys, but is sometimes also used for magnesium. When they are in operation, a reservoir of molten metal is seated in a furnace and this
metal is injected into the die. The injection pressure is variable from 1500 psi to over 4500 psi. ( pounds per square inch )
Cold chamber machines are mainly used for other alloys due to their higher melting temperatures. The molten metal is fed into the die from an external
furnace, and both types of machine ( hot chamber and cold chamber ) will use a cylindrical pressure vessel known as an accumulator, which is
charged with nitrogen and will boost injection pressure.
Die casting machines are rated by clamping force capacity, and the clamping systems may be either pneumatic, hydraulic, mechanical or a
combination of systems.
Die construction is common for cold and hot chamber casting. The die determines the shape of the finished part, and also act as a heat sink to cool
the casting, provide a vent for trapped gases and air and contain the mechanism to eject the finished component. The die may consist of single or
multiple cavities, and this is to produce identical multiple parts.
About the Author
Anthony Pateman from RD Castings Ltd writes about Die Casting. For more information about Die Casting visit www.rdcastings.co.uk