Know About the Techniques Used in Aluminium Die Casting

Aluminium casting processes are generally classified as Ingot casting or Mould casting. In the first process, primary or secondary aluminium is casted into wire bar ingot, rolling ingot (slab) and extrusion ingot (billet).All these are subsequently transformed in semi- and finished products.

For producing cast products the second process is used in the foundries. In manufacturing shaped components this is the oldest and simplest means.

In aluminium casting, die casting is a common method. Few other techniques such as \"lost foam\" or \"wax pattern\" processes are also used but compared to the both listed techniques their economic importance is considerably lower.

Low Pressure Die Casting

For the production of components that are symmetric about an axis of rotation, low-pressure die casting is especially suited. By this technique light automotive wheels are normally manufactured.

Die Casting

At each cast, the mould is not destroyed in this method but it is permanent as it is made of a metal such as cast steel or iron. You will find a number of die casting processes. The most widely used one is the high pressure die casting, representing about 50% of all light alloys casting production.

The use of low pressure die casting is increasing and currently accounts for about 20% of production. For the rest of the part, Gravity die casting accounts along with the exception of a growing but small contribution from the recently introduced vacuum and squeeze die casting process.

High Pressure Die Casting

In this process, at high speed and high pressure the liquid metal is injected into a metal mould.

This equipment generally consists of two vertical platens on which bolsters are located which hold the die halves. In order the die can be opened and closed, one platen is fixed and the other can move. Into the shot sleeve a measured amount of metal is poured and using a hydraulically-driven piston it is introduced into the mould cavity. The die is opened once the metal has solidified and the casting removed.

Special precautions must be taken during the process to avoid too many gas inclusions which during subsequent heat-treatment or welding of the casting product can cause blistering. Both the machine and its dies are very expensive, and due to this reason pressure die casting is economical and that to for high-volume production.

Vacuum Die Casting

In this case the principle is the same as low-pressure die casting. With the help of a vacuum pump the pressure inside the die is decreased and due the difference of pressure forces the liquid metal is forced to enter the die. Compared to other casting techniques this transfer is less turbulent so that gas inclusions can be very limited. Consequently, this new technique is specially aimed for the components which can subsequently be heat-treated.

Gravity Casting

The Cores (inner parts of the mould) in gravity casting are usually made of bonded sand. For mass production and for fully mechanised casting, gravity die casting is suitable.