There are following steps in the extrusion process.
Billets are first heated to a temperature of approximately 800-925 ° F.
It is then transferred to a loader where a very thin film of smut (lubricant) is added to the billet and also to the ram. The role of the smut is like a parting agent (lubricant) that holds back the two parts from sticking together.
The billet is then transferred to a cradle.
A ram is made to apply pressure to the dummy block that in turn, pushes the billet till it is inside the container.
The billet under pressure is crushed against the die, thus becoming wider and shorter until there is a complete contact with the container walls. As the aluminum is pushed via the die, liquid nitrogen starts flowing around few sections of the die for cooling it. This considerably increases the life of die. It creates an inert atmosphere that keeps away forming of the oxides on the shape that is being extruded. In specific cases nitrogen gas is used instead of liquid nitrogen. Nitrogen gas though does not cools the die but is able to create an inert atmosphere.
When pressure is added to the billet, the solid but soft metal starts to squeeze via the die opening.
As the extrusion leaves the press, the temperature is taken with. The exit temperature of the aluminum extrusion is recorded. The primary aim of knowing the temperature is to maintain the maximum press speeds. It is the alloy that determines the target exit temperature for an extrusion. To cite an example the target exit temperature for the alloys like 6063A, 6463, 6063, and 6101 is approximately around 930° F (minimum). Whereas the target exit temperature for alloys like 6061 and 6005A, is around 950° F (minimum).
Extrusions are then pushed out of the die into a leadout table and the puller. This guides the metal down the run-out table in an on going extrusion process. As it is being pulled, the cooling of the extrusion is done by a series of fans throughout the entire length of the run-out along with the cooling table. The following image shows the flowing of aluminium through the die.
It is a fact that all the billet cannot be used. The remainder (butt) usually contains oxides from the billet skin. The butt is then sheared off and subsequently discarded. Another billet is then loaded and welded to an already loaded billet and the extrusion process goes on.
As soon as the extrusion reaches the requisite length, the extrusion is then cut of with a profile saw or a shear.
The Aluminum is transferred (usually through a belt or walking beams systems) from the run-out table to a cooling table.
After the aluminum has properly cooled down it is moved along the cooling table. Further it is moved to a stretcher. Stretching is able to straighten the extrusion and executes the work hardening process (a molecular re-alignment that gives aluminum better strength and more hardness).
The next step is the sawing process. After the extrusions have been properly stretched they are now transferred to a saw table and cut according to specific lengths. The cutting tolerance on saws is usually 1/8 inch or even greater, depending on the length of saw. Finally, after the parts are cut, they are transported into age ovens. Heat-treating or artificial aging are used to harden the metal by speeding up the aging process in a controlled temperature environment for a pre set time.