
Aluminium
Extrusion can be defined as the process that shapes aluminum, by forcibly
making it to flow through a shaped opening in a die. Extruded aluminium
comes out as an elongated piece with the same profile as that of the die
opening. A typical aluminium process is described in the schematic that
follows.
It is the size of press that determines how large an extrusion can be
produced. The most important factor to remember in the extrusion process is
temperature. Temperature is a most critical factor in extrusion as it gives
aluminum the desired characteristics such as finish and hardness.
Steps in the Extrusion Process
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 Aluminium 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.
| Aluminium Extrusion Process |
Aluminium Bars
 |
Presses
 |
Machining(Elongation)
 |
Heat Treatment
 |
Machining
 |
Surface Treatment
 |
Tool
 |
Sawing
 |
Packaging
 |
|
Types of Aluminium Extrusion process
There are the following types of extrusion process associated with aluminum
they are the following: