Extrusion refers to the process of creating a particular shape in a material such as aluminum, through pressing it through an opening inside a die. The extruded material is an elongated part that shares the same shape as its opening in the die.
To better understand the process of extrusion using aluminum, think about a Play-Doh(r) Fun Factory and how it operates. The Fun Factory is the extrusion press. The handle serves as the ram and the shape bar acts as the die. Play-Doh(r) is on the other hand, is an aluminum billet. The first step is to choose the desired shape and color. The shape is the die, and the color the alloy or temper. The Play-Doh (r) is then inserted into the container holding it. Pressure is applied to handle, which is used to push PlayDoh(r) into the design. In an extrusion press pressure is applied to the block by the ram, where the dummy block is attached to the end of the ram stem. It is “extruded” when Play-Doh(r), appears. Extrusions made from aluminum billets adhere to the same principles, but Tamilnadu Aluminium Company employs more advanced technology.
Press size determines the size of an extrusion is made. The largest dimension of an extrusion is its cross-sectional length, i.e. It must fit within a circumscribed circle. The circumscribed circle is the smallest circle that will completely enclose the cross-section of an extruded form.
The most important thing to remember in the process of extrusion is temperature. Temperature is most critical as it allows aluminum to acquire desired characteristics , such as the hardness and finish.
STEPS OF THE ALUMINUM EXTRUSION PROCESS
- Billets must be heated to around 800-925 deg F.
- Once a billet has reached the desired temperature it is transferred to the loader. There, a thin layer of smut (lubricant) is applied to the billet and the ram. The smut serves as a lubricant which acts as a separation agent that prevents the pieces from sticking together.
- The billet then moved to the cradle.
- The ram exerts pressure on the dummy block which, it pushes back the billet until it’s inside the container.
- Under pressure the billet is crushed against the die, becoming shorter and wider until it has full contact with the walls of the container. When the aluminum is being pushed through the die, nitrogen liquid flows over a portion of the die to cool it. This reduces the die’s life and protects the shape of the extruded from forming oxides. In some cases, nitrogen gas may be substituted for liquid nitrogen. Nitrogen gas does not cool the die but does provide an inert atmosphere.
- The billet is compressed with an increase in pressure and then the solid, soft metal begins to squeeze through the opening of the die.
- The temperature of the extrusion at the time it exits the press can be measured with True Temperature Technology (3T) which is mounted on the platen. The 3T is a device that records the temperature at the exit of the aluminum extrusion. The main purpose of knowing the temperature is to keep maximum speeds for the press. The alloy determines the extrusion’s departure temperature. The temperature that is ideal for exiting for 6063A, 6463A, 6063A, and 6101 is 930deg F (minimum). 6061 and 6005A are, respectively, 95 and 930 degrees F.
- Extrusions are pulled out of the die before being pushed towards the leadout tables as well as the puller. This is used to guide the metal through the run-out while extruding. When pulled, the extrusion gets cooled by an array of fans running along all the length of the run-out and cooling table. Be aware that Alloy 6061 can be quanned with air or water.
- You aren’t able to use all of the billet. The butt (remainder) is comprised of oxides derived from the skin of the billet. The butt is then sheared off and discarded . Meanwhile, a different billet is loaded, then welded to a previously loaded billet and extrusion continues.
- When the extrusion is at the length desired the extrusion can be cut with a profile saw or a shear.
- Metal is transferred by belt or walking beams from the run-outs to the cooling tables.
- After the aluminum has cooled and moved to the cooling table it is then moved into the stretcher. The extrusions are straightened and work hardening (molecular alignment) is done. This gives aluminum increased hardness and strength. Find the manufacturers of aluminum profiles.
- The next step is sawing. After extrusions have stretched they are transferred to a saw table and cut to the required lengths. The cutting tolerance of saws is 1/8 inch or greater according to the length of the saw.
After the pieces have been cut, they are placed onto a transporter and placed into ovens for ageing. The process of heat treating, also known as artificial aging, accelerates the aging process by reducing the temperature over an exact period of time.