Aluminium extrusions - The ultimate value addition of Aluminium downstream

From simple paper clips to complex pieces used in advanced technology, aluminium extrusions are created in various shapes and sizes for value added end use utilizations. The computer you are using right now contains at least one aluminium profile in the form of a heat sink. This takes advantage of aluminium’s excellent thermal conductivity, unique anodising capability and freedom of design to keep your computer’s processor cool.

Different cross sections of extrusions

Extrusion is a process used to create objects of a fixed cross-sectional profile. A special tool called a ‘die’ is used to create these extrusions by cutting or shaping the material with the help of a press. These dies are customized to create the wanted design.

The process involves the pressing of a pre-heated solid cylinder of aluminium (billet) which is forced through the die opening. The billets are heated to a temperature range of 350 – 500 degrees Celsius. Aluminium does not glow when heated yet the malleability increases manifold at that temperature. As the aluminum extrusion emerges from the die, the temperature is in the range of 510-550°C.

The extrusion press

To cool the extrusion coming out of the die, full water quench, water sprays, and cooling fans are employed. To meet the special alloy properties, the whole process is monitored for various parameters. The end product is the extrusion of the desired shape and quality. The extrusion process may also increase the strength of the material.

Cooling through water spray

The properties of the extrusion depends on several factors:

• Design of the die
• Temperature of the billet
• Speed of the extrusion process
• The operating temperature for the process
• Grade of alloy used

As a rule, an alloy's higher mechanical properties means a lower extrusion rate. Greater friction between the liner wall and the billet results in a longer time required to start the billet extruding. The extrusion ratio of a shape indicates the amount of mechanical working that will happen as the shape is extruded.

Extrusion Ratio = area of billet/area of the shape.

Extrusion being pushed out of the die

The actual extrusion begins when the billet is pushed through the die by the ram of the hydraulic press. The aluminum billet is transferred to a loader, where a lubricant is added to prevent it from sticking to the extrusion machine. There are different designs of these presses which are capable of exerting pressures ranging from 100 tons to 15,000 tons of pressure. To avoid any formation of oxides, nitrogen in liquid or gaseous form is introduced and allowed to flow through the sections of the die. This creates an inert atmosphere and increases the life of the die. The extrusion size is measured by its longest cross-sectional dimension, sometimes referred to as its fit within a circumscribing circle diameter (CCD).

After cooling the extrusion on its arrival, a ‘stretcher’ may be used to straighten it and correct any twists that may have occurred. Conveyors then feed the work to the saw for cutting and ageing. Ageing allows for natural hardening of the extrusion and is controlled heating it in a baking oven for up to 8 hours. To adjust the colour, texture, and brightness of the aluminum’s finish, aluminum anodizing or painting may be done. This is the final step before the packaging is done by the manufacturing unit.

It is nearly impossible to ignore the applications of aluminium extrusions in every aspect of construction, transportation, and technology.

• A 2,00,000 kg aluminum truss which is housing the International Space Station has been created by the Boeing Company measuring 146 feet long, 240 feet wide and 90 feet high.
• An automobile designed with 1 pound of aluminum extrusions instead of 2 pounds of steel will save 3.1 gallons of crude oil, and prevent 20 pounds of CO2 emissions over its lifetime.
• With buildings accounting for over 40 percent of global energy consumption, it's no surprise that extruded aluminum is becoming a product of choice for green builders.
• The use of aluminum extrusions in commercial buildings can contribute to LEED (Leadership in Energy and Environmental Design) points in a number of areas including Energy Efficiency, Selection of Sustainable Materials and Indoor Environmental Quality.

Cutting the cooled extrusion

Sources:

http://www.aec.org/?page=dres_extrusion

http://www.aluminum.org/industries/processing/extrusions

https://www.bonlalum.com/education/aluminum_extrusion_process.shtml