The aluminium extrusion process is similar to squeezing toothpaste out of a tube or forcing icing out of an icing bag to decorate a cake. Pressure is applied at one end forcing the paste out through a shaped nozzle. Bakers use a variety of nozzles producing a variety of shapes. Similarly you can squeeze aluminum through a shaped opening, with the aid of a powerful hydraulic press, producing an incredible variety of useful products with almost any shape imaginable.
In the actual extrusion process the aluminum billet (a cast “log” of extrusion ) and the extrusion die are preheated. During extrusion, the billet is still solid, but has been softened in a furnace by being heated to a typical temperature of 350°C. (The melting point of aluminium is 660°).
The extrusion process begins when the heated billet is put into a container and a ram forces the billet against the back of the die. Presses can exert from 100 tons to 15,000 tons of pressure; the pressure capacity of a press will determine how large an extrusion it can produce.
As pressure is applied, the billet is first crushed against the die, becoming shorter and wider until its expansion is restricted by the container walls. Then, as the pressure increases, the soft (but still solid) aluminum has no place else to go and begins to squeeze out through the shaped die to emerge on the other side as a fully formed profile.
The extruded profile is cut off at the die. After it leaves the die, the still-hot extrusion may be cooled by either air or water, and aged to impart desired metallurgical properties and physical performance.
After sufficient aging, whether in an aging oven or at room temperature, the profiles are moved to other areas of the plant and may be finished (painted or anodised), fabricated (cut, machined, bent, welded, assembled), or packed for shipment.
With thanks to The Aluminum Extruders Council