Aluminum extrusion is a process in which aluminum billet is pushed through a steel die to produce a part that has a uniform cross-section. The extrusion process can produce aluminum extrusions that have a very complex cross section. The process begins with the billet which is the aluminum alloy that is heated to 700 degrees Fahrenheit for soft alloy or 930 degrees Fahrenheit for hard alloy. Since the melting point of aluminum is 1220 degrees Fahrenheit, the billet is still a solid but has been softened by high temperature.
The most common type of aluminum extrusion is direct extrusion in which the heated billet is forced through a stationary die by a dummy block that is driven by a hydraulic ram. In indirect extrusion, the die is contained within a hollow ram. The ram and die move through the stationary billet forcing the aluminum into the ram as the aluminum takes the shape of the die.
Aluminum extruders use powerful hydraulic pressures which vary from 100 to 15,000 tons. The rate at which an aluminum extrusion can be produced depends on the exact composition of the aluminum alloy. For a soft alloy, aluminum extruders can produce extrusions at the rate of 180 feet per minute if the cross section is a simple shape. For harder alloy and more complex cross sections, the rate can be as slow two feet per minute.
The aluminum extruder is capable of producing continuous sections as long as 200 feet on each pass. The extrusion is cooled either naturally or using air/water cooling. After the cooling process, the extrusion is loaded onto buggies and placed into ovens for the final phase. In this phase, the temperature is brought to approximately 400 degrees and heat treated for 8-10 hours. This heat treating process is what gives the aluminum it’s full hardness properties.