Extrusion Process Basics
For those new to the aluminum extrusion process, the example below is a fun way to show how the process works. The extrusion process is similar to this PlayDoh® press in that the malleable dough is forced through the press and flows through the opening fitted with a particular die shape.
For a hollow die shape, note how the PlayDoh can flow through the opening between the part of the die that forms the outside diameter and the inside “mandrel” supported by two horizontal supports. The PlayDoh SEPARATES into two tube halves and “welds” back together due to the pressure needed to make it flow through the annular opening into a tube shape.
Of course, the actual aluminum extrusion process is more complicated than this. However, with the aid of a powerful hydraulic press producing an incredible variety of useful products with almost any shape imaginable is possible with aluminum extrusion.
In the aluminum extrusion process, billet is the starting stock for the extrusion operation. Extrusion billet may be a solid or hollow form, commonly cylindrical, and is the length charged into the extrusion press container. It is usually a cast product. Often it is cut from a longer length of alloyed aluminum, known as a log.
Billet size will vary based on a number of factors, including the requirements of the extrusion press. Lengths may run from about 26 inches (660 mm) up to 72 inches (1,830 mm), and the outside diameter may range from 3 inches (76 mm) to 33 inches (838 mm); 7-inch (178 mm) to 10-inch (254 mm) diameters are the most common.
Direct Extrusion Operation
| This diagram shows the basic steps involved in extruding an aluminum profile.
Once the desired shape for the finished profile has been developed and the appropriate aluminum alloy selected, an extrusion die, and associated tooling, is produced. In the actual extrusion process, the aluminum billet (a cast "log" of extrusion feedstock) and extrusion tools are preheated. During extrusion, the billet is still solid, but has been softened in a furnace. Note: The melting point of aluminum is approximately 1,220° Fahrenheit (660° Centigrade). Extrusion operations typically take place with billet heated to temperatures in excess of 700°F (375°C), and — depending upon the alloy being extruded — as high as 930°F (500°C).
The actual extrusion process begins when the press ram starts applying pressure to the billet within a container. Hydraulic presses can exert from 100 tons to 15,000 tons of pressure; the pressure capacity of a specific press determines 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.
These photos show a new length of extrudate just emerging from the
press (left) and the production of a profile in progress (right).
The formed profile is cut off at the die and the remainder of the metal is removed to be recycled. After it leaves the die, the still-hot extrusion may be quenched, mechanically treated, 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 anodized), fabricated (cut, machined, bent, welded, assembled), or packed for shipment.