Aluminum Extrusion Process Basics
The aluminum extrusion process can be visualized using a PlayDoh® press. The process begins when the malleable dough is forced through the press and flows through the opening fitted with a particular die shape.
Hollow Die Shape
For a hollow die shape, 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, and requires a powerful hydraulic press . However, once the aluminum extruder is setup with dies and ancillary equipment, producing almost any shape imaginable is possible with suitable extrusion dies.
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.
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 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 nowhere 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.
ALUMINUM EXTRUSION MANUAL
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