Types of Aluminum Extrusion

Aluminum Extrusion Nomenclature

• All types of aluminum extrusion have characteristics in common. They all involve a piece of aluminum being forced through a die; this piece is referred to as a "billet." The billet is surrounded by a metal container. A ram forces the billet through the die. The die is a mold in the shape of the desired cross-section of the extruded aluminum object. The main variations between types of extrusion involve differences in the die and the ram. The container will usually heat the billet, so as to soften the aluminum before it passes through the die.

Solid-Section Extrusion

• Solid-section extrusion is the most basic form of aluminum extrusion. The die consists of a piece of metal with a two-dimensional gap in it. When the billet is forced through the die, it forms a single solid extrusion. The cross-section of the extrusion is the same as the two-dimensional gap in the die. Solid-section extrusion is also called conventional direct extrusion.

Hollow-Section Extrusion

• Hollow-section extrusion is used to produce extrusions with hollow interiors. Examples of products produced by hollow-section extrusion include aluminum pipes and tubes. Hollow-section extrusion is essentially the same as as solid-section extrusion, except that a mandrel is held in the center of the die. As the ram forces the billet through the die, it is forced around the mandrel, creating a hollow cavity within the extrusion. The mandrel is held in place in the center of the die. Mandrels require the billet to have a hole drilled through its center. Fixed mandrels are are held in place by a dummy block. The dummy block sits between the billet and the ram. The mandrel is attached to the dummy block. The mandrel runs through the hollow center of the billet. The ram pushes the dummy block, forcing the billet through the die and around the mandrel.

Billet-on-Billet Extrusion

• Billet-on-billet extrusion enables the creation of extremely long aluminum extrusions. Before one billet has been fully pushed through the die, another die is added to the container. The pressure and temperature of the extrusion process cause the two billets to weld together. This results in a single continuous extrusion that is much longer than could be achieved using a single billet.