“Extrusion” is often defined as the process of shaping a material, such as aluminum, by forcing it to flow through a shaped opening in a die. The extruded material emerges as an elongated piece with the same profile as the die opening. In thinking about the extrusion process, consider a Play Doh Fun Factory and how it might work. Think of the Fun Factory as the extrusion press, the handle as the ram, the shape bar as the die, and the Play Doh as the aluminum billet.
The first step is to choose the desired shape and color. Think of the shape as the die which will be used and the color as the temper and alloy needed. Next, the Play Doh is inserted into the holding chamber and pressure is applied to the handle, which forces Play Doh through the shape. In an extrusion press, pressure is applied to the billet by the ram where the dummy block is attached to the end of the ram stem.
When Play Doh begins to emerge, it has effectively been “extruded”. The same principles apply to extrusions from aluminum billets but considerably more detailed and sophisticated technology are involved. Press size determines how large of an extrusion can be produced. Extrusion size is measured by its longest cross-sectional dimension (i.e. its fit within a circumscribing circle). A circumscribed circle is the smallest circle that will completely enclose the cross section of an extruded shape. The most important factor to remember in the extrusion process is temperature. Temperature is most critical because it gives aluminum desired characteristics such as hardness and finish.