Extrusion is the process of shaping a piece of solid material, such as aluminum, by forcing it through a smaller opening. A large press is used to force the material through a shaped hole called a die. Extrusion produces many shapes, including bars, tubes, and wires. Metals, plastics, and rubber can be extruded.
The direct process (also called forward process) is the most widely used method of extrusion. In this process, a ram (plunger) pushes against a billet (short piece of metal or plastic) from one end of an enclosed chamber. The ram forces metal or plastic material through a die opening at the other end of the chamber. Such great force is used that the material flows out like toothpaste out of a tube.
Aluminum beverage cans are made with a specialized extrusion process known as impact extrusion. In impact extrusion, the material is forced into a hollow cylinder or tube shape.
Extrusion for metals can be done with either room temperature or heated material. The hot extrusion process is used most often because heat improves the material’s ability to be shaped. Heat also reduces the force required for shaping. Before extrusion, metal billets can be heated to temperatures ranging from 400 °F (204 °C) to more than 2000 °F (1093 °C), depending on the type of metal that is extruded.
During plastic extrusion, plastic pellets are heated and mixed with additives in a chamber called an extruder. The soft plastic mass is forced through the extrusion die and cooled as it exits. Extruding plastics can produce such shapes as pipe for homes and fine threads for clothing.
