Extrusion is defined as the process of shaping material, such as aluminum, by forcing it to flow through a shaped opening in a die. Extruded material emerges as an elongated piece with the same profile as the die opening.
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 billet is inserted into the holding chamber and pressure is applied to the handle, which forces billet through the shape.
Press size determines how large of an extrusion can be produced. Extrusion size is measured by its longest cross-sectional dimension. The most important factor in the extrusion process is temperature. Temperature is most critical because it gives aluminum desired characteristics such as hardness and finish.
The steps in the extrusion process are as follows:
1. Billets must be heated to approximately 800-925 ￠X F.
2. After a billet reaches the desired temperature, it is transferred to the loader where a thin film of smut or lubricant is added to the billet and to the ram.
3. The billet is transferred to the cradle.
4. The ram applies pressure to the dummy block which, in turn, pushes the billet until it is inside the container.
5. Under pressure the billet is crushed against the die, becoming shorter and wider until it has full contact with the container walls. While the aluminum is pushed through the die, liquid nitrogen flows around some sections of the die to cool it. This increases the life of the die and creates an inert atmosphere which keeps oxides from forming on the shape being extruded.
6. As a result of the pressure added to the billet, the soft but solid metal begins to squeeze through the die opening.
As an extrusion exits the press, the temperature is taken with a True Temperature Technology (3T) instrument mounted on the press platen. The 3T records exit temperature of the aluminum extrusion. The main purpose of knowing the temperature is to maintain maximum press speeds. The target exit temperature for an extrusion is dependent upon the alloy. For example, the target exit temperature for the alloys 6063, 6463, 6063A, and 6101 is 930￠X F (minimum).
7.Extrusions are pushed out of the die to the leadout table and the puller, which guides metal down the run-out table during extrusion. While being pulled, the extrusion is cooled by a series of fans along the entire length of the run-out and cooling table.
8. When the extrusion reaches a desired length, the extrusion is cut with a profile saw or a shear.
10.Metal is transferred (via belt or walking beams systems) from the run-out table to the cooling table.
11. After the aluminum has cooled and moved along the cooling table, it is then moved to the stretcher. Stretching straightens the extrusions and performs ‘work hardening’ (molecular re-alignment which gives aluminum increased hardness and improved strength).
12.The next step is sawing. After extrusions have been stretched they are transferred to a saw table and cut to specific lengths.