Aluminum is abundantly found in the Earth’s crust. Alumina is refined from Bauxite, smelted, mixed with other elements and cast into billets or logs. Aluminum alloy composition varies based on the type and the amount of additives made to the aluminum. The cast aluminum is the raw material used for the aluminum extrusion process.
Tooling used to make the required profile is called an aluminum extrusion die. Made of steel, the die has an opening (or possibly several) in the shape of the desired profile. Each unique profile requires its own unique tooling.
The aluminum extrusion process is greatly heat dependent. Monitoring temperatures from beginning to end is critical to ensuring aluminum alloy properties such as tensile and yield strengths are met, as well as affecting the final finish of the part.
The aluminum extrusion process begins by heating the billets or logs to 400-480°C (750-900°F). The aluminum alloy is still solid but malleable. It does not glow when heated; aluminum looks the same whether hot or cold.
The heated aluminum billet is transferred to the press container. Pressure is applied to the billet by a hydraulic ram forcing the aluminum to fill the container.
The pressure inside the container increases, forcing the aluminum alloy through the opening(s) in the aluminum extrusion die. The result is a long length of consistently shaped aluminum, the aluminum extrusion, emerging from the other side of the die.
The rate at which a shape is extruded depends on such things as the weight/ft of the part, difficulty of the profile, wall thickness, aluminum alloy selection and/or the number of cavities or openings in the aluminum extrusion die.
With the aid of the puller (a jaw-like piece of machinery that clamps onto the material and guides the aluminum extrusion as it emerges from the die) the extrusion extends along the run-out table. The length of run-out depends on the weight per foot of the profile and the number of cavities in the die.
As the aluminum extrusion emerges from the die, the temperature is in the range of 510-550°C. Cooling the aluminum extrusion is assisted by the use of fans and/or water spray or a full water quench. Aluminum must cool at a specified rate in order to meet aluminum alloy properties. Temperatures are measured numerous times throughout the process to ensure targets are met.
Long lengths of aluminum extrusion are mechanically transferred to the cooling table to cool to room temperature. Cooled lengths are then stretched. Stretching is a mechanical process whereby aluminum extrusions are stretched to make the part straight.
Stretched parts are cut to lengths typically between 6 and 30 feet depending on order requirements. Shorter lengths and tight tolerances require secondary cutback in fabrication.
The final “hot” step is to artificially age the aluminum extrusions to bring them to the required hardness. They are, basically, “cooked” in a large oven for up to 8 hours. Aluminum will harden or age naturally on its own; artificially ageing shortens the process time.
Aged material is ready to ship to the Customer or move on for additional processing such as fabrication and/or finishing.