All about extrusion
Aluminum extrusion is a product that is formed using a temperature dependent process where aluminum billet is pushed through a die with desired shape. The process is very similar to a child’s Play-Doh extruder where the material is forced through the shaped opening.
Benefits of extrusion
- Suitable for complex, integral shapes
- Produced to close tolerances
- Produced with uniform quality
- Short production lead times
- Suitable for a wide range of finishes
- Virtually seamless
- Easy to fabricate
- Joinable by various methods
- Suitable for easy-assembly designs
Aluminum extrusion process
The aluminum extrusion process is greatly heat dependent. Monitoring temperatures from beginning to end is critical to ensure aluminum alloy properties such as yield and tensile strengths are met, as well as affecting the final dimensions and finish of the part.
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 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.
Some key factors that influence the rate
at which a shape is extruded are:
- Weight/ft of the part
- Difficulty of the profile
- Wall thickness
- Aluminum alloy selection
- Number of cavities
- Number of hollows in the profile
With the aid of the puller which is 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. At times the run out can be upwards of 150 feet.
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 the desired aluminum mechanical properties once tempered. Temperatures are measured numerous times throughout the process to ensure requirements are met.
Long lengths of aluminum extrusions are mechanically transferred to the cooling table and cooled to room temperature. These cooled lengths are then stretched using a mechanical process, to straighten the profile as well as align the grain structure.
Stretched parts are cut to lengths typically between 8 and 24 feet depending on order requirements. Shorter lengths and tighter cutback tolerances require secondary cutback in fabrication.
The final “hot” step is to artificially age the aluminum extrusions in a temper oven to bring them to the desired mechanical properties. 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, mill finished, long length material, is ready to ship to the Customer or move on for additional value add processing such as fabrication and/or finishing.
Extruded product flow
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