The simplest definition of aluminum extrusion is an exclusive procedure where aluminum alloy is forcefully passed through dies with unique cross-section profiles. To help you understand how it works, picture squeezing toothpaste out of a tube with a circular opening. The extruded material will match the profile of the tube’s circular opening.
The force exerted by your fingers is replicated on an industrial scale by a ram. Ideally, a strong ram pushes aluminum across the die, subsequently emerging from the exclusive die’s opening. Once it goes through, the resulting product features a similar shape to the die and is removed along an exclusive run out table
The cross-section of the die used in aluminum extrusion is designed to create specific shapes and molds, which is why extrusion is commonly used in product design. Some of the most commonly extruded shapes include round tubes, angles, and channels.
Extrusion can make simple shapes like the ones mentioned above, but it is also capable of creating very complex designs.
We can categorize these shapes into three distinct classes:
· Solid extrusions – These extrusions don’t have any openings or voids. Examples include rods, beams, and angles.
· Hollow extrusions – Hollow extrusions contain one or more voids. Examples include circular, square and rectangular tubes.
· Semi-hollow extrusions – These extrusions have a partially enclosed void. Examples include C-shaped channels.
Extrusions can also be formed into complex shapes, chiefly for architectural applications.
Unlike simple shapes, architectural shapes may be made up from multiple extrusions, typically consisting of interlocked shapes. Some extrusions may even be fitted with a polyamide thermal break, a feature that facilitates better insulation.
We can explain the extrusion process in ten steps.
The die used in this process is made from H13 steel. That is, if you don’t already have ready die in your warehouse.
Once machined or shipped from your warehouse, it is preheated to 450 – 500 degrees Celsius. Heating the die ensures the even flow of the aluminum and extends its lifespan.
After preheating, the die is then placed inside the extrusion press.
A billet is a cylindrical block of aluminum alloy cut from a solid log of alloy material.
Like the die, this billet is preheated to around 400 – 500 degrees Celsius to improve the extrusion process.
This is the perfect temperature to make it malleable (and easy to extrude) but not molten.
The preheated billet is mechanically moved to the press to begin the extrusion process.
Before loading it into the press, a film of lubricant is smeared onto the billet, die, and extrusion ram.
The purpose of this lubricant is to stop the billet from sticking to either the ram or the die.
What follows is the extrusion process described earlier in this article.
Once the billet has been moved into the press, the ram applies pressure rated at fifteen thousand tons to force it through the die.
The pressure forces the billet into the press’s container where it expands and fills the walls.
The billet only starts to be pressed against the die when it fills up the walls of the extrusion container.
As continuous pressure is applied, the aluminum is forced out the die’s opening(s).
If successful, the extrusion emerges looking like the die’s cross-sectional profile.
As it emerges, a puller grips the material and guides it through the runout table.
The runout table moves at a speed that matches the exit of the extruded material.
As it moves along the runout table, a bath of cold water or overhead fans are used to cool or “quench” the extrusion uniformly.
When it reaches maximum runout table length, a saw is used to shear it so that it can be separated from the press.
Even though it is quenched as it runs along the runout table, the extrusion is still hot and requires further cooling.
Once sheared to table length, quenched extrusions are now cooled until they reach room temperature.
The extruded aluminum is moved mechanically and moved to the cooling table.
It is left there until it cools to room temperature.
During the cooling process, the extrusion tends to twist naturally. Fortunately, this is corrected by stretching it.
It is then transferred to a mechanical stretcher, which grips it on each of its ends and pulls it to make it completely straight or up to specifications.
Once straightened and work-hardened, aluminum extrusions are ready for cutting to the desired lengths.
The extrusion is now taken to the table saw and cut to pre-specified dimensions. Usually, these lengths vary from 8 – 21 feet, and the extrusions have a T4 temper.
Once cut, they are sometimes placed in an aging oven where they “age” until they achieve higher tempers such as T6 or T5.
Following the extrusion process, the aluminum may be taken through further processes to enhance its performance.
The most important process is heat treatment, which enhances properties like tensile strength and yield stress.
In this accelerated aging process, profiles are placed into an oven and brought to T5 or T6 tempers.
The properties of treated and untreated aluminum are very different. Untreated aluminum (T4) aluminum has a tensile strength of 35,000 psi (241 MPa) whereas heat-treated aluminum (T6) has a tensile strength of 45,000 psi (310 MPa).
After heat treatment, aluminum extrusions are ready to be finished and fabricated.
Most finishing operations are designed to enhance corrosion properties and improve the appearance of the material.
One such process is anodization, which thickens the naturally-occurring oxide layer on the material, improving corrosion and wear resistance, and creating a porous surface that readily accepts dyes.
Painting, sublimation (creates a wood finish), sandblasting, and powder coating are other processes used to finish aluminum extrusions.
It is important to understand the tensile strength requirements for any project to ensure the use of the right alloy and temper.
Aluminum extrusion is one of the most important manufacturing processes in practice today.
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