The Aluminum Extrusion Process: Common Methods, Characteristics & Applications
Once rarer than gold or silver, aluminum has become ubiquitous in its applications ever since a nineteenth-century chemist discovered a method to isolate it. The most widespread element of the earth’s crust, aluminum recycles easily, doesn’t rust, and conducts heat and electricity.
Combined with other metals to formulate an aluminum alloy, aluminum demonstrates a high performance standard across many industries. The process of aluminum extrusion transforms aluminum alloy into products for countless uses. In fact, aluminum extrusions appear in electronics, transportation, architecture, telecommunications, renewable energy—virtually everywhere.
So, what exactly is the aluminum extrusion process? And where can you find custom aluminum extrusions in the grade, temper, and shape your company needs?
Extrusion dates to 1797, when an English inventor, Joseph Bramah, patented a process to manufacture lead pipes. His process used a plunger to manually force soft metal through a die, which he called “squirting.”
Two years earlier, Bramah also patented the first hydraulic press. In 1820, Thomas Burr combined Bramah’s inventions, adding the hydraulic press to the squirting process to manufacture lead pipes. As aluminum became more readily available in the late nineteenth century, the process evolved to take advantage of this versatile metal.
When you decorate a cake, your hand forces icing through the piping bag and out through a decorative tip. The icing emerges in the shape of the tip’s opening.
The aluminum extrusion process is very similar. The “icing” is a block of metal known as an aluminum billet. A ram forces the billet through a container to the die, a steel disk with an opening in the shape of the desired cross-section. The extruded aluminum shape that emerges from this meticulous process is the aluminum profile.
In 1894, Alexander Dick invented the hot extrusion process that continues to be in wide use today.
During hot extrusion, temperatures range from 375 to 500 degrees Celsius. The aluminum, which has a boiling point of 660 degrees, becomes soft but not liquefied.
To create the desired profile, a hydraulic press exerts 100–15,000 tons of pressure. The billet crushes against the die and, restricted by the container walls, squeezes through the opening.
The extruded material is quenched, cooled either by a water bath or by fans. A hot saw shears the extrusion to table length, and it cools to room temperature. Because natural twisting occurs in hot extrusion, the profile then moves to a stretcher. A mechanism grips it on both ends and pulls to straighten the extrusion.
Last, the profile moves to another area to receive a surface finish, such as painting or corrosion resistance. The extrusion may be additionally cut, bent, assembled, or directly packed for shipment.
The process of aluminum extrusion affects the temper of the aluminum alloy used. Temper refers to variations of an alloy’s physical properties. In other words, the alloy’s strength and hardness can change depending on quenching, heating, and other techniques of the extrusion process.
Even though hot extrusion is the most common for aluminum, today’s process can also be warm or cold. The type and end-use of the product determine the best method to use.
Hot extrusion renders the metal more malleable. This enables the production of very complex shapes.
Cold extrusion, which takes place at room temperature, is generally a faster process that requires minimal surface finishing. However, the metal must have a high degree of ductility, or capability to deform in response to stress without being heated.
Warm extrusion heats the aluminum below its recrystallization point, so the metal is more malleable than it would be in cold extrusion but also requires more force than hot extrusion.
Extrusion can also move in either direction. In the more common direct extrusion, or forward extrusion, the die is stationary. The extrusion press forces the billet through the mold into the desired shape.
However, the amount of force required to force the billet through the container results in relatively high friction. The friction also results in an increase in temperature along the length of the extrusion.
The change in friction and temperature of the extrusion press can change the microstructure of the shape, meaning the arrangement and structure of its lattice at the molecular level. Microstructure affects the machinability of the profile, such as its hardness or yield strength.
By contrast, indirect extrusion is a backward extrusion process. Rather than the die remaining stationary, it is the billet that doesn’t move. Instead, the ram forces the die to apply pressure on the stationary billet.
Because the billet doesn’t move, there is no friction with the container, so the force and temperature remain relatively constant from front to rear. This results in a more consistent microstructure.
However, because there is no friction to remove impurities on the surface of the billet, it must remain free of dirt and oil. Generally, this means that the billet can’t be used directly out of the foundry, or in its “as-cast” condition. Instead, the as-cast surface layer must be removed before extrusion.
Aluminum extrusions offer a range of desirable characteristics that other alloys don’t provide.
The strength of aluminum relative to its mass has proved beneficial across varying industries, most notably aerospace.
Aluminum alloys are available from distributors such as Diversified Specialty Metals in a wide range of strength values. Furthermore, the design of the aluminum extrusion shapes can concentrate strength to meet your project’s needs.
Aluminum has a high resistance to corrosion. This is because when aluminum atoms are exposed to oxygen, a thin, invisible layer of aluminum oxide forms. This aluminum oxide layer is chemically inert, meaning it is not reactive with water molecules that could otherwise cause rust.
Pound for pound, aluminum has twice the electrical conductivity of copper. That makes aluminum extrusions very effective for use as electrical connectors or busbars, which are metallic strips used in power distribution.
Aluminum extrusions also conduct cold and heat more effectively than other metals considering their weight. Therefore, any project that involves heat dissipation or exchange benefits from the use of aluminum extrusions, such as housings for electronics or other instruments that emit heat.
Aluminum extrusions do not emit sparks, making them ideal to use with any project involving explosives or other flammable materials.
Aluminum extrusions often fit together without mechanical connections. As a result, profiles often feature greater overall strength than assemblies that must be joined mechanically. Also, extrusions are less prone to leaking or loosening over time.
There are three main categories of profiles:
Solid profile: no opening, or “void.” Solids are easier and faster to extrude and thus are generally less expensive. Examples include rods, beams, or angles.
Hollow profile: complete void somewhere in the cross-section, such as a square or rectangular tube.
Semihollow profile: partially enclosed void. Semihollow extrusions are usually circular or rectangular with a gap on one side, such as a C channel.
Diversified Specialty Metals offers aluminum tubes, bars, and other profiles in many different grades and shapes. For instance, you can find square, rectangular, and round tubes as well as aluminum bars that are square, round, hexagonal, or angled.
Many industries make use of standard as well as custom aluminum extrusions:
Architectural structures: railings, canopies, bleachers
Electrical systems: solar panels, lighting grids, busbars
Interlocking displays: picture frames, pop-up booths
Factory support equipment: tables, benches, carts
Transportation: aerospace, automotive components
As one of the few Canadian companies with an AS9120B certification, Diversified Specialty Metals holds all our aluminum extrusion products to the highest quality standards.
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