Aluminum extrusion is a versatile metal-shaping process in which a machine guides aluminum through a shaped opening in a die. This process results in an elongated piece of aluminum formed into the shape of the die. The extrusion process allows for the creation of a wide range of complex, custom metal shapes.
The Extrusion Process
Extrusion is a multi-step process. Once the design for the desired part shape has been finalized, production can begin. It’s critical to have a solid understanding of the exact requirements for the part, as the intended function, look, and environment of the product will determine which alloy is used to create it. Different aluminum alloys offer distinctive features and benefits; therefore, some alloys will be better suited than others for specific applications. Once the alloy and design are selected, a die is produced in the needed shape, as well as any other tooling required for the press to make the new part.
To begin the actual extrusion, a heat treatment is applied to a billet — an unshaped bar of aluminum — to soften the metal and make it more pliable. The temperature of this heat treatment is usually between 800 °F and 925 °F. The softened billet is then placed into a hydraulic press, where a lubricant is applied to the billet and ram in order to prevent them from sticking to one another. (The ram is an arm of the press that pushes the billet through the machine.) As the ram starts to apply pressure to the billet in a container within the press, the ram begins to compress the softened billet against the die, and the billet becomes shorter and wider in the container. The pressure gradually pushes the billet until it squeezes through the die, emerging on the other side in the desired shape.
Once the extruded metal reaches its desired length, the die is cut with a profile saw or shears, and excess material is recycled. After the extruded aluminum metal cools, a stretching machine is used to straighten and increase the metal’s hardness and strength. After the stretching stage, the extrusion is cut into smaller lengths to form individual parts. These parts then undergo “aging,” a process that speeds up the aging process with controlled temperatures to increase the metal’s hardness and durability. Other treatments may then be applied to the extruded aluminum parts to imbue them with certain properties or performance capabilities before being sent out for packaging and shipping.
Aluminum Extrusion Alloys
Several aluminum alloys can be used in the aluminum extrusion process, such as the 1000 series, 6000 series, and 7000 series — each offering different qualities that make them ideal for specific uses.
The 1000 series of alloys is non-heat treatable and has low strength; these alloys are often used in products requiring high thermal and electrical conductivity. The 6000 series is heat treatable, has medium-to-high strength, is easy to weld, and resists corrosion well. The 6000 series alloys hold up well under the extrusion process and, as a result, are the most commonly extruded material in load-bearing constructions. The 7000 series, meanwhile, offers the highest strength of the alloys most widely used in construction materials. The 7000 series alloys are easy to weld and lose less strength in areas affected by heat than the 6000 series. The 7000 series alloys are commonly used in automotive parts, aircraft containers, bicycle frames, and speedboats.
Benefits of Aluminum Extrusion
Aluminum extrusion offers a range of unique benefits, particularly in comparison to die casting, another popular method for shaping metal.
In die casting, molten metal is injected into a mold, which is known as the die. For easy visualization of the process, picture pouring batter into a tin in order to make a cake; the batter is the molten metal, the tin is the die, and the final product — the cake — is the complex shape produced. These intricate shapes can include complex cross-sections. Extrusion also allows for the working of very brittle materials, since the material only deals with shear and compressive stresses.
While die casting serves as a versatile, reliable process for many applications and industries, extrusion is much more cost-effective due to the lower tooling costs involved. Plus, parts made with the extrusion process can be just as strong and rigid as those created using die casting. And extruded parts actually have higher ductility than those made using the die casting process. In general, die casting is better suited to applications requiring parts that do not have uniform cross-sections.
Below are a few of the main benefits offered by aluminum extrusion.
- Ability to meet high production volumes
- Cost efficiency
- Ability to work many types of materials
- Creation of complex, intricate parts
- Ability to work brittle materials
- Continuous process
Common Aluminum Extrusion Applications
With so many options available for customizing the shape and characteristics of aluminum, it’s little surprise that aluminum extrusions have applications in a wide range of industries. Extruded aluminum products can be found in transportation, electronics, automotive, renewable energy, construction, and telecommunications fields, among many others.