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This article is an investigation of the aluminum extrusion process and its basic elements.
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Extruded aluminum is a metal shaping process that involves forcing a preheated or cold aluminum billet through a die profile that has a specific cross-sectional shape. It is a method for manufacturing aluminum components that begins with a two-dimensional profile that has the necessary width, height, and thickness. The third dimension of a profile is determined by post extrusion processing, which includes pulling the profile out onto the runout table and cutting it into appropriate lengths.
The two ways that aluminum can be extruded are hot heading and cold heading. With hot heading, the billet is heated to approximately 25% below its melting temperature. With cold heading, the billet is extruded at room temperature. Both methods of extrusion have their benefits. Hot heading is a faster process, while cold heading produces more durable and long-lasting products.
Extruded aluminum is the most cost-effective manufacturing process. It is capable of producing products with exceptional tolerances, precision, and accuracy. Every extruded profile has the same dimensions, from the first extruded part to the last, without any variations in length or measurements.
Aluminum is desirable due to its light weight, high strength, and corrosion resistance. In its pure form, it is soft and has low strength. To improve its mechanical properties, it is usually alloyed with elements such as copper, magnesium, manganese, and silicon. Furthermore, it can be heat treated to further improve and attain the right balance of strength and ductility.
The first development of metal extrusion happened in the late 1700s when the first patent for the forming process was filed by an English inventor and locksmith, Joseph Bramah. The process was originally made to create lead pipes and lead sheathing of cables. This early process of extrusion could work soft metals.
Harder and stronger metals, such as aluminum, require higher forming temperatures and pressures. Aluminum was not used as an extruded material until the introduction of the hot extrusion process by Alexander Dick in 1894.
Today, aluminum extrusion is widely used, with a global market size of more than $67 billion that is expected to grow by 3.8% annually from 2020 to 2027. The main applications of extruded aluminum are in the fields of building and construction, automotive and transportation, consumer goods, and electrical and energy.
Aluminum is the most popular metal used for extrusion forming. This metal offers distinctive combinations of mechanical properties, such as high strength, low density, and good workability. These qualities are almost constant at all temperatures. Moreover, other desirable properties, such as electrical conductivity, reflectance, paramagnetism, etc., further widen its areas of application.
The extrusion process has its advantages which, when in tandem with the properties of aluminum, produce products with unique qualities. These qualities are both beneficial for the manufacturer and end-user. The extrusion process is mainly used for producing parts with complex cross-sections. Additionally, it can also work with brittle materials that are difficult for other forming processes.
The standard finish is mill finishing, where the product is deburred and cleaned and made ready for anodizing, powder coating, or other secondary surface finishing. Sandblasting is a common surface treatment completed before anodizing. The types of anodizing finishes include clear and black, which are the most common anodizing finishes, with custom colors also available.
Anodizing is a finish that combines to the underlying aluminum with unmatched adhesion. The finishes are chemically stable, non-toxic; and heat-resistant. The thickness of anodizing is 6 μm to 18 μm and comes in black or clear, with customized colors available. The limitation of the anodizing process is the length of the extrusion since long extruded aluminum will not fit in the anodizing tank. Electrostatic spray coatings are also used to coat extruded aluminum and produce the highest quality products in a variety of colors.
Extrusion is categorized as a bulk-forming process where there is a significant change in the surface-to-volume ratio of the formed metal. This is achieved by subjecting the billet to compressive forces with the help of rams, punches, tools, and dies. To produce the desired profile with a predictable grain structure, the plastic theory is applied to determine the mechanics of the metal‘s plastic deformation mechanics.
The formed product largely depends on several variables. The main variable is the extrusion pressure, which is influenced by other factors such as temperature, extrusion ratio, and extrusion speed. The extrusion variables are enumerated below.
The most widely used alloy for extrusion is the 6xxx series alloy.
The manufacturing of aluminum extrusions starts with the production of aluminum billets that is fed to the extrusion machine. Aluminum is refined from bauxite to produce alumina or aluminum oxide. The oxygen is then separated from the aluminum through a reduction process to create pure aluminum. The virgin aluminum is then smelted into ingots which will be used to create billets and recycled aluminum.
Aluminum billets are supplied to manufacturing plants to create end-use parts through various metal forming processes. Aluminum extrusion usually involves heating the billet to increase the plasticity of the metal. The heated billet is then loaded into a cylindrical chamber with a ram on one end and a die on the other. The ram is driven either mechanically or hydraulically to produce enough compressive force. The pressure is applied to plastically deform the billet, forcing it to flow through a die. The setup can vary depending on the type of extrusion process used.
Aluminum extrusions can be produced through different processes. These can be categorized according to the method of applying pressure to the billet, as summarized below.
As described by the graph, at the start of the extrusion, the required pressure starts to increase rapidly to its peak value known as the breakthrough pressure. Once the flow is initiated, the pressure decreases, and steady-state extrusion proceeds. When the loaded billet is almost consumed, the extrusion pressure reaches a minimum value, followed by a sharp rise as the remaining is compacted. The remaining billet that is not extruded is called the butt or discard, which is 5 to 15% of the billet.
As seen in the graph, the required pressure only rises to the steady-state extrusion pressure. Indirect extrusion proves to be a more energy-efficient process than direct extrusion. Despite this advantage, indirect extrusion fails to be a replacement for direct extrusion. This is because of the requirement to use a hollow ram which is weaker compared to a solid press. This limits the loads that can be applied to compress the billet. Hence, this process is only applicable for producing extrudates with small cross-sections.
Hydrostatic extrusion offers the best of both worlds from direct and indirect extrusion. This process solves the problem of the high frictional forces experienced in direct extrusion and the limitation on the cross-sectional area of the indirect process. However, they also suffer from disadvantages such as lower throughput due to the longer preparation per extrusion cycle and sealing difficulties at high pressures. Lower throughput is the consequence of the additional billet tapering process and the necessary injection and removal of fluid for every cycle. In some setups, instead of removing the fluid, the discard is retained to prevent the sudden release of the extrusion fluid. This discard is usually tougher due to cold working and will require additional compression to extrude. Sealing difficulties are from the tighter seal between the chamber and ram and the seal between the billet and die.
Aluminum extrusion is usually done under elevated pressures to increase the tendency of the metal to flow plastically. However, other technologies enable the process to be done at room temperature.
Enumerated below are the classifications of the extrusion process according to the direction of metal flow relative to the motion of the ram.
Obviously, the aluminum extrusion process is complex. Luckily, there are many manufacturers of extruded aluminum equipment in the United States and Canada that have essentially perfected this process. Below, we feature many of these manufacturers and their machines.
Description: The SMS SmartExtruder is a specific model produced by SMS Group. It is a technologically advanced extrusion machine designed for high productivity and efficiency in aluminum extrusion. The SmartExtruder offers features like intelligent control systems, energy-efficient operation, precise temperature control, and advanced automation capabilities. It is known for its versatility in handling a wide range of extrusion profiles and achieving consistent quality.
Description: Presezzi Extrusion Group offers the Series 7 Extrusion Press model, known for its advanced design and high precision. It features state-of-the-art automation, excellent control over the extrusion process, and energy-efficient performance. The Series 7 press offers versatility in handling various extrusion profiles and alloys, enabling reliable and high-quality production of extruded aluminum.
Description: UBE Machinery manufactures the UBE Aluminum Extrusion Press, known for its advanced technology and superior performance. This model incorporates precision control systems, efficient energy utilization, and high-speed capabilities. UBE's Extrusion Press offers versatility in handling different aluminum alloys and extrusion profiles, ensuring precision and reliability in the extrusion process.
Description: HPM (Hamilton Plastic Molding) is a renowned manufacturer of industrial machinery, including aluminum extrusion presses. Their HPM Aluminum Extrusion Presses are designed for high productivity and precision. These machines offer advanced control systems, efficient energy consumption, and the ability to handle various extrusion profiles and alloys. HPM presses are known for their robust construction and reliability.
Description: SMS Elotherm specializes in induction heating systems used in aluminum extrusion processes. Their Induction Billet Heating Systems offer precise and efficient heating of aluminum billets. These systems incorporate advanced induction technology, precise temperature control, and energy-efficient operation. SMS Elotherm systems are designed to achieve uniform heating and optimal billet malleability, ensuring high-quality extrusions.
Please note that the availability of specific models may vary over time, and it's advisable to consult manufacturers directly or refer to their product catalogs for the most up-to-date information on the models and features offered for producing extruded aluminum in the United States or Canada.
In the design of aluminum products, there are several different alloys to choose from. The choice of an alloy is the first step in creating a quality extruded aluminum product. Included in the choice of an alloy are the many processes used to perfect the strength of aluminum extrusion with heat treatment being restricted to heat-treatable alloys. Additionally, the tempering of an alloy can determine the strength and durability of an aluminum alloy extrusion.
Tempering is a process that involves mechanical, chemical, or thermal treatment of extruded aluminum. It can include softening or annealing, cold working, or spring tempering. There are five forms of tempering for aluminum, each of which is designated by the letters F, O, H, W, and T, with certain tempers having subdivisions. The various letters of the tempering designations refer to the potential physical properties that can be achieved.
Aluminum alloys in the series of 1xxxs, 3xxxs, and 5xxxs are not heat treatable, while series 2xxx, 6xxx, and 7xxx are heat treatable, and series 4xxx contains heat treatable and non-heat-treatable ones. The strength of non-heat-treatable alloys depends on their properties and cold working. The alloy groups' chemical makeup and metallurgical structures determine how the alloys will be fabricated.
All aluminum products are differentiated by their properties as well as their alloy and temper designation. This aspect of extruded aluminum is critical to understand when deciding on what aluminum alloy will be used to produce an extruded aluminum profile. Although the different processes are an important part of the selection process, the type of aluminum alloy and its temper designation are essential and important factors that have to be considered.
Alloy designations are four-digit numbers, that identify the alloy’s chemistry. The first digit indicates the primary alloying element, such as copper, manganese, silicon, or zinc. The designation for pure aluminum is the first in the series and begins with the number one. The second number indicates a change to one of the alloying elements. The last two digits of the series, numbers 3 and 4, identify the specific alloy used, except for the 1xxx series, where the last two digits specify the aluminum content between 99% and 100%.
Aluminum Numbering System as Established by the Aluminum Assciation 1xxx Pure Aluminum 2xxx Copper 3xxx Manganese 4xxx Silicon 5xxx Magnesium 6xxx Magnesium and Silicon 7xxx Zinc 8xxx OtherTemper identifications are alphanumeric and are added with a dash after the alloy series number. The letter of the temper designation describes how the alloy has been altered mechanically and thermally treated. The letters of the temper designation indicate the class of treatment.
The main purpose of tempering is to enable designers to achieve desired mechanical properties. The strength of an aluminum alloy can be significantly enhanced from a few thousand to several through the use of tempering. This increased strength is possible using a combination of solution heat treatment and artificial aging. Tempering can also change an alloy's characteristics and how it will react to different fabrication processes.
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