History of Aluminum Extrusion
Aluminum extrusion, or the extrusion process, owes its beginnings to three men – Joseph Bramah, Thomas Burr, and Alexander Dick. Each of them advanced and perfected the process so that inventors from the industrial revolution could improve it. Though the goals of these men may not have been to create aluminum extrusion, they did take the first steps in developing the extrusion process.
Joseph Bramah, locksmith, inventor of the hydraulic press, and originator of extrusion, patented the first metal extrusion process in 1797. With Henry Maudslay, an engineering genius, Bramah developed a process for forcing soft metals through a mold using a hand driven plunger. His reason for using the process was to create parts for producing unpickable locks. The initial use of the process led to the creation of other tools, which marked the beginning of metal extrusion.
Impressed with Bramah’s extrusion process and his hydraulic press, Thomas Burr, in 1820, combined the two inventions to develop a hydraulic press to force metal through a die. Burr’s goal was to extrude lead pipe using a faster and more reliable process. At the time, extrusion was named "squirting".
The present process of hot extrusion dates back to 1894 when Alexander Dick melted non-ferrous metals to be forced through a die. Though there have been many changes over the last hundred years, the design and developments of Dick, Bramah, and Burr remain the foundation for the modern extrusion process.
The discovery and early uses of aluminum
Aluminum is the perfect metal for the extrusion process since it can be extruded either hot or cold. Its high resistance to chemicals, rust, and corrosion has made it the solution for the manufacture of many of today’s products. Though aluminum is one of the most common metals on earth, it took centuries for a process to be developed to make the production of aluminum practical and affordable.
In ancient times, alum was used for hide tanning, first aid, fabric dying, pickling, canning, and many other processes. In its natural state, alum appears as a salt of either potassium aluminum or ammonium aluminum sulfate. It is still used today as a supplement to medicines.
Alumina, a form of alum, was discovered in 1825 by Danish scientist Hans Christian Oersted. Though it was known to exist, the refining and processing of it was extremely difficult making aluminum more valuable than gold, which continued until 1887. In 1886, Oberlin college student Charles Martin Hall and French engineer Paul Heroult, working in different parts of the world, developed a smelting process for aluminum involving electrolysis. The Hall-Heroult process made aluminum easily accessible and brought the price of it down opening the door for its mass production. A year after Hall and Heroult’s advancements, in 1887, Karl Josef Bayer discovered a chemical process for extracting aluminum from bauxite. Though the innovations of these three men are over a hundred years old, they are still used for the modern production of aluminum.
The sharp rise in the uses and applications of aluminum was spurred by the first extrusion press in the United States that was built in Pennsylvania in 1904. Its invention became a major asset for the growing airplane and automotive industries.
In a twist of history, a Swiss student, Robert Viktor Neher, developed a method for processing thin sheets of aluminum in 1910. At the time, ballooning was popular, but many balloons lost air due to the thinness of their fabric. Neher came up with the idea of pressing aluminum so thin that it could be placed over the fabric of the balloon to close any holes. His discovery led to today’s aluminum foil.
During World War Two, aluminum became an essential part of the war effort and was used to make several of the items soldiers and sailors used. "Aluminum for the Defense" and "Tinfoil" drives were held for contributions of aluminum for recycling. From 1940 until the end of the war, of the 296,000 aircraft produced, more than half were made with aluminum.
The exploration of space began with a beach ball sized satellite named Sputnik I launched by the Soviet Union in 1957. The outer shell of the satellite was covered in an aluminum alloy that could withstand the heat and friction of launching into space. The use of aluminum for the creation and manufacture of space vehicles increased the need for aluminum production.
The modern aluminum can began in 1959 with the Coors Brewing Company in Colorado. They introduced an all-aluminum, seamless, two piece can for distribution of their beer. In conjunction with the new can, Coors instituted a recycling program where every can returned to the brewery was worth one cent. The soft drink industry began using aluminum cans in 1964 when Royal Crown Cola, from Columbus, Georgia, introduced them.
Since its beginnings in the late 19th Century, aluminum has become a vital necessity to many industries from household products to airplanes and cars. It is hard to imagine modern society without it.
Aluminum extrusions are linear products valued for their high strength-to-weight ratio and the low cost of the extrusion process. Aluminum can be extruded either hot or cold. Extrusion produces strong and lightweight shapes of varying angles, beams, channels, and profiles as well as different sizes of tubing. Complex designs can be produced with precision tolerance to interlock with channels and other aluminum structures. Since aluminum is strong and resistant to extreme temperature variances and rust, it has become the first choice for the construction and building industries.
Aluminum extrusion can be hot, warm, or cold. The selection of the appropriate process depends on how the fabricated piece will be used and the type of product. Of the three processes, hot extrusion is the most extensively used since final products tend to have greater strength and tolerance. Warm extrusion is performed at above room temperature while cold extrusion is done at room temperature or slightly below. All three processes involve forcing aluminum through a die.
All extrusion processes involve shaping using a die in the form of the cross section. Dies are thick, circular disks with one or several openings that create the profile. They are made from steel that is heat treated to withstand the pressure and temperature of hot aluminum. When raw aluminum is forced through the die, it takes 100,000 to 125,000 psi to push it through. Though there is a limitless number of die shapes, they all fall into three basic types: solid, semi-hollow, and hollow. Solid dies produce shapes with no openings in the middle while hollow dies have one or many openings and semi-hollow dies are nearly hollow.
The life of an aluminum die depends on its original design since the buildup of pressure and heat can produce a great deal of wear. Dies need to be able to withstand uneven pressure and control the amount of heat. Over time, dies wear out. Fortunately, the low cost of the extruding process makes up for the expense of replacing them. Profile design, tolerance settings, and adjustments for the types of alloys can significantly help in extending a die’s use.
The feedstock for the extrusion process is referred to as a billet or log, which can be square or circular. It is forged by taking pure aluminum and combining it with other metals to form an alloy. The combined metals are smelted to remove impurities. The molten mixture is poured into a form where it is placed under high pressure to remove any air or gases and to align the molecules. The final result is a solid block of aluminum ready for extrusion.
During extrusion, the billet is heated to temperatures of 800 to 925o F above the recrystallization temperature to keep it from hardening, which makes it easier to push through the die. Once heated, it is moved to the loader where a thin film of lubricant, which can be oil or graphite for cool extrusions and glass powder for hot ones, is added to keep it from sticking to the equipment before being placed in the cradle.
The ram pushes the billet crushing it against the die. As the molten aluminum is forced through, liquid nitrogen cools it, which helps to increase the life of the die. As the extrusion exits the die, it is pushed to the lead out table and puller, which guides it down the table. As the extrusion is pulled, it cools. At the desired length, the extrusion is cut and placed on the cooling table. After it cools, it is stretched to increase its hardness. The final step of the process is to cut the fully processed extrusion to the desired length. In some cases, there may be a need for extra finishing, buffing, or trimming. Those processes depend on the requirements of the final product.
In cold extrusion, the part is formed by moving the aluminum through the die at room temperature. The necessary force to move it through the die has to exceed the strength of the aluminum to ensure proper deformation. Cold extrusion produces parts with close tolerance, high strength, and requires minimal finishing. Though there are several methods of cold extrusion, for most manufacturers, there are three basic types – forward or direct, backward or indirect, and upsetting.
For forward or direct cold extrusion, the ram forces the billet through the die. The billet is placed in a heavily walled container for the ram to force it forward. With backward or indirect cold extrusion, the metal moves upward into the descending die, which requires greater pressure. Upsetting cold extrusion is normally a part of backward or forward cold extrusion and performed at right angles to the workpiece or billet.
With warm extruding, the billet is heated to temperatures ranging between 800o F to 1800o F. The ideal range is 1000o F to 1330o F. In either case, these temperatures are below the recrystallization temperature, which enhances the ductility of the billet while keeping it solid. Less force is required with warm extruding to move the billet through the die.
A crucial part of the extrusion process is the maintenance of the temperature for both the billet and the die. Controlling the billet feed and exit temperature improves the quality of the final product. In many situations, the operator is responsible for ensuring the temperature is correct and determining the quality of the finished product. With closed looped systems, the control of the profile temperature is electronically controlled to keep it consistent and increase extrusion speed.
Types of Extrusions
Extrusion is a part of so many industries that it is not possible to create a complete list of every one of its types. The descriptions below contain a very general overview of the various kinds of extrusion and their use. A more complete set of information can be found at the various manufacturer’s websites.
The standard extruded aluminum angle is a L-shaped part with two legs that are formed by bending the extrusion to a 90 degree angle. Aluminum is an ideal metal for the manufacturing of this long, narrow shape because of its high strength-to-weight ratio and corrosion resistance. The legs of the angle are either equal or unequal and have sharp corners. The bent L-shape extends the length of the material creating horizontal and vertical flat surfaces that add strength to the unit in both directions. L-shaped components are used as structural support. In the building industry, they are referred to as aluminum angle irons or aluminum angle bars.
Aluminum beams are large, oblong pieces of metal, constructed from aluminum alloys, and are used as horizontal support in building construction. Aluminum beams are a preferred alternative to steel, which is stronger but heavier and wood is lighter but weaker. Structural Aluminum is used for beams because of its light weight, which makes it easier to install. Structural aluminum is weather resistance, doesn't corrode quickly, is able to withstand high and low temperatures, and doesn't rust when exposed to water. Aluminum beams last longer without any need for maintenance or upkeep and come in different shapes including unequal or equal I beams, the most commonly used, unrounded and C-shaped channels, H beams, and T beams.
One of many extruded aluminum shapes is aluminum channels, which are smooth, linear, and narrow. Channels provide support framing for roll formed products and are ideal for engineering and structural applications such as light building frames, frame extensions, light poles, lighting fixtures, window frames, car bumpers, hardware joints and boat dock ladders. They have high electrical conductivity and are good heat conductors and reflectors, making them ideal for heat transfer and heat shields. Industries that use aluminum channels include construction, industrial manufacturing, shipping, automotive, aerospace, medical and automotive.
Aluminum Extruded Tubing
Aluminum extruded tubing is a hollow linear aluminum product that is typically cylindrical, however aluminum square tubing and aluminum rectangular tubing is also manufactured for specialty applications such as aluminum downspouts and building supplies. Aluminum tubing may also have rectangular, square or round cross-sections. Formed during extrusion processes, aluminum tubing may be hot extruded, cold extruded or warm extruded, all of which extrude aluminum through a die, although at various temperatures.
The term “aluminum extruders” refers to both the machines and the manufacturers that fabricate aluminum products via the extrusion process. Aluminum extrusion is a popular process because of aluminum’s many attributes, which include flexibility, recyclability, durability, high structural strength and a comparably low weight that makes it cheaper to ship and perfect for use with applications with weight restrictions and sensitivities. In addition, it remains strong in cold temperatures in which other metals would become brittle and break, it is non-toxic and non-magnetic, it conducts electricity and it responds incredibly well to alloying.
Aluminum shapes are linear aluminum products highly valued in a wide spectrum of structural applications due to aluminum's high strength-to-weight ratio and the cost effectiveness of the metal extrusion process. Aluminum is one of the most recent metals to be used in industrial manufacturing processes with just over a hundred years of usage in industrial and commercial applications. However new though, aluminum shapes have a far longer service life than most metal extruded shapes and are therefore embraced. Standard aluminum shapes include beams, trim caps, rods, angles, bars and channels, all of which are available in a wide range of configurations and sizes.
Aluminum extruded tubing is a hollow linear cylindrical, square, round, or rectangular tubing manufactured for uses such as downspouts and building supplies. Tubing can be formed using either hot, cold, or warm extrusion methods. Extruded tubing has a wide variety of applications, which include mining equipment, hardware joints, fluid and gas transport, light building frames, structural applications, lighting fixtures and light poles. As with other extruded products, aluminum tubing is an excellent heat conductor or reflector, is flexible, and has a high strength-to-weight ratio.
Extruded aluminum is an inexpensive and versatile product with possible uses that spread far and wide across the industrial and manufacturing worlds. Extruded aluminum is used the most by the industrial, automotive and construction industries. Shapes like rods, profiles, tubing, channels, trim and angles also contribute to products used in architecture, aerospace, commercial furniture, marine vehicle manufacturing, public transportation, structure, mining, medicine, military and more.
Extruded Aluminum Tubing
Extruded aluminum tubes are extruded products that are used for a variety of applications, especially those where lightweight and corrosion resistance are required. There are two main types of structural aluminum tubing. The first splits the aluminum tube and reseals it under high temperature and pressure conditions. The resealing is also facilitated by metallurgical welds. The seam is also created during this process and in some cases can be seen by the naked eye. Tubes made with this method are not ideal for the transportation of gases or liquids under high pressure because of the possible breakage or leak of the seam.
Fabricated Aluminum Extrusions
Fabricated aluminum extrusions refer to the different forms, shapes and sizes that aluminum can be extruded into. The general process involves heating up a piece of aluminum and passing it through a shaped opening in a die. The emerging aluminum product takes on the shape of the opening in the die and it is then cooled, straightened, and cut. Using a different die opening causes a change in shape of the emerging piece of aluminum. There are several forms of fabricated aluminum extrusions namely: aluminum angles, beams, channels, bars, plates, sheets, pipes, tubes, and gratings.
Structural aluminum goes through post forming treatments to make it light weight, durable, and corrosion resistant for high-strength applications. Since pure aluminum is too soft for structural applications, it has to be alloyed with magnesium, silicon, zinc, copper, zirconium, chromium, or manganese. The most common aluminum alloy is 6061-T6, which is a combination of aluminum, manganese and silicone.
Structural aluminum is more costly to produce but has a faster manufacturing process and low labor costs. Other benefits of structural aluminum are its cleanness and aesthetically pleasing appearance that can be painted or finished. It is commonly used by marine, automotive, engineering and construction industries to produce machine bases, building framing, cryogenic vessels, piping, bridges, and industrial machinery. Regardless of its strength, it can be easily formed into several shapes such as castings, forgings, wire, rod, bar, and flat rolled sheets or plates.
T-Slot Aluminum Extrusion
T-slot aluminum extrusion is a structural fabricated die that utilizes an engineered cross-sectional profile that is both strong and versatile. Aluminum extrusion in itself is a technique used to transform aluminum alloy into objects with a definitive cross-sectional profile for a wide range of uses. A t-shaped extrusion process makes most of the aluminum’s unique combination of physical characteristics. The malleability allows it to be easily machined and cast. Using aluminum allows for one third the density and stiffness of steel so the resulting products offer strength and stability, particularly when alloyed with other metals.
Aluminum trim is long, thin, narrow extrusions used for automotive designs, decorative architecture, screen printing, indoor and outdoor lighting, and construction and engineering projects. It is weather resistant, impervious to high and low temperatures, and corrosion and rust resistant.
Trim manufacturers use all three of the different fabrication methods. Over the past few years, aluminum trim has found wide use in the automotive industry due to its light weight, which helps to lower the overall weight of vehicles to increase gas mileage. Most of the vehicles produced since 2012 have used aluminum trim for interior and exterior accents, instead of heavier, more expensive metals like steel and chrome.
In addition to being lightweight and inexpensive, aluminum trim is flexible and can be extruded in a variety of shapes, have finishes applied, and holds its shine. Interior trim for vehicles is small with detailed surface patterns or textures. With the help of the right finish, aluminum trim can look luxurious while saving manufacturers production costs.
In architecture, aluminum trim is used most often to create exterior accents on both residential and commercial buildings. Trim used in buildings as an aesthetic accent has a secondary processing of powder coating to provide extra water and corrosion resistance. Possible defects in aluminum trim include surface cracking, internal cracking, surface lines, and pipe, which can be prevented during the die design phase.
Aluminum profiles are the shape of extruded aluminum products and include trim caps, rods, angles, bars, and channels, which is a small portion of the wide range of configurations and sizes that aluminum profiles can take. Profiles can be hot, cold, or warm extruded through a die that has the shape of the profile. There are standard profile designs that are generally used, or profiles can be custom designed for special applications. The most common alloys used in the fabrication of profiles are 6061, 6063 and 1100 aluminums.
The profile plays a critical part in the extrusion process. The billet or log forced through the die emerges in a shape, which is referred to as the profile. The design of the profile is created during the design phase where its dimensions and shape are determined. Over the many years that extrusion has been used, a wide range of profiles have been developed that are either hollow, solid, or semi-hollow.
Prior to production, the profile is carefully selected to fit its application. Its shape is forged into the die to precisely match its design requirements. Once the profile is approved and the die cast, it is applied to the application process and the product or part is produced.
A heatsink is a metallic device that absorbs thermal energy, or heat, from another object using thermal compounds known as thermally conductive materials. Heat is absorbed from the object at a relatively high temperature and transferred to the heatsink, which has a larger heat capacity. Extruded heatsinks are a thermal energy solution for both low and high volumes and are used in refrigeration, heat engines, cooling medical devices, lasers, and CPUs.
Heatsink applications are used by production processes that require efficient heat dissipation such as the electronic, military, medical equipment, industrial manufacturing, appliance, and LED lighting industries. Extruded heatsinks vary in design by length, noise level, speed, width, style, height, and weight. Other forms of heatsinks, that are not extruded, are stamped, bonded, or folded, which have higher production costs.
Extruded heatsinks are made from aluminum alloys 6061 and 6063. The most common design is a flat aluminum base with vertical radiating fins to increase surface area. Three things are required for the transfer of thermal energy: a heat source, a thermal compound, and a heatsink. Heat sources must have a high temperature and be thermally bonded to the base of the heatsink by a thermal compound for the heat transfer to occur. Thermal compounds are a paste-like substance made of particles of silver, which has a very low thermal resistance. Once bonded, heat transfer brings the heat source into thermal equilibrium as the heatsink lowers its temperature.
Extruded heat sinks can be passive or active. Active heat sinks use a power source such as integrated fans with directed fins that direct airflow patterns in order to help to increase the surface area of the heatsink. Passive heatsinks do not use any mechanical components. Heat is dissipated through convection or transfer of heat through a liquid or gas caused by molecular motion.
Heatsinks are a major part of the computer age and the most important component for computer efficiency. Computer processors are capable of completing multiple operations rapidly, which generates a great deal of heat. To control the heat, a heatsink transfers keeping the computer from overheating. Without the dispersal of heat by a heatsink, computers would shut down causing thousands of dollars of damage. Every computing device has some form of heatsink for protection and optimal performance.