Extrusion press 1600
Production of aluminum profiles by extrusion method:
Extrusion is generally a process in which aluminum billets, under pressure, pass through a mold with a specific shape and produce a cross-sectional area. Extrusion has different methods, the most common and simplest form is direct extrusion. The container of the device is made of several layers of steel (usually two layers) and is usually able to withstand very high radial stresses. To produce aluminum profiles, aluminum billets that have already reached the appropriate production temperature in the preheating furnace are placed inside the machine.
The trap is then placed behind the billet and the mandrel presses on the billet by means of powerful hydraulic cylinders. Due to the applied pressure, the temperature rises and semi-molten and paste-like materials pass through the mold and form the shape of the profile. The presence of frictional forces significantly increases the pressure of the press.
It has been experimentally observed that in the first phase of production, when the billet is placed behind the mold, the pressure of the machine increases rapidly to its maximum value and the production status of the profile is unstable. To correct and determine the problems of the mold, they use the protruding branch of the mold, which expresses the problems in production. The extruded profile that comes out of the mold must be pulled out manually or automatically. This greatly reduces the pressure and helps to produce the desired profile. The puller machine pulls out the profile with one hand and with equal force and places it on the rails in front of the machine. This greatly helps to twist and modify the complexity of the profile. In the second phase of billet production, it will reach a stable state and the pressure on the machine will be reduced, and the profile will be of good quality. In the third phase, the billet is gradually completed, the pressure on the device reaches its minimum.
After finishing one billet, the next billets are placed in the machine in a row. In this way, profiles of infinite length can be produced. After production, the extruded profiles can be cut to the desired dimensions with a saw. Usually in the production process, 6 to 8% of the length of the billet is the end area that is not used in the process and is called the bottom of the billet. Temperature is a very important element in the production process of extrusion profiles. As the temperature rises, the stress of the material decreases and extrusion becomes easier, but the temperature may also reach the melting point of the alloy, which causes the loss of the desired properties for the alloys used in production. Increasing the speed of the ROM increases the pressure and consequently raises its temperature.
At lower ROM speeds, the heat generated for the transfer is lower as well as the profile production speed is lower. To reduce production waste, temperature, pressure and speed must be controlled at all stages of production. The complexity of the relationships between these three variables has caused the tolerance of the stiffness of the produced profiles to be different.
Extrusion is an aluminum deformation process in which an aluminum metal block (billet) passes through a mold with a smaller cross section due to pressure. Extrusion is in fact an indirect compaction process. The forces required for this compaction are generated by the contact of the billet with the mold chamber and the mold, the amounts of which are very large. Contact of the billet with the mold and mold chamber leads to high compressive stresses which reduce the possibility of surface cracking of the billet during the process. Aluminum extrusion is the best way to break the casting structure of the aluminum billet because in this process the billet only It is affected by compressive forces. Depending on the type of alloy and the desired method, extrusion can be done hot or cold.
In hot extrusion, the billet is preheated to facilitate plastic deformation.
In direct extrusion, which is the most common method used in aluminum extrusion, the billet is placed inside the mold chamber and pushed into the mold with a smooth pressure. The direct extrusion method is used in the production of aluminum rebar, aluminum wire, aluminum pipe and hollow and hollow aluminum sections.
In direct extrusion, the metal flow is in the same direction as the smooth motion. The billet slides on the wall of the mold chamber during the process.
The presence of frictional forces significantly increases the pressure required by the ROM. Once the extrusion is complete, surface treatment is usually necessary to improve corrosion and oxidation resistance. The animation video of how to perform aluminum extrusion operations and production of aluminum profiles can be seen below.
Making an aluminum extrusion mold involves many steps and processes. The construction of the mold starts from the delivery of the desired cross-sectional map and ends with the delivery of the mold to the customer. Two separate issues must be considered in the construction of the mold.
The first issue is that the manufacture of extrusion molds should be done on the basis of economic principles and extrusion efficiency. The second issue is that the design of the extrusion mold should create high quality in the product. New technology allows mold manufacturers to reduce the number of manufacturing steps to some extent and always have a higher quality mold.
The output of the produced extrusion is due to being equipped with an automatic table, which prevents the aluminum profile from abrasion during the extrusion operation by the press table, so that after the operation, we will see a completely smooth and uniform surface on the produced profile.
Steps of fabrication of aluminum extrusion mold after approval of profile cross-sectional map includes a set of which in order:
1: Design with the help of software
2: Cutting steel
3: Turning
4: Machining using CNC
5: Hard work
6: Wirecut
7: Spark
8: Tension
9: Masonry
10: Fillering and finally the final preparation and payment on the mold for production.
Akpa Iran Production Group is ready to consult and provide services until the final production for the extrusion operation of aluminum profiles for any type of application with different levels.
Direct and indirect extrusion
There are two types of extrusion processes, direct and indirect
Direct extrusion is a process in which the mold is held stationary at the tip of the machine and the ROM is movable, applying force to the ingot.
Indirect extrusion is the process in which the billet is stationary while the mold assembly is in the ROM and flows in the mold as the ROM moves against the metal billet.
Hardening: It is a complex combination of heat and mechanical operation.
Factors influencing extrusion operation: The size and shape of the mold is one of the determining factors, pressure, speed, billet temperature during operation, alloy quality, tolerance required and other factors.
In general, the extrusion speed is directly related to the ingot temperature and the amount of pressure inside the container. The temperature and pressure in turn depend on the alloy material and the shape of the mold.
For example: Low temperature extrusion is usually used to produce high quality surface profiles and ultra-precise sizes (usually used in the aerospace industry). This type of extrusion requires a lot of pressure. Sometimes it is impossible to extrude certain profiles due to pressure limitations.
Ingot reference temperature: is the temperature that provides an acceptable level and tolerance.
It is better to extrude the ingots at low temperatures, and of course there are exceptions for some aluminum ingots that preheat to 498-526 ° C.
At extremely high temperatures, the extrusion speed will be high, and as a result, the metal will flow like a fluid stream, which causes the metal to pass through the least resistive ducts, thus filling large ducts inside the mold and ducts. They stay small and tight.
Under these conditions, the size and tolerance of the production profiles are lower than acceptable (standard) and this defect is especially visible in the thin parts and curvatures of the production profiles.
Another result of extrusion at high temperatures and high speeds is the rupture of thin metal edges and sharp corners. It also reduces the tensile strength of the metal. High speed and temperature cause defects and unevenness during production on the metal surface with forward rollers and cause a strong tendency in the production profiles to deform in a wavy manner (warping).
One of the important rules in the high mechanical quality of an alloy is that the extrusion coefficient is low, high friction between the billet and the container prolongs the extrusion time.
Extrusion coefficient: A mold represents the amount of mechanical work that occurs when the profile is extruded.
When the extrusion coefficient is one part less, that part of the profile is faced with an increase in the mass of the metal and the quality of the mechanical work it will perform decreases.
The ability of products with high extrusion coefficients is observed when high pressure is required in small and delicate molds and also when hard mechanical work will occur.
Another important factor that plays an important role in the extrusion of the part or profile is the extrusion factor.
The first extrusion process involved lead pipes in the early nineteenth century. Extrusion is a process in which the cross section of the billet is reduced by passing it through a mold with a special shape. The main goal of this process is to obtain the desired product with desirable mechanical and metallurgical properties without defects. Extrusion is generally used to produce irregular cross-sectional shapes.
However, cylindrical rods or hollow tubes made of soft metals can be deformed using this process. Extrusion of metals and alloys such as aluminum, zinc, steel and nickel-based alloys is possible today. The following figure shows the process of metal extrusion schematically.
This process can also be divided into cold extrusion and hot extrusion in terms of temperature.
Cold extrusion has many advantages over other fabrication methods used in industrial applications. Including:
• The least amount of material waste
• High dimensional accuracy
• Reduce or eliminate the need for machining completely
• Good polishing level and better mechanical properties of the product than the raw material.
Cold extrusion
Cold extrusion is a type of cold forming process in which a raw material in the form of rods, wires is used to produce small parts such as car spark plugs, axles, cans and hollow cylinders, etc. In fact, the parts that have axial symmetry, dimensional accuracy and good surface finish, the most suitable and inexpensive method to produce them, is extrusion.
In cold extrusion, due to the high deformation resistance, there is a limit to the use of hard alloys. Occasionally, to increase the efficiency of the cold extrusion process, pre-pressing operations at temperatures below 400 ° C and the use of lubricants have been suggested. Today, the use of this process in the production of auto parts, military equipment, industrial machinery and electronic equipment is common (the schematic of the mold is shown in Figure 3 for cold extrusion).
This process is used to produce semi-finished metal products with almost long length and fixed cross section such as solid and hollow profiles, symmetrical and asymmetric aluminum, copper, steel and their alloys. One of the main reasons for using hot extrusion process is to reduce the material silane stress due to stiffness. In fact, by heating the primary ingot, the problem of achieving very high pressures is solved.
A noteworthy point in hot extrusion is the problems caused by heating the metal. These issues include:
Oxidation of ingots and work tools
• Softening tools and molds
• Lubrication problem
cited. For this purpose, it is always tried that the metal has a suitable plastic deformation up to the minimum temperature; Be heated. It is caused by the large deformation caused by that piece. Therefore, the working temperature in hot extrusion must be selected in such a way that the part does not reach the frying range or even the melting point during deformation.
In hot extrusion of steels, the ingots are heated in the temperature range of 1100 to 1200 degrees Celsius and to prevent heat shocks, the tool is kept in the temperature range of 350 degrees Celsius. The extrusion pressure range for steels is 870 to 1260 MPa. (Schematic of the mold is shown in Figure 4 for hot extrusion).
The extrusion industry has a history of over 150 years. The first process is a 1870 report by Joseph Brahmah. The report described Percy pumping molten lead into a cylindrical mold. In 1820, Thomas Bohr built hydraulic presses to produce pipes and used them to make lead cylinders. Cold extrusion of steel first began in Europe in the mid-1930s, and some military leaf instruments such as bullet casings, etc. were made of steel.
At the same time, the Germans were conducting research on cold steel extrusion, which was not published until 1924 due to military secrecy. After World War II, the US military was able to make cold shells and 75 mm bullets by cold extrusion.
In cold extrusion, there is no need to heat the raw materials before starting work and this operation is done at or near room temperature.
Among the advantages of cold extrusion compared to hot extrusion, reduction of surface oxidation, obtaining high strength due to cold work, quality finished surface and so on. Lubrication in extrusion and cold forging is similar to lubrication when the pipe is cold drawn, but due to the high surface area during the extrusion operation, the lubrication must be much more intense. Conversion coatings are required for this operation, unless hydrostatic lubrication is used. The only other way is to cover the metal surface with tin or silver.
Adhesion and scaling are the biggest limitations of cold extrusion, but the important issue is to reduce the forces as much as possible. Because very high stresses occur in cold extrusion. However, in this case, as in deepening, flow and rupture can be controlled through lubrication at certain levels. This is especially important for filling out the template correctly.
In hot extrusion, the material is heated before extrusion. The amount of heating varies in different materials. Hot extrusion is in dire need of lubrication. Among the materials used for lubrication in hot extrusion are:
• Graphite
• Glass
• Inorganic salts
In this case, graphite is very effective, even at high temperatures, because contact with air is practically low and therefore oxidation of graphite is not significant.
Extrusion of long parts is possible if the lubricant is made into a plate that gently softens or melts during work and forms a thin coating on the surface of the part as the metal passes through the mold. Glass is the most used material as the material from which the plate is made. However, a variety of inorganic salts that have a good melting point can also be used in this case.
Most glass lubricating extrusions are done using flat molds (180 degrees), but if conical molds (150-120 degrees) are used, less force is required and the metal and glass flow better. Cone molds also reduce the possibility of subsurface defects, but are not industrially desirable because of the high amount of residual or waste metal in them, unless a disposable metal piece is placed behind the ingot as a backing.
One of the most important sub-issues in extrusion is the avoidance of oxidation during heating in the furnace or during the transfer of the torch to the extrusion press. In this case, glass coatings or other protective coatings can be used. But torches are usually heated in a furnace with a controlled environment.
Aluminum is often heated to 550-500 ° C without lubrication in extrusion flat molds. The reason for non-lubrication is to avoid the interactions of oxide and lubricant materials that cause surface and subsurface defects. If conical molds are used, oil or graphite can be used for lubrication. Deformation forces are reduced if these materials are used, but stains may occur on the parts. Graphite can be easily seen on a shiny piece of aluminum. Cone molds also produce larger waste pieces. Adhesion and scaling can be a major problem, and this is especially important for complex extruded parts such as glazed rods that are later plated. After this operation, all shells and bumps are identified.
