Actually, the aluminum alloy extrusion process begins with product design because product design based on the given usage requirements which determine the final parameters of the products, such as the mechanical processing performance of the product, surface treatment performance and the use of environmental requirements which have determined the choice of extruded aluminum alloy type. With the same aluminum alloy, the performance of the extruded aluminum profile depends on the design shape of the product which determines the shape of the extrusion die. Once the design problem is solved, the actual extrusion process begins with the extrusion of aluminum cast rod. Aluminum cast rod must be heated to soften before extrusion and put the heated rod into the ingot cylinder of the extruder, then the high-power hydraulic cylinder pushes the extrusion bar which has extrusion pad in the front so that the heated and softened aluminum alloy will be extruded from the precision molding hole of the die under the strong pressure of the extrusion pad. This is the role of the mold: to produce the shape of the desired product.
(This picture is a schematic diagram of a typical horizontal hydraulic extruder, and the extrusion direction is from left to right)
This is a simple description on direct extrusion which is the most widely used. Indirect extrusion is a similar process, but with some differences. In the direct extrusion process, the die is not moving, and the pressure of the extrusion bar pushes the aluminum alloy through the die hole. While in the indirect extrusion process, the die is mounted on the hollow extrusion bar, so that the die is extruded to the motionless aluminum bar blank, forcing the aluminum alloy through the die to the hollow extrusion bar.
In fact, the extrusion process is similar to squeezing toothpaste. When the pressure is applied to the closed end of the toothpaste, the cylindrical toothpaste is squeezed out of the round opening. If the opening is flat, the toothpaste is squeezed out of the ribbon. Of course, complex shapes can be squeezed out of openings of the same shape as well. For example, cake makers make all kinds of decorative edges by using specially shaped tubes to squeeze ice cream. What they do is extrusion forming. Even though you can't make products out of toothpaste or ice cream, or squeeze aluminum alloy into aluminum tubes with your fingers but relying on a high-powered hydraulic press to squeeze aluminum alloy out of a certain shape of die hole to produce a wide variety of useful products of almost any shape.
(Below (left) the first profile has just been extruded at the beginning of extrusion, and (right) the aluminum profile is in the production process.)
Aluminium rod
Aluminum rod is the blank in the extrusion process, no matter solid or hollow, is usually a cylinder in usual which length is determined by the extrusion ingot cylinder. Generally, aluminum rods are molded by casting, but also by forging or powder forging, by adjusting the alloy composition of the aluminum alloy bar saw cut. Furthermore, aluminum alloys are composed of more than one metal element (usually no more than 5%) elements (such as copper, magnesium, silicon, manganese or zinc) that enhance the properties of pure aluminum and affect the extrusion process.
The length of the aluminum bar from each manufacturer is not consistent, which is determined by the final length of the aluminum profile, the extrusion ratio, the discharge length and the extrusion allowance. Standard lengths generally range from 26 inches (660mm) to 72 inches (1,830 mm), and outside diameters range from 3 inches (76mm) to 33 inches (838mm), and 6 inches (155mm) to 9 inches (228mm).
Direct extrusion production process
Billet-- heating furnace-- extrusion press with die-- saw-- straighten-- aging oven
(This diagram illustrates the basic steps of extruding an aluminum profile)
When the shape of the final product has been confirmed, the appropriate aluminum alloy has been selected, and the manufacturing of the extrusion die has been completed, the actual extrusion process is started and the preparation is complete. The aluminum rod and the extrusion tool are then preheated. During the extrusion process, the aluminum rod is originally solid, but has become soft in the heating furnace. The melting point of aluminum alloy is about 660°C. The typical heating temperature for the extrusion process is generally greater than 375°C and can be as high as 500°C depending on the extrusion condition of the metal.
The actual extrusion process begins when the extrusion bar begins to apply pressure to the aluminum bar inside the ingot. Different hydraulic presses are designed to squeeze from 100 tons to 15,000 tons, almost any pressure. This extrusion force determines the size of the extruded product produced by the extrusion machine. Extruded product specifications are expressed by the maximum cross-sectional size of the product, sometimes referring to the diameter of the outer circle of the product.
When extrusion has just begun, aluminum rods affected by the reaction of the mold change is short and thick until the expansion of the aluminum rods are constrained by the container ingot tube wall, and then, when the pressure continues to increase, the soft (still) solid metal have no place to flow, start from the mould forming hole squeezed out to the other end of the mould, this creates a profile.
Approximately 10% of the aluminum rod (including the skin of the rod) is left in the ingot drum, the extrusion product is cut from the mold, and the metal remaining in the ingot drum is cleaned and recycled. After the product leaves the die, the hot extruded product is quenched, mechanically treated and aged.
When heated aluminum is extruded from the mold through the ingot cylinder, the metal flows faster in the center of the bar than at the edges. As the black band in the inset shows, the metal at the edges is left behind as a remnant to be recycled.
Extrusion speed depends on the alloy being extruded and the shape of the die hole. Extruding complex shaped materials with hard alloys can be as slow as 1-2 feet per minute while extruding simple materials with soft alloys can reach 180 feet per minute, or even faster.
The length of extrusion product depends on the rod and die outlet hole, and a single continuous extrusion can extrude up to 200 feet of product. In the latest molding extrusion, when the extruded product leaves the extrusion machine, it is placed on the sliding out (equivalent to the conveyor belt). According to the different alloy, the cooling way of the extruded product is divided into natural cooling, air or water cooling quenching. This is a critical step in ensuring the metal properties of the product after aging. The extruded product is then transferred to a cold bed.
Straighten
After the extruded product is quenched (cooled), it is turn to straighten and correct with a stretcher or straightener (stretching is also classified as cold work after extrusion). Finally, the conveying device will send the product to the saw cutting machine.
Sawing
A typical finished sawing is the sawing of a product to a specific commercial length. Nowadays, the circular saw is the most widely used as the spiral arm saw machine will vertically extruded out of the long material saw. There are also saws that cut from the top of the profile (such as electric miter saws). Also, there is a saw table which is a disk saw blade rising from the bottom to cut the product, and then saw blade back to the bottom of the table for the next cycle.
A typical finished circular saw is 16 to 20 inches in diameter and has more than 100 carbide teeth. Large size saw blades are used for large diameter extruder.
Self-lubricating saws are equipped with a system that delivers lubricant to the saws to ensure optimal sawing efficiency and saw surface.
The automatic pressing device holds the profile in place for sawing, and the sawing debris is collected for recycling.
Aging
Some extruded products need to be aged to achieve optimum strength, which called age hardening. Natural aging is done at a room temperature while manual aging is carried out in the aging furnace. Academically, it is called precipitation - enhanced phase heat treatment.
When the profile is extruded from the extruder, the profile becomes semi-solid. But it becomes a solid quickly when cooled or quenched (whether air or water cooled). Non-heat-treated strengthened aluminum alloys (such as those with magnesium or manganese) are strengthened by natural aging and cold working. Heat-treatable strengthened aluminum alloys (such as aluminum alloys with copper, zinc, magnesium and silicon) can obtain better strength and hardness by heat treatment that affects the structure of the aluminum alloy.
In addition, aging is the uniform precipitation of the reinforced phase particles to obtain the maximum yield strength, hardness and elasticity of the special alloy.
Packing
After full aging, either in the furnace or at room temperature, the profiles are transferred to the surface treatment or deep processing workshop to be packed and ready for transportation to customers.
Aluminum profiles can be packed in various ways
The majority of extrusion workshops are packed according to packaging requirements. The profiles should be stacked to prevent surface damage, distortion and other damage. Sometimes, customers have their own packaging requirements. Of course, specific extruded products have specific packaging methods for storage and transportation.
Parts of extrusion unit
Front and rear platens, tie rods and nuts should keep parallel.
The following picture shows an extruder with four tension posts. Extruder can also have only two or three tension posts.
The ram stem is pushed forward by the ram piston/ cylinder and pushed into the container before being extruded into a die (fixed to the tool carrier).
The following labels indicate all the parts of the process
(cross-sections of the die, backer and bolster.)
