About Aluminum Extrusion
Aluminum Extrusion is a key method for forming aluminum, involving high pressure to mould Aluminum billets into desired shapes. In this process, the billet is placed into an extrusion cylinder and pressure is applied, pushing the material through an opening to form it. This technique, based on principles of Aluminum plastic forming, efficiently produces tubes, rods, and various profiles like T-shapes and L-shapes in one go. It is versatile and suitable for non-ferrous Aluminum, steel, and alloys of aluminum, copper, and magnesium. The extrusion process can be divided into hot extrusion and cold extrusion.
Advantages of Aluminum Extrusion
- High extrusion ratio (i.e., the ratio of the aluminum cross-sectional area to the extruded part cross-sectional area).
- It can easily create complex cross-sections.
- This processing can be completed using brittle materials and ductile materials.
- High mechanical performance is achievable through cold extrusion.
Disadvantages of Aluminum Extrusion
- High initial or setup costs.
- Requires high compressive force.
Comparison of Cold and Hot Aluminum Extrusion
Cold Aluminum Extrusion: Cold extrusion is performed at room temperature by placing the Aluminum blank in the cold extrusion die cavity and applying pressure through the punch on the press, causing the aluminum blank to undergo plastic deformation, thereby machining parts. This method does not require heating the aluminum, thus it is suitable for parts production that requires higher material strength. Cold extrusion can be applied to various aluminum, including lead, tin, aluminum, copper, zinc, and their alloys. It features precise dimensions, material savings, high production efficiency, and wide applicability.
Hot Aluminum Extrusion: This is performed by extruding Aluminum heated below its recrystallization temperature. This method also belongs to the machining processes of parts with little to no cutting. Hot extrusion is suitable for materials with poor plasticity in their cold state; heating can improve the material’s plasticity, facilitating forming. Compared to cold extrusion, hot extrusion is more suitable for producing large or complex-shaped parts. However, the disadvantages of hot extrusion include higher energy consumption and the need for additional heating equipment, which increases production costs.
At Conco Machining, we leverage our decades of expertise to offer both hot and cold extrusion services for aluminum. Our facilities are equipped to handle a diverse range of aluminum types and sizes, from 7075 to 6063, catering to custom and complex project requirements. Visit “Custom Aluminum Extrusion Services” to explore the possibilities
Features of Hot and Cold Aluminum Extrusion
Hot Aluminum Extrusion
Definition: It involves various extrusion shaping of Aluminums at forging temperatures, taking advantage of the good plasticity of the materials. Hot extrusion is mainly used for manufacturing ordinary cross-sectional long pieces, profiles, tubes, rods, and various machine parts. Hot extrusion can not only form non-ferrous Aluminum and its alloys, which are good in plasticity and relatively lower in strength, such as low and medium carbon steels, but it can also form high-strength high-carbon, high-alloy steels, such as structural special, stainless steels, high-speed tool steels, and heat-resistant steels. Generally, machine parts after hot extrusion forming are further machined to improve the dimensional accuracy and surface quality.
Process Characteristics:
- High-temperature operation: The Aluminum billet is extruded at high temperatures, typically above the Aluminum’s recrystallization temperature. For example, the hot extrusion temperature for aluminum is about 450°C to 500°C, while for steel, it is between 1000°C and 1200°C.
- Low flow stress: High temperatures significantly reduce the Aluminum’s flow stress, making deformation easier during the extrusion process.
- Reduced hardening effect: Extrusion at high temperatures reduces the hardening effect of Aluminums, making subsequent processing easier.
- Complex shapes and large sizes: Hot extrusion is suitable for producing complex shapes and large-sized products as Aluminums has better plasticity at high temperatures.
Cold Aluminum Extrusion
Definition: Aluminum Extrusion is a process that forces Aluminum chips to flow plastically through the gap between the punch and the die or the die outlet to manufacture hollow or sectionally smaller parts than the blank. If the blank is extruded without heating, it is called cold extrusion. Cold extrusion is one of the chip-less or minimal chip part machining processes, thus it is an advanced method in chip plastic processing. Therefore, it is suitable for smaller and medium-sized products.
Process Characteristics:
- Room temperature or slightly higher operation: Aluminum billet is extruded at room temperature or just above room temperature.
- High flow stress: As the Aluminum is extruded at lower temperatures, the flow stress is higher, requiring the extrusion machine to have a greater pressure capability.
- Higher surface quality: Cold-extruded products generally have higher surface smoothness and dimensional accuracy.
- Significant hardening effect: The aluminum undergoes significant hardening during the cold extrusion process, which may require subsequent heat treatment to relieve stress.
- Drawing is a similar process that uses the material’s tensile strength to pull it through a die. It limits the amount of change that can be made in one step, therefore it is only suitable for simpler shapes and usually requires multiple stages. Wire drawing is the main method of producing wire. Aluminum rods and tubes are also often drawn.
- Extrusion can be continuous (theoretically can produce infinitely long materials) or semi-continuous (producing many pieces). It can be done with hot or cold materials. Common extrusion materials include aluminum, polymers, ceramics, concrete, modelling clay, and food.
- Extruded products are generally called extrusions. Also known as “hole flanging”, the cavities in extruded materials cannot be produced with simple flat extrusion dies because there is no way to support the centre barrier of the mould. Instead, the mould adopts a block shape with depth, starting from the shape profile supporting the centre part first. Then the mould shape changes internally along its length to the final shape, with the hanging centrepiece supported by the back of the mould. The material flows around the support and merges to form the desired closed shape. Aluminum extrusion can also increase its strength.
Aluminum Extrusion Process Steps
Preparing the Aluminum Billet: Select the appropriate aluminum billet, usually cylindrical or square blocks of aluminum. Subsequently, the billets are heated as required by their length dimensions. Hot extrusion is generally performed above the crystallization temperature to reduce the aluminum’s strength and improve its plasticity. Cold extrusion, on the other hand, is carried out at room temperature or slightly higher temperatures. The billet for aluminum alloys is a solid cylindrical block. After being taken from longer alloy sections, it is preheated in an oven at 400-500 degrees Celsius, thus providing the right level of ductility for the extrusion process.
Loading into the Aluminum Extrusion Press: After the Aluminum billet is preheated, it is mechanically moved to the extrusion press. Lubricants (release agents) are applied to the billet and the slider to prevent them from sticking together. Then, the billet is loaded into the press.
Applying Pressure: When the extrusion press is loaded with the forgeable Aluminum billet, the hydraulic ram applies a pressure of up to 15,000 tons. As the punch applies pressure, the billet is pushed into the container of the extrusion press. Finally, the material expands significantly, filling the walls of the container. The extrusion press applies high pressure through hydraulic or mechanical devices, pushing the billet towards the die opening, and ultimately forming a specific cross-sectional shape.
Cooling and Cutting: After the aluminum profile is extruded, it is cooled and then cut to the required length. Depending on the product requirements, further processing or treatment may be needed, such as heat treatment, surface treatment, or mechanical processing.
Industry Application: Custome Aluminum Extrusion service at Conco Machining.
Types of Aluminum Extrusion
1. Direct Aluminum Extrusion
Direct extrusion, sometimes called forward extrusion, is the most common type of extrusion. First, the heated Aluminum billet (only used for hot extrusion, discussed later) is loaded into the die cavity container, with a dummy block placed behind it. Then a mechanical or hydraulic plunger presses on the material, pushing it out of the mould. Then, while still hot, the parts are stretched to straighten them.
In direct extrusion, molten glass is used as a lubricant to reduce the high friction caused by steel at higher temperatures, while graphite powder oil is used for low-temperature lubrication. The dummy block is used to protect the tip of the ram (punch or plunger) during hot extrusion. When the punch reaches the end of its stroke, a small part of the billet, known as the “butt end,” cannot pass through the mould opening.
Advantages of Direct Aluminum Extrusion
- No need to modify the aluminum
- Can be used for both hot and cold extrusion
- Simpler processing compared to other extrusion processes
Disadvantages of Direct Aluminum Extrusion
- High friction requirements
- The tail end remains in the cavity
- The force required to push the plunger varies as the punch moves
1. Indirect Aluminum Extrusion
Also known as reverse extrusion or backward extrusion, this is a aluminum forming process. In this process, the die and the Aluminum billet move relative to each other, with the aluminum billet fixed in place, and the die moving towards the billet direction, forcing the aluminum through the die opening. This method reduces the friction between the billet and the extrusion cylinder walls, thereby lowering the extrusion force and enhancing the material’s flow.
Advantages of Indirect Aluminum Extrusion
- Less friction and lower electricity consumption
- Can be used for both hot and cold extrusion
- Simpler processing compared to other extrusion processes
Disadvantages of Indirect Aluminum Extrusion
- Difficult to support the extrusion parts
- Hollow plungers limit the load applied
3. Hydrostatic Aluminum Extrusion
Hydrostatic extrusion is a special aluminum extrusion process where aluminum billets are extruded by applying uniform hydrostatic pressure in a liquid medium. This process has unique advantages in certain applications, particularly when dealing with high-strength materials and manufacturing high-precision parts. In hydrostatic extrusion, the chamber/die cavity is smaller than the billet and filled with hydraulic oil, which transfers the force from the plunger to the billet. Although the fluid applies triaxial forces, the pressure enhances the billet’s formability. Sealing the fluid early in the process is essential to prevent any leakage and decompression issues.
Advantages of Hydrostatic Aluminum Extrusion
- Low power/force requirements due to no friction
- Fast production speed and high reduction ratio
- Reduced Aluminum billet temperatureUniform material flow due to balanced force distribution
- Capable of extruding large Aluminum billets and large sections
- No Aluminum billet residue inside the container
Disadvantages of Hydrostatic Aluminum Extrusion
- The Aluminum billet needs to be prepared by tapering one end to match the die entry angle
- Only cold extrusion is possible
- Difficult to accommodate high-pressure fluids
4. Lateral Aluminum Extrusion
Definition: Lateral extrusion, also known as transverse extrusion, is a aluminum forming process where the direction of material flow is perpendicular to the direction of applied force. This unique setup allows the production of parts with complex lateral shapes that are difficult to achieve through traditional longitudinal extrusion methods.
Process Description: In lateral extrusion, the aluminum billet is placed in a die that is designed to apply pressure from the side rather than the end. As pressure is applied laterally, the aluminum flows through a specifically designed opening on the opposite side of the pressure application. This method is particularly useful for creating objects with intricate cross-sections and features extending outward from the original billet’s central axis.
Applications:
- Manufacturing of Gears: Lateral extrusion is often used to produce gears with intricate tooth profiles directly from the Aluminum billet, reducing the need for further machining.
- Production of Complex Brackets: This technique can be used to manufacture brackets with specific lateral profiles that may be required for aerospace and automotive applications.
- Tool and Die Components: Lateral extrusion can produce complex tool shapes for industrial manufacturing processes.
Advantages:
- Complex Shapes: Allows the formation of complex lateral shapes not possible with standard extrusion techniques.
- Reduced Machining: Parts produced through lateral extrusion often require less secondary machining, saving time and resources.
- Improved Material Properties: The process can enhance material properties through work hardening induced by the deformation process.
Disadvantages:
- Limited Material Choices: Not all materials are suitable for lateral extrusion due to their lack of ductility when subjected to lateral forces.
- Complex Die Design: The dies required for lateral extrusion are complex and can be costly to design and manufacture.
- Specialized Equipment Needed: Requires specific presses capable of applying forces in non-traditional directions, which can increase setup costs.
5. Impact Aluminum Extrusion
Impact extrusion is part of the cold extrusion category and is very similar to indirect extrusion, but limited to softer aluminums like lead, aluminum, and copper. The thickness of the extruded product is a function of the gap between the punch and the die cavity. An ejector plate is used to slide the extrusion off the punch.
Types of Aluminum Extrusion
Direct Impact Extrusion: In direct impact extrusion, the aluminum billet is subjected to high-speed impact within the die, directly extruding from the die’s outlet. This method is suitable for materials with good flow properties, such as aluminum, lead, zinc, etc., capable of quickly and efficiently producing complex-shaped products.
Reverse Impact Extrusion: Reverse impact extrusion works the opposite way of direct impact extrusion. The aluminum billet enters from the bottom of the die, and by applying pressure, it is extruded and released from the top outlet. This method is typically suitable for more viscous aluminum materials like copper, nickel, etc.
Combined Aluminum Extrusion: Combined impact extrusion combines the advantages of both forward and reverse methods by applying pressure in multiple directions within the die, allowing for more complex shapes and more precise size control. This method can adapt to different materials with varying flow and deformation properties, making the production process more flexible and efficient.
Advantages of Impact Aluminum Extrusion
- Saves up to 90% of raw materials
- Reduces processing time by up to 75%
- Eliminates secondary processing operations
- Reduces multi-part assembly
- Due to the cold working of materials, it enhances the mechanical properties and machinability of materials
- Significantly reduces the total part cost by up to 50%
- One-end closed hollow thin-walled tubes are typically produced in the industry by reverse impact extrusion.
Disadvantages of Impact Aluminum Extrusion
- Production is possible only as long as the part is symmetrical along its axis of formation.
- Many parts formed industrially by impact require further manufacturing processes before completion, such as aluminum forging, ironing, or machining.
Conclusion
Aluminum extrusion is an efficient, flexible, and widely applicable aluminum forming process, suitable for a variety of materials and complex-shaped product production. By selecting the appropriate type of extrusion and process parameters, production efficiency and product quality can be effectively enhanced to meet the demands of different industries. High-quality, complex-shaped aluminum profiles can be produced.
