Definition of extrusion | types of extrusion, application

Extrusion:

Extrusion is a manufacturing process where a material is pushed or pulled through a die to create a continuous profile or shape with a constant cross-section. This process is commonly used to create products with complex cross-sections and is widely used in the production of plastic and metal parts.

During extrusion, the material is heated and forced through a die, which is a specially designed tool that determines the shape and dimensions of the final product. The material is then cooled as it exits the die, allowing it to maintain its shape and dimensions.

Extrusion principle:

The principle of extrusion involves using a force to push a material through a small opening or orifice to create a uniform shape. The process typically involves a material in a solid or semi-solid state, such as plastic, metal, or food, that is forced through a die or nozzle to produce a continuous shape with a consistent cross-section.

The basic components of an extrusion system include a hopper or container to hold the material, a screw or piston to push the material through the die, and a die or nozzle that shapes the material into the desired form. The material is typically heated to a molten state before it is forced through the die, although some materials can be extruded while in a solid state.

The die or nozzle is a specially designed opening that determines the final shape of the extruded product. The size and shape of the die can be adjusted to produce different shapes and sizes of extruded products.

The extrusion process can be performed using different types of machinery, including single-screw or twin-screw extruders, ram extruders, or screw injection molding machines. The choice of machinery and process parameters will depend on the specific material being extruded and the desired properties of the final product.

Overall, the principle of extrusion allows for the efficient and cost-effective production of a wide range of products with complex shapes and consistent quality. 

Hot extrusion:

Hot extrusion is a manufacturing process that involves the shaping of metal or other materials by forcing them through a die at high temperatures. This process is typically used for materials that are difficult to form at room temperature or that require additional processing steps, such as forging or rolling, to achieve the desired shape.

The hot extrusion process begins with a cylindrical billet, which is heated to a temperature above its recrystallization point. The billet is then loaded into a container that holds a ram, which is used to apply pressure to the material and force it through a die. The die is typically made of steel or carbide and has a shaped opening that defines the final product geometry.

As the billet is forced through the die, it is compressed and deformed to take on the shape of the die opening. The resulting extruded product is continuous and can be cut to the desired length. The process can also be used to create complex shapes with internal cavities or features by using a multi-step die design.

Hot extrusion has several advantages over other manufacturing processes. Because the material is hot and pliable, it can be formed into shapes that are difficult or impossible to achieve using other methods. The process also produces a very dense and uniform product with a fine-grained microstructure, which can result in improved mechanical properties such as strength and toughness.

Working process of hot extrusion 

The hot extrusion process typically involves the following steps:

1. Preparation: The metal billet is heated to a specific temperature that is above its recrystallization temperature but below its melting point. This makes the metal easier to deform without cracking or tearing.

2. Loading: The heated billet is loaded into the extrusion press. The press typically consists of a ram, a container, and a die. The ram pushes the billet into the container, where it is held in place by a dummy block.

3. Extrusion: The ram then pushes the metal through the die, which has a specific shape and size. As the metal passes through the die, it is compressed and forced to take on the shape of the die.

4. Cooling: The extruded part is then cooled and cut to the desired length. The cooling process may involve air cooling or quenching in water or oil, depending on the material being extrusion.

Construction of hot extrusion:

Here are the basic steps involved in hot extrusion:

1. Material Selection: The first step in hot extrusion is to select the appropriate material for the application. Materials that are commonly used for hot extrusion include aluminum, copper, steel, titanium, and nickel alloys.

2. Billet Preparation: The selected material is melted and cast into billets of the desired size and shape. The billets are then heated to the required temperature for the extrusion process. The temperature is typically between 50% and 75% of the material's melting point.

3. Extrusion Machine Setup: The extrusion machine is set up to the desired specifications. This includes selecting the appropriate die and mandrel, and setting the extrusion speed and pressure.

4. Preheating: Before extrusion can begin, the billet is preheated to the same temperature as the extrusion temperature.

5. Extrusion: The preheated billet is then placed into the extrusion machine and forced through the die under high pressure. The die determines the shape and size of the final product.

6. Cooling and Cutting: After the extrusion process, the newly formed product is cooled and cut to the desired length.

7. Post-Extrusion Processing: Additional processing steps, such as heat treatment, machining, or surface finishing, may be performed to achieve the desired final properties and surface finish.

Application of hot extrusion: 

The extrusion process is used to create a variety of metal parts and products, including:

1. Tubes and Pipes: Hot extrusion is commonly used to manufacture seamless tubes and pipes of different sizes and shapes. The process allows for the production of tubes with a high degree of precision, smooth surface finish, and tight tolerances.

2. Automotive Parts: Hot extrusion is used to manufacture various automotive parts such as engine components, suspension parts, and structural parts. The process is ideal for producing parts with complex geometries and high strength-to-weight ratios.

3. Aerospace Parts: Hot extrusion is used to manufacture aerospace parts such as landing gear components, wing spars, and engine components. The process allows for the production of parts with high strength-to-weight ratios and excellent fatigue resistance.

4. Structural Components: Hot extrusion is used to produce a wide range of structural components, including beams, columns, and trusses. The process allows for the production of parts with complex geometries and high strength-to-weight ratios.

5. Electrical Components: Hot extrusion is used to produce electrical components such as wire and cable coatings, bus bars, and connectors. The process allows for the production of parts with excellent conductivity and high strength.

6. Industrial Machinery: Hot extrusion is used to manufacture various industrial machinery components such as gears, bearings, and shafts. The process allows for the production of parts with high precision and strength.

Cold extrusion:

Cold extrusion is a manufacturing process in which a material is formed by applying force to it at room temperature or slightly elevated temperatures. The process involves using a die or a set of dies to shape the material into the desired form.

In cold extrusion, the material is typically a metal or a metal alloy, although other materials such as plastics or ceramics can also be used. The process is often used to create complex shapes that are difficult or impossible to achieve using other manufacturing methods.

The cold extrusion process typically involves the following steps:

1. A material is placed in a die, which is a specialized tool designed to shape the material into the desired form.

2. Pressure is applied to the material using a ram or a press, forcing the material to flow into the die and take on its shape.

3. The extruded material is removed from the die and may undergo additional processing, such as machining or heat treatment, to improve its properties or achieve the desired finish.

4. Cold extrusion has several advantages over other manufacturing methods, including the ability to create complex shapes, high precision, and improved material properties. However, the process can be relatively slow and expensive compared to other methods such as hot extrusion or casting.

Usage of cold extrusion:

Some common applications of cold extrusion include:

1. Automotive industry: Cold extrusion is widely used in the automotive industry to manufacture various parts such as gears, shafts, bearings, and suspension components. These parts are often made from high-strength materials like steel, aluminum, and titanium.

2. Aerospace industry: The aerospace industry also uses cold extrusion to manufacture various parts like fasteners, bolts, and rivets. Cold extrusion is preferred in this industry due to its ability to produce high-strength components with excellent fatigue resistance.

3. Electrical industry: Cold extrusion is used in the electrical industry to manufacture copper and aluminum wires, cables, and connectors. The process is preferred for producing high-quality conductors with excellent electrical conductivity and mechanical strength.

4. Medical industry: Cold extrusion is also used in the medical industry to manufacture various medical devices, such as needles, cannulas, and stents. The process is preferred in this industry due to its ability to produce small, intricate components with high precision.

5. Consumer goods: Cold extrusion is used to manufacture various consumer goods such as kitchen utensils, tools, and sports equipment. The process is preferred in this industry due to its ability to produce components with excellent surface finish and dimensional accuracy.