Extrusion Process: Types, Advantages and Disadvantages

The extrusion process is comparable to drawing, except that drawing extends the metal workpiece using tensile stress. Compared to drawing in one pass, the compressive force allows for significant distortion. Plastic and aluminium are the most widely used materials for extrusion. This article presents all the information you need to understand the extrusion process better. The material that emerges from the die is known as “extrudate”. The metal endures compressive and shear stress to achieve the die shape.

Did You Know? Aluminium extrusion was highly in demand for the production of aircraft and military machinery throughout the two World Wars.

What is the Extrusion Process?

The extrusion process is a manufacturing method that involves pushing a material, often in the form of a plastic or metal, through a die or shape-forming tool. The material is typically heated and then forced through the die by a screw or ram, which shapes it into the desired form. The extrusion process is used to create a wide range of products, including pipes, tubing, cables, sheets, and structural shapes. It is also used in the production of food products such as pasta, cereal, and snacks. 

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How does the Extrusion Process Work?

Extrusion involves the use of compression in the metal-forming process. Under the process, pressure is created, causing a force to be applied to a piece of metal. Following is a process summary to guide you through

1. Preparation of Feed Metal

The billet or ingot is the feed metal used as a raw material in the extrusion process. However, the feed metal must adhere to the designers’ specifications. It usually has a circular or square profile but can also have other shapes. The feed metal is produced using hot rolling or continuous casting techniques.

2. Preparation for Extrusion

The standard raw material is then placed in extrusion equipment, such as a press, and heated to the temperature recommended for the hot extrusion method. Because cold extrusion occurs at room temperature, no preheating is required.

3. Metal Extrusion

The extrusion process is now carried out by applying a compressive force to the material, which pushes it toward the die. There is a small opening in the die. The pressure is released when this process is finished, and the product proceeds to the next step.

4. Heat Treatment and Post-Processing

Heat treatment is now applied to enhance the product’s qualities and prepare it for its intended use. Different metals require different heat treatment procedures. In the case of aluminium, for instance, it first cools the extruded portion before stretching and cutting it to the required lengths. The pieces are then heated to 350 degrees Fahrenheit and left to cool for four hours when they undergo an ageing process to become hardened.

Types of Extrusion

There are several different types of extrusion, each with its own unique characteristics and applications. Some of the most common types include:

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According to the Direction of Flow of Metal

According to the direction of the flow of metal, extrusion can be of three types:

1. Direct Extrusion

Metal is compelled to flow in the direction of the punch feed during this type of extrusion operation. During extrusion, the punch advances toward the die. As a result of the high friction between the billet and the container, this technique demands more force.

2. Indirect Extrusion

Metal flows in the opposite direction of the plunger movement during this process. The die is attached to the side and the punch moves on. Metal flows through the annular gap between the punch and the container in this operation.

3. Hydrostatic Extrusion

In this method, pressure is applied to the billet using fluid. Since the billet is not in contact with either the cylinder wall or the plunger during this procedure, friction is eliminated. Between the billet and the plunger, there is fluid. The force that the plunger applies to the fluid is then transferred to the billet. Vegetable oils are typically used as a fluid. This process was made possible by a leaking issue and an uncontrolled extrusion speed.

According to the Working Temperature

Based on the working temperature, extrusion can be of two types:

1. Hot Extrusion

It is referred to as hot extrusion when extrusion occurs above the recrystallization temperature, which is about 50–60% of its melting point. Compared to extrusion at a cold temperature, hot extrusion requires less force when the metal reaches the recrystallisation temperature. A low surface finish due to scale formation on the extruded part, requiring high maintenance, is always possible.

2. Cold Extrusion

Hot extrusion is a manufacturing process that creates special steel profiles with a constant longitudinal cross-section. It works by using a force known as “compression.” This process can be used in a single step to produce solid or hollow profiled bars with complex geometries and a fixed cross-section.

Applications of Extrusion Process

The extrusion method creates things with predetermined cross-sectional characteristics by forcing material through a die.

• Hollow pipes and tubes are typically made using the extrusion method.
• Aluminium extrusion is used for structural work in a number of industries.
• This process is used in automobile manufacturing to make frames, doors, windows, etc.  

• A common technique for producing plastic goods is extrusion.
• Electrical wires, bars, and tubes can all be produced using the hot extrusion method.
• A few items produced by cold extrusion are cylinders, collapsible cans, gear blanks, and aluminium cans.

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Advantages of the Extrusion Process

Drawing is the main process for making wire. Metal tubes and bars are more commonly sketched.

• It makes complex cross-sections simple to design.
• Materials that are brittle and ductile can both be processed in this way.
• High mechanical properties can be produced through cold extrusion.
• After hot extrusion, the product is still warm, making post-processing modifications easy.

Conclusion

Extrusion is a manufacturing process involving confining metal in a closed cavity and allowing it to flow through just one aperture giving the metal the shape of the opening. It works exactly like when you squeeze toothpaste out of a tube. The extrusion process is used frequently in moulding and shaping metals like steel and aluminium into forms we use, like your laptop or other home appliances. Products come in varying shapes and sizes, requiring metals to be moulded into shapes that give the product a sense of strength.

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