Extrusion Process: Definition, Working Principle, Types, Applications, Advantages, and Disadvantages [Notes with PDF]

Introduction

In the field of mechanical engineering, the Extrusion Process is widely used by engineers to form an object which has a fixed cross-sectional area. For making an object, the raw material is pushed into a die to provide it with the desired shape. The major function of the extrusion process is that the brittle materials can easily be turned into the desired product. It can be argued that extrusion is a semi-continuous or even a continuous process that can be used to form hot or even cold material.

What is Extrusion?

Extrusion is a type of metal-forming operation where dies are used to change the shape of the metal piece. This is done with the help of external force which is compressive in nature. Through this process, we can make any type of complex shape quite easily.

Working Principle of Extrusion

The required amount of force in the case of the extrusion process is given by a plunger or piston to produce the compressive force. The following is the working principle of the extrusion process:

• At first, an ingot or a billet of a standard size is developed by the manufacturer.
• Then the billet is heated at a higher temperature and it is stored for a long time at room temperature to push it in the press.
• The billet is pushed by the plunger mounted in the press towards the die by providing compressive force.
• High compressive force helps the material to achieve the desired form.
• Lastly, the material is taken out from the press and after that, it needs to be passed through the finishing process in order to enhance its mechanical properties.

Types of Extrusion

Extrusion can be broadly classified into two types:

• Hot Extrusion
• Cold Extrusion.

They are further categorized into the following categories:

Hot Extrusion

• Forward Extrusion
• Backward Extrusion

Cold Extrusion

• Forward Extrusion
  • Hydrostatic Extrusion
  • Hooker Extrusion
• Backward Extrusion
  • Impact Extrusion
  • Cold Extrusion Forging

Hot Extrusion

In a Hot Extrusion process, a workpiece or billet is heated above the recrystallization temperature. It is then loaded into the container while the ram exerts a force on it. As the workpiece is already heated above the recrystallization temperature, it is quite easy to flow through the die and is also very accurately and effectively reshaped.

The common materials used in this type of extrusion are Magnesium, Copper, Steel, Aluminium, Nickel, etc.

Cold Extrusion

In this process, the workpiece is kept at the normal room temperature, or you can say below the recrystallization temperature. To extrude any product through this process huge amount of force is required.

Indirect Extrusion

In this process, the direction of the force applied by the ram and the direction of extruded metal is on opposite side. This type of extrusion is also called as backward extrusion. The main advantage of this mode of extrusion is that it reduces friction comparatively. Also by this process, we can extrude metal of relatively less diameter. 

Direct extrusion

In this type of extrusion process, the direction of the ram and the direction of extruded metal are in the same direction. This mode of extrusion is also called forward extrusion. The main advantage of this process is that by using this type of process we can extrude longer workpieces. 

Hydrostatic extrusion

In this type of extrusion, we use fluid to pressurize the billet. At first, a billet is loaded into the container. We then need to fill the container with fluid generally castor oil. The container is then closed except for one side of the container, which contains a ram and a piston. To keep the operation smooth the shape of the billet is maintained conical so that it can easily pass through the die.

When we start the machine, the ram exerts a high amount of pressure on the fluid. It is then transferred to the billet. Due to the highly pressurized fluid, plastic deformation takes place inside the billet and then it comes out from the other side of the die and gets the shape of the die. The main advantage of this process is that a very less amount of friction force comes into action as there is no contact between the container wall and the billet. Hydrostatic extrusion is usually performed at room temperature.

Hooker Extrusion

This is quite a popular extrusion process, by which thin-walled seamless copper or aluminum tubes are produced. At first, the billet or the blank is placed in the container. A punch exerts a force on the workpiece and makes the workpiece into a cup shape. In the next step, the longer length will punch again and make it a long cylinder-shaped product, and the thickness, as usual, reduces as well.

Impact Extrusion

In an Impact Extrusion, a punch is struck to the workpiece at a very high speed to produce an impact load. It can be of any type namely forward, backward, or even both. It is generally done at room temperature i.e. Cold Extrusion. If we need products like a cup, toothpaste cover, or any hollow section we generally do Backward impact extrusion which is quite a popular impact extrusion process.

Cold Extrusion Forging

Cold Extrusion Forging is a backward extrusion process. The process of Cold Extrusion forging is the same as that of Impact Extrusion. In this process, the movement of the punch or ram is a little bit slower as compared to Impact Extrusion.

Applications of Extrusion Process:

• The extrusion process is mainly used in the formation of hollow pipes and it can also be used in the production industry. Apart from that, for making instant foods and snacks type products, extrusion process is preferred by manufacturers. In the case of food processing, extrusion process is used to heat the product and develop a liquid stage of the product. Also, in cooking, the extrusion process is used nowadays which includes mixing, shearing, separation, cooling, heating, etc. For removing the moisture from the products and also for encapsulating material, the extrusion process is taken into account by the producers.
• However, to develop ready-to-eat material cold extrusion process is used. As an example, pasta is manufactured with the help of a cold extrusion process. These types of products are incorporated with low moisture due to which the life cycle of products is increased and also it is more convenient to serve the customers.
• Pharmaceutical products are also developed with the help of the extrusion process. Polymeric filters and nonporous goods are formed through the extrusion process. The making process of drugs includes both hot as well as cold extrusion processes. To increase the solubility of products and bioavailability, hot extrusion process is used. In this process, a high amount of pressure, heat, and agitation is taken into account by manufacturers.
• Apart from this, in structural work, the aluminum extrusion process is used. This process includes doors, windows, etc. In an automotive industry, the extrusion process is also used to form the desired type of material by using brittle materials.
• Lastly, it can be said that the extrusion process is widely used to make plastic materials.

Advantages of the Extrusion Process:

Extrusion includes several advantages which are as follows;

• The extrusion process is widely used to create a complex profile of materials within the least time as compared to other metal-forming processes.
• The extrusion process is very useful to work with brittle and ductile materials.
• Mechanical properties which can be developed by the extrusion process are very precise and enhances the life cycle of products.

Disadvantages of the Extrusion Process:

Some disadvantages of extrusion processes are listed below:

• The time consumption of this process is very high.
• The set-up cost is also very high.
• The amount of compressive force required for the extrusion process is very high, and due to this, the operator needs to ensure that the plunger is fixed in the press appropriately.

FAQ’s

Conclusion:

We can conclude by saying that it is a widely used manufacturing process. It is highly consistent and has higher accuracy. The extrusion process is likely to continue to develop and used widely in the future too.

To learn about more processes check out the pages below.

• forging Process
• Forming Process
• Rolling Process
• Heat Treatment
• Die Casting