A Guide to Injection Moulding Process: Everything You Need to Know

Injection Moulding Process

Injection moulding is a manufacturing process that is widely used in various industries to produce complex and high-quality parts in large quantities. This process involves the melting and injection of thermoplastic or thermosetting polymers into a mould, which is then cooled and solidified to form the desired shape. In this article, we will discuss the injection moulding process in detail, including its history, equipment, materials, process steps, advantages, and limitations.

  1. History of Injection Moulding Process
  2. Equipment Used in Injection Moulding
  3. Types of Polymers Used in Injection Moulding
  4. Injection Moulding Process Steps
  5. Advantages of Injection Moulding
  6. Limitations of Injection Moulding
  7. Conclusion

History of Injection Moulding Process:

The injection moulding process was first invented by John Wesley Hyatt in 1868 to produce billiard balls. However, the early versions of injection moulding machines were manual and inefficient, with limited capabilities. The modern injection moulding process was developed in the 1940s, with the introduction of hydraulic systems and automated controls. Since then, the process has been continuously improved and refined, leading to the production of high-quality parts with complex geometries in large quantities.

Equipment Used in Injection Moulding:

The injection moulding process requires several pieces of equipment, including an injection moulding machine, a mould, and auxiliary equipment. The injection moulding machine is a large piece of equipment that contains a screw, barrel, heater, and hydraulic system. The screw is used to melt and inject the polymer into the mould, while the barrel and heater maintain the proper temperature and pressure. The hydraulic system is used to clamp the mould and control the injection process. The mould is made from two halves that contain the cavity and core, which form the desired shape. The auxiliary equipment includes a material hopper, conveyor belt, and cooling system, which are used to transport and cool the parts after injection.

Types of Polymers Used in Injection Moulding:

There are two main types of polymers used in injection moulding: thermoplastic and thermosetting. Thermoplastic polymers are the most commonly used type and can be melted and reshaped multiple times. Examples of thermoplastic polymers include polyethylene, polypropylene, polystyrene, and polyvinyl chloride. Thermosetting polymers, on the other hand, can only be heated and shaped once and then become rigid and cannot be reshaped. Examples of thermosetting polymers include epoxy, phenolic, and melamine.

Injection Moulding Process Steps:

The injection moulding process involves several steps, including material preparation, mould preparation, injection, cooling, and ejection. The following is a detailed description of each step:

Material Preparation: The polymer is loaded into the material hopper, where it is heated and melted. The material is then transported to the injection moulding machine.

Mould Preparation: The mould is clamped and prepared for injection. The cavity and core are lubricated and cooled, and the mould is preheated to the proper temperature.

Injection: The screw moves forward, forcing the melted polymer into the mould cavity. The polymer fills the cavity and solidifies, forming the desired shape.

Cooling: The mould is cooled to a temperature below the melting point of the polymer, allowing the part to solidify and harden.

Ejection: The mould is opened, and the part is ejected from the mould using ejector pins.

injection moulding process
A Comprehensive Guide to Injection Moulding Process: Everything You Need to Know

Advantages of Injection Moulding:

Injection moulding offers several advantages over other manufacturing processes, including:

  • High Efficiency: Injection moulding is a highly efficient process that can produce high-quality parts in large quantities at a low cost per part. This is because the process is highly automated and can run continuously without much human intervention.
  • Design Flexibility: Injection moulding offers design flexibility, allowing for the production of parts with complex geometries, precise details, and tight tolerances. This is because the mould can be designed to match the exact specifications of the desired part.
  • Material Versatility: Injection moulding can be used with a wide range of thermoplastic and thermosetting polymers, allowing for the production of parts with a variety of properties, including strength, flexibility, and durability.
  • Minimal Waste: Injection moulding generates minimal waste because the excess material can be melted and reused, reducing the overall material costs and environmental impact.
  • Consistency and Reproducibility: Injection moulding offers high consistency and reproducibility, ensuring that each part produced is of the same high quality and meets the exact specifications of the design.

Limitations of Injection Moulding:

While injection moulding offers many advantages, there are also some limitations to the process, including:

  • High Initial Costs: Injection moulding requires a significant initial investment in equipment and tooling, making it less viable for small-scale production runs.
  • Design Constraints: Injection moulding requires careful design considerations to avoid problems such as sink marks, warpage, and air pockets. This can limit the design possibilities and add complexity to the production process.
  • Material Selection: Injection moulding requires the use of specific types of polymers that can be melted and injected into the mould. This can limit the selection of materials based on the desired properties of the part.
  • Lead Times: The design, manufacturing, and testing of the mould can take several weeks or even months, leading to longer lead times for production runs.


Injection moulding is a highly efficient and versatile manufacturing process that has revolutionized the production of complex and high-quality parts. The process involves the melting and injection of thermoplastic or thermosetting polymers into a mould, which is then cooled and solidified to form the desired shape. While injection moulding offers many advantages, such as design flexibility, material versatility, and high consistency, there are also limitations, such as high initial costs, design constraints, and longer lead times. Overall, injection moulding is a valuable process that has contributed significantly to the manufacturing industry and will continue to play a critical role in the production of high-quality parts in the future.