Injection Moulding: How It Works and Its Significance in Modern Manufacturing


Injection moulding is the most common method for mass manufacturing plastic products. This process has revolutionised the production of countless everyday items, providing an efficient and versatile solution for creating complex plastic components. Here, we delve into the historical context, the detailed injection moulding process, and the innovations that have shaped this critical manufacturing technique.

Historical Background

The inception of injection moulding can be traced back to the late 19th century. The need to find a substitute for ivory in billiard balls led John Wesley Hyatt to develop celluloid, one of the earliest plastics. In 1872, Hyatt patented an apparatus for moulding products from celluloid, marking the advent of plastic injection moulding. This innovation laid the groundwork for modern injection moulding techniques that are fundamental to today’s manufacturing industry.

The Injection Moulding Process

The basic principle of injection moulding involves melting plastic, injecting it into a mould, allowing it to cool, and then ejecting the final product. An injection moulding machine typically comprises three main components: the injection unit, the mould, and the clamp.

Detailed Process

Plastic Pellets
The process begins with feeding plastic pellets into the hopper. These pellets are then transported forward by a screw inside the barrel over a one-way valve called the screw tip assembly.
Heater bands surrounding the barrel warm the plastic pellets. As they move forward, they melt, forming a molten plastic mass at the end of the screw in front f the one-way valve screw tip assembly.
Plastic Injection
Once molten, the plastic is injected into the mould cavity by the screw acting as a plunger.
Plastic Injection
Within the mould, the plastic solidifies, usually within a minute. Ejection: The mould opens, and ejector pins push the cooled part out before the mould closes to repeat the cycle.

Innovations and Improvements

Significant advancements have been made since the early days of injection moulding. One notable innovation is the introduction of the reciprocating screw, which ensures even heating and thorough mixing of the plastic. The shearing action of the screw generates friction that aids in melting the plastic, enhancing the efficiency of the heating process.

Mould Design

  • Vents: These allow air and gas formed from the polymer to escape from the mould as the plastic is injected, preventing defects.
  • Coolant Channels: These channels circulate coolant to speed up the solidification process.
  • Ejector Pins: These pins push the cooled part off of the mould.
  • Sprues and Runners: These channels guide molten plastic to the mould cavities. Advanced setups, such as those used for Lego bricks, employ hot runners to maintain the plastic in a molten state right up to the point it enters the cavity.

Practical Examples

Injection moulding is used to produce a vast array of products. Lego bricks are a prime example, known for their precise moulding process involving hot runners and clever draft angle designs. Additionally, many everyday objects, from electronics cases to cutlery, are manufactured using injection moulding.



Pioneered by John Wesley Hyatt, injection moulding remains a critical and evolving manufacturing process. It continues to produce billions of products annually, demonstrating its enduring importance and versatility in the modern world.

Ledwell Plastics harnesses the power of injection moulding to deliver high-quality, technically advanced mouldings. Our expertise in mould design, rapid prototyping, and sustainable plastics ensures that we meet the diverse needs of our clients while upholding the highest standards of quality and efficiency.

Would you like to learn more about our injection moulding capabilities or any of our other services? Contact our team for customised solutions tailored to your requirements.

Relevant links:

  1. British Plastics – A leading trade association for the UK Plastic Industry, providing valuable resources and industry updates.
  2. – An association of plastics manufacturers with extensive information on plastics production and sustainability.
  3. Injection Moulding – A comprehensive resource for news, technology, and trends in the injection moulding industry.
  4. – A leader in 3D printing technology and rapid prototyping services.
  5. Plastics – A publication offering in-depth articles and insights into the latest in plastics technology and injection moulding.
  6. Polymer – Provides testing, consulting, and R&D services for polymers and plastics.
  7. – A platform with resources and articles related to engineering, including injection moulding.
  8. British Standards Institution (BSI) – Source of standards and certifications relevant to the plastics industry.
  9. TWI (The Welding Institute) – Offers insights and resources on welding and joining technologies, including those relevant to plastic fabrication.
  10. Society of Plastics Engineers (SPE) – An international organization providing networking, training, and knowledge-sharing opportunities for plastics professionals.

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