An Essential Guide to Plastic Injection Moulding

Plastics have become an integral part of the world market. In today’s global economy, virtually every industry relies on plastics. This is because plastics are a durable, cost-effective, and flexible choice of material.

They come in different forms, shapes, and sizes, which makes them the ideal solution for making whatever you can think of today; iPhones, laptops, utensils, electronics, appliances, farming tools, you name it.

In this guide, you will learn the basics of plastic injection moulding.

What is Plastic Injection Moulding?

Injection moulding is a form of plastic processing that involves the injection of heated, liquefied plastic into a temperature-controlled mould under high pressure. After filling the mould, the plastic cools and solidifies into finished part(s) that can be easily removed when the machine opens up.

This process is performed in specialized injection moulding machines (IMMs), which range from micro IMMs to very large IMMs (usually exceeding 3,000 tons of clamping force that can hold large moulds).

Each production sequence, i.e., from the closing of the mould to the injection “shot” to the opening and removal of the part, is a “cycle.”

Different Plastic Manufacturing Processes

Before delving into why injection moulding is ideal for plastic manufacturing, it is important to outline the different methods of plastic product manufacturing.

High Volume

High volume outputs require large machinery to manufacture plastics on a mass production scale. It involves:

  • Extrusion Moulding
  • Blow Moulding
  • Injection Moulding

Low Volume

These methods use purely grinding and cutting procedures for shaping. It involves:

  • Fabrication
  • CNC machining
  • 3D Printing

Medium Volume

Medium Volume is the most effective procedure for moulding and shaping plastics. It involves:

  • Casting
  • Thermoforming
  • Rotational Moulding
  • Compression Moulding

Why Injection Moulding is Ideal for Other Processes

There are many reasons why injection moulding is preferred over other plastic manufacturing processes.

  1. First off, the injection moulding process is very simple to use. It involves only two steps which are obtaining the mould and using the mould to create parts.
  2. Plastic injection moulding is preferred for its ability to facilitate large production processes of identical parts.
  3. This method uses automated vision inspection to ensure accuracy and consistency in delivery. It handles prototypes of complex geometry in a precise, fast, and highly efficient manner.
  4. What’s more, this resourceful method delivers high strength and flexible qualities of the post-mould product.
  5. Another reason is that plastic injection moulding is the least expensive way to produce parts in medium to high volumes.
  6. Injection moulding is the most popular method of dealing with diverse plastic types simultaneously. This helps you save on both operational and manufacturing costs.
  7. Finally, it is an environmentally friendly method of manufacturing plastic.

Injection Moulding Process Steps

Assuming that the mould has already been created, injection moulding consists of six steps.


Typically, injection moulds are made in two, clamshell-style pieces. In the clamping phase, the two metal plates of the mould are clamped together in a machine press.


After clamping, an injection can begin. In this phase, the plastic (which takes the form of pellets or granules) is melted into a liquid. Then, the liquid is injected into the mould.

NB: Manufacturers should ensure that the temperature stays constant throughout this step of the process.


In this phase, the melted (liquid-form) plastic fills the entire mould. Here, pressure is applied directly to the mould to ensure the liquid occupies the cavity and the product comes out identical to the mould.


In the cooling phase, the mould is left alone to cool and solidify into a useful product that can be removed from the mould without compromising it.


After cooling, a clamping motor will slowly open the two parts of the mould to ensure the safe removal of the final product.


With the mould open, an ejector bar will slowly push the solidified product out of the open mould cavity. Then, a fabricator will use cutters to eliminate any waste material and make the final product ready for consumer use.


Waste material can be recycled and reinjected to minimize your material costs.

Major Applications for Injection Moulded Parts

The key applications for injection moulded parts include:

  • Automotive
  • Consumer electronics
  • Packaging and beverage bottling
  • Industrial components
  • Consumer products
  • Medical devices
  • Construction and building

Quality Control and Potential Defects

Although the plastic injection moulding process is highly effective in manufacturing various plastic products, defects can still take place from time to time.

For instance, in the manufacturing of phone cases, defects such as dent, contamination, chipping, stain, scratches, stain, diameter, height, thickness, flatness, positioning, absence presence, mark reading and more can happen.

In this scenario, the use of an automated vision inspection solution can reduce the defects to a minimum.


The plastic injection moulding process can be challenging. However, once the first mould is created, injection moulding is the most cost-effective and fastest way to create countless identical parts in manufacturing today.

Since quality control is the main concern for all manufacturing processes, the adoption of AOI (automated optical inspection) solutions in plastic injection moulding plays a vital role.

An AOI machine such as the Nova Series has powerful checking, sorting, and marking capabilities, and it is heavily used in the plastic injection moulding industry for inspection of critical plastic parts.

This allows manufacturers to cut down on defects and save cost and time while improving their business reputation and customer satisfaction.