The process of injection moulding explained

Posted on 8 Sep 2014 by The Manufacturer

Injection moulding is a manufacturing process used to produce single parts and products using various materials, most commonly thermosetting and thermoplastic polymers.

Today, injection moulding is the most popular method of manufacturing parts and is used to produce a variety of everyday plastic products, including packaging, toys, telephones, bottle lids, chairs and many more. But just how does injection moulding work?

Electrical machine for plastic injection - image courtesy of Click Consulting.
Electrical machine for plastic injection – image courtesy of Click Consulting.

The machine

An injection moulding machine consists of a material hopper, a plunger and a heating barrel. The machine works to exert pressure and secure the mould in place during the injection process, and the type of machine that is used will be determined by the type of part being moulded and the material being used. For example, large parts and stiff materials will require machines that can exert a high clamping force and powerful injection pressure.

The process

Once the part for the product has been designed, the metal mould is precision-machined to create the desired shape, either as a single cavity or multiple cavities. The chosen material for the part, usually taking the form of plastic granules, is fed through a heated chamber and forced through a plunger into a hollow mould. After the cavity has been filled, the machine exerts pressure to ensure that the plastic does not collapse. The part then cools, solidifies and is ejected from the mould.

As well as the aforementioned process, there are various other injection moulding procedures, including metal injection moulding, die casting, thin-wall injection moulding and silicone rubber injection moulding.


To determine what type of material is used for the part, the particular function of the final product needs to be taken into consideration.

However, thermoplastics is usually the preferred material for injection moulding, mainly due to their desirable properties. Thermoplastics are recyclable, extremely versatile and will easily soften when heated. Thermosets and elastomers can also be used for injection moulding, although they are not as widely used.

Whilst the majority of moulds are constructed from steel, other metals including stainless steel, copper alloy and aluminium can also be used for specific procedures. Aluminium for example, is ideal for low volume production and large parts, but is unsuitable for high volume applications as it can be susceptible to damage.


There are a number of reasons as to why injection moulding is one of the most popular modern manufacturing techniques. Firstly, the procedure is quick and efficient, making it ideal for manufacturers to produce large amounts of identical objects with extreme precision and accuracy. Whilst the initial cost of injection moulding may be high, the ability for mass production is extremely cost-efficient way to manufacture goods.

Additionally, the shape of the mould can be as simple, or as complicated, as the design requires, from small components to entire car body panels.

To find out more about the types of products made using injection moulding, you can now visit online sites such as Display Developments.