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What is Injection Moulding?

Injection Moulding

Injection moulding is a manufacturing process where parts are produced by injecting molten material into a mould. It can be employed to produce prototypes, or for full scale mass production volumes where high volume units of identical items are required.

Injection moulding can be carried out using several different materials, such as metals and glasses. However, for the purpose of this article, we will be focusing solely on its more commonly used material: thermoplastic polymers.

The Injection Moulding Process

The first stage of the injection moulding process is the creation of the mould tool itself. This will be made from metal, usually aluminium or steel. At RP Technologies, we mostly manufacture tooling in aluminium. There are several reasons for this. Aluminium Tooling provides greater speed of manufacture, is a more cost-effective solution, and it is more suited to low volume manufacturing. It also reduces time to market for new products.

Our tools are all made in-house by our skilled and experienced toolmaking team, who precision machine them to match the features of the product. The tool design is created, prototyped, and tested using computer aided design, or CAD.

Each mould tool has two parts: the cavity and the core. The cavity is the fixed part, and the core is the moving part. At RP, we create tools that are capable of producing parts which often have complex design features.


To test the tool, a suitable thermoplastic must be selected. Choosing the correct type of plastic for the end application is essential, in order to ensure that the final component has the right properties. Each thermoplastic has different characteristics and behaves differently when exposed to high temperatures, chemical substances and different pressures. This is due to its molecular structure.

Once the optimum plastic has been identified, the moulding process can begin. Plastic polymers, or pellets, are fed into the machine, and begin a slow passage through the barrel where they are heated until they become molten. The pellets are then injected into a clamped mould. This is known as the shot.

Once the molten plastic has been injected into the tool, the cooling process begins immediately. The tooling is heated or cooled, depending on the type of polymer being moulded, to give optimum cycle time and product quality to the moulded component.

As soon as this stage in the process has been completed, the solid plastic product can be ejected from the tool by purpose-built mechanisms known as ejector pins.

When the ejection is complete, the clamp is shut again, ready for the cycle to begin once more.

In some instances, finishing processes may be required, such as polishing or removing excess plastic.


Advantages of Injection Moulding

Ideal for projects which require high repeatability

Highly efficient process which allows for potentially hundreds of parts to be created in short cycles

Design flexibility – allows for complex components, shapes and geometries to be achieved

High levels of product consistency – essential for projects where tight tolerances are required

Enhanced strength – fillers, additives and additional moulding services such as insert moulding can make for more long-lasting products

Greater flexibility of material choices and colours

Recyclability of material – material waste can be reground, melted, recycled and reused

Injection Moulding by Industry

Injection moulded parts are everywhere. In your office and in your home. We are surrounded by plastic injection moulded components. They are produced everywhere for universal consumption.

But there are several key industries that have come to rely on the injection moulding process more so than others. Let’s take a closer look at some of these key market sectors….

Medical – High standards of quality are key for medical devices and equipment, which is what makes injection moulding such a popular choice for designers and manufacturers within this marketplace.  RP Technologies has helped bring to market many medical products, including surgical instruments, drug delivery systems, housing for monitoring apparatus, diagnostic test kits and prosthetics.

Consumer Products – The production and consumption of consumer products would not be possible without injection moulding. Toy manufacturers are particularly reliant on the process, in order that they can create identical plastic products that are safe, durable, versatile and visually appealing.

Electronics – Similar to the world of telecommunications, the electronics industry relies on the injection moulding process to produce plastic components which can house complex wiring, circuit boards and cables.

Telecommunications – The injection moulding process allows manufacturers to supply telecommunications companies with plastic housing units, attachments, adapters and other parts to facilitate the transmission of data and information through countless numbers of fibre optic cables.


Automotive – Injection moulding allows for the mass production of highly repeatable parts which are high quality, reliable and consistent. This makes it an ideal manufacturing partner for the automotive industry. If advanced automation techniques are available, the injection moulding process can also be very cost-effective. Injection moulded components also offer weight saving opportunities by utilising metal replacement polymers to reduce overall vehicle weight and increase fuel efficiency.

Aerospace – The high level of product consistency associated with injection moulded components means that tight tolerances can be achieved. This is particularly important for industries such as the aerospace sector, where safety, quality and component integrity are of the utmost importance.

RP Technologies has many customers in each of the above industries, as well as in other industries. We are specialists in producing high quality parts on time and to a high standard. We have a reputation for specialising in complex component designs which many of our competitors would not be willing to produce. That is why we are the first choice for many product designers and engineers.

If you have an injection moulding project which you would like to discuss, please contact us at, or call +44 (0) 121 550 5868, and we will be happy to assist you.

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