Injection Moulding Processes


What is Injection Moulding?

Injection moulding is a mass production process capable of creating multiple quantities of solid plastic parts repeatedly at fast cycle times. Consequently it is very suited for high volume manufacturing.

Moulds, also known as tools within the industry, are created using specialist machines.  As well as containing the shape of the finished part they have to withstand the high pressures involved, provide a channel for the molten plastic to flow into the mould, extract heat from the part and provide a method of ejecting the part once it is has solidified

The injection moulding machines are available in different sizes and are usually rated by the locking force (required to keep the mould closed) and shot weight (the amount of plastic that can be injected).

Plastic granules are fed into the injection moulding machine which are then melted. The machine then forces the molten plastic material into the empty cavities of the moulding tool under high pressure.

After the cavities have been filled, the hot plastic material begins to cool. As the plastic cools it begins to take the desired shape, determined by the moulding tool. Cooling times vary depending on the size and complexity of the part and also the specific materials being used. Cooling of the component is carefully controlled and is carried out by circulating water or oil through the mould tool. Once the part has cooled sufficiently, the tool is opened and the finished moulding is ejected and removed from the machine by a robot. Once the injection moulded plastic part has been removed from the tool and clear of the machine, the tool then closes to repeat the process.

High-quality tools are essential for a successful injection moulding process. It is important to design tools that perform efficiently and can make high-quality components with a long life expectancy.

Injection Moulding Cycle Times

The cycle time of the injection moulding process is defined by the time it takes to make a complete part from closing the tool, injecting the plastic, cooling the polymer under pressure, opening the tool and ejecting a full part. A short cycle time will improve manufacturing efficiency, allowing more parts to be made for the customer in a shorter time. A short cycle time is also paramount to achieve a competitively priced component.

Multi-Cavity Tooling Options

Each tool can consist of one or multiple cavities. These can be identical to each other or unique to allow one tool to produce differing sets of components. For high volume requirements, it is ideal to design a tool that will make more than one identical part at a time.

For example, pre-form plastic components for making plastic bottles are produced in tools of up to 160 identical cavities. Accurate tool-making and precise process control are required to ensure that all cavities are created equally in multi-cavity moulds.

Additional Injection Moulding Services

There are a number of additional processes to compliment a plastic injection moulded part, many of which are available at RGE.

Automatic application of self-adhesive labelling is available at RGE on many injection moulded parts. Alternatively, detailed markings and stunning graphics can be applied to cooled components using Computer Controlled Pad (Tampo) Printing. This method offers a premium finish to any product.

Simpler decoration can also be added, such as company logos or product markings. These can be carried out with the application of hot-foil blocking, usually during the cooling cycle of the plastic injection moulding process.

Plastic components can be assembled using ultrasonic welding or linear vibration welding. RGE make complex base components for products such as tumble-dryers using the linear vibration welding technique. The method joins a lower and upper part with a water tight welding joint to make a stable and accurate complex plastic component.

RGE’s experience stretches across many other plastic moulding and welding applications and we produce in excess of 23,000 tonnes of injection moulded plastic components every year from over 160 injection moulding machines. With an injection moulding machine clamp force capacity ranging from 25t up to 3150t, RGE can cover the full spectrum of any injection moulding requirement 

If you have any further questions regarding the injection moulding processes and how RGE can you help you with your requirements, please contact us on 01480 450771.

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