- Injection moulding is a manufacturing process for producing parts by injecting molten material into a mould. Injection moulding can be performed with a host of materials mainly including metals, (for which the process is called die casting), glasses, elastomers, confections and most commonly thermoplastic and thermosetting polymers. Material for the part is fed into a heated barrel, mixed (Using a helical shaped screw), and injected (Forced) into a mould cavity, where it cools and hardens to the configuration of the cavity.
Recent development in plastic injection moulding
Gas-assisted injection moulding
In this form of injection moulding, the typical melted plastic injection is assisted by the injection of pressurised gas into the mould – nitrogen is commonly used for this process. The gas generates a bubble that pushes the plastic towards the ends of the mould. As the bubble expands different sections are filled. There are several forms of moulding used in the plastics industry that are differentiated by the position where the gas is injected when casting the polymer.
More specifically, gas can be injected through a nozzle in the machine, or directly into the mould’s cavity under a constant pressure or volume. Some of these methods are protected by patents; therefore proper licencing agreements should be entered into the use of them.
Foam injection moulding
This technique provides an effective, affordable way to achieve high resistance and rigidity in structural parts. In addition to this advantage, structural foam parts have a superior thermal isolation, a greater chemical resistance, and improved electric and acoustic characteristics. These parts involve a foam core between two layers; this core is obtained by dissolving an inert gas in the resin and allowing it to expand when injecting the gas-plastic solution in the cavity of the mould. This process is used in vehicle panels as an alternative to reduce part weight.
Thin-wall injection moulding
The main technological innovation in this case is related to the end result. A section with very thin walls. The major difficulty of this process is to decide what width the wall should be for it to be considered a ‘thin wall’. As a general rule, when component parts have widths under half a millimetre (1/50th of an inch) they are considered to have thin walls.
The benefits associated with the reduction of the wall’s width are highly appreciated and sought after nowadays.
Multi Component Injection Moulding
Also known as injection over moulding or over injection, since this process involves over moulding a hard or soft polymer over a base material (substrate), which is generally a plastic or metallic component.
Overall, this technology can be defined as the injection of more than one component or material within one same mould and as part of a single process, allowing for the combination of two, three or more materials with different colours, textures and shapes.