How Does Injection Molding Work?


Injection molding is a production method for creating i […]

Injection molding is a production method for creating intricate pieces by injecting hot material into a mould, or 'die'. Injection molding can be carried out with a variety of materials mostly consisting of plastics, polystyrene, polycarbonate, glass, fibreglass, nylon, and most importantly thermoplastic and thermoforming polymers. The thermoforming polymer is the thermoplastics that change from liquid to solid in the presence of heat.

This process is normally referred to as 'injection molding' or as 'hot plastic injection moulding' (HPIIM). The process involves the filling of a cavity with the melted plastic material, the injection of the required number of moulds into the cavities and the cooling of the moulds after the material has cooled sufficiently for it to solidify. The cavities are called as inlets. The injection of the material into the moulds allows the tooling to form the desired shape.

The plastic parts made through injection moulding are known as polyethylene (PE), polystyrene (PS) and polycarbonate (PC). These are the three main categories of plastic materials used in the manufacturing of the injection moulding tools. The other material which can also be used in the production of these parts are metal alloys, thermoplastic resins and other thermoplastics. As polyethylene is a thermoplastic, so the plastic parts created through injection moulding need to be hardened by means of heat treatment. This process known as curing the plastic does not allow the plastic to move around before it hardens.

The injection moulding machines come in different models and sizes to suit the requirement of different manufacturing set ups. Large corporations and small to medium sized enterprises (SMEs) may choose from the high-tech injection moulding machines for mass production of the plastic parts. They have the capability to make thousands of plastic parts at a time. This machine is very user friendly and has a user-friendly menu to operate the processes. Also it has the capability to change the colour of the melted plastic, so that it matches that of the exterior part of the object being manufactured.

The injection process has to be started with the selection of the right sized hollow injection mould or 'nose'. This allows the feed mechanism to be placed into the cavity. The feeding procedure also determines the size of the internal cavity as well as the internal temperature of the material. The injection process also involves the selection of the appropriate nozzle for the melting process. This is essential because the shape and colour of the plastic material depend on the nozzle that is selected.

After the injection moulding operation is complete, the plastic material is removed from the cavities by means of vacuum pressure or a simple siphon. A cooling process is then required to remove the molten plastic from the moulds and the cavities. The cooled plastic is then passed through a heat-mold to harden it. When the hard plastic cools, it is then extruded from the mould in a cylindrical tube called the injection barrel. When the material is completely cooled, it is then passed through a cooling chamber to be dried and cleaned before being packaged.