The "plunger" style of injection molding machine is not commonly found in factories around the world, but is worth discussing due to its ingenious design and the availability in both horizontal and vertical configurations, as discussed in the "Verical Injection Moulding" blog.

The plunger design is semi-automatic in its design, meaning that the clamp holding the chamber is operated by lever-driven hydraulics or pneumatics, with the automatic type using an automatically driven cylinder to move the clamp into place when required. This allows a significant reduction in workforce leading to greater cost savings and faster run times, although it is more expensive to purchase than a conventional injection moulding machine.

The design was further refined with a two-stage design, which consists of two sets of plungers working in tandem, which first turn the resin into an injectable form and then pump the heated resin into the mould itself. This is an even more expensive version of the plunger type injection moulding machine, but it has advantages, such as requiring a smaller footprint in the factory and suffering no loss of pressure during compacting and heating of the resin.

The final iteration of the design is the 'Screw Plunger' moulding machine, whereby the first stage of the plunger was replaced with a rotating screw in order to process and melt the resin in order for it to be fed into the second plunger unit for injecting into the mould itself. This allows for better mixing of the resin, providing higher part quality, albeit with longer run times and higher initial cost.