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Plastic Injection Molding

PacZone Boxes
Plastic Injection Molding

What is Plastic Injection Molding?

Plastic injection molding is a production procedure whereby the molten thermoplastic material is injected into the relatively cool cavity to create an article of the desired shape. Plastic injection molding is a manufacturing technique for making custom size plastic packaging boxes or parts from plastic material. Molten plastic is forced, at high pressure, into a mold cavity which is in the inverse shape of the desired product. The mold is constructed in the mold workshop from metal, usually either mold steel or aluminum alloy, and precision-machined to form the features of the desired part. Injection molding has been widely used for manufacturing custom boxes and parts, from small components to large car panels.

The process of plastic injection molding

An injection molding machine generally consists of four basic parts: the clamping and ejecting unit, the injection unit, the electric driving unit and the hydraulic control unit. The clamping unit is there to hold the mold during the injection and cooling. Basically, it holds the two halves of the injection mold together.

During the injection phase, raw plastic material, usually in the form of granules, are loaded into a hopper on top of the injection unit. Though some injection molding companies like PacZone has robotized the injection procedure, thus the feeding has also been automated, where hoppers are put separately from the machine and collectively on the feeding room. The granules feed into the cylinder where they are fastly heated to reach the molten form. Within the heating cylinder there is a motorized screw that mixes the molten granules and forces them to end of the cylinder. Once enough heat-softened plastic material has accumulated in front of the screw, the injection process begins. The plastic fluid is forced into the mold through a gate, while the screw controls the pressure and speed.

The dwelling phase acctually means a pause in the injection process. The molten plastic has already been injected into the mold cavity and certain pressure is applied to make sure every slightest corner of the mold cavity is filled.

Then the hot plastic fluid is allowed to cool to its solid form within the mold cavity. The clamping unit will then release, to allow the two halves of the mold open. An ejecting rod and plate will then eject the finished piece from the mold. That’s one cycle done.

Advantages of Injection Molding

- High tolerances are repeatable

- Wide range of materials to use

- Low labor costs

- Minimal scrap losses

- Little finish needed after molding

Disadvantages of Injection Molding

- Expensive equipment investment

- Setting up costs may be high

- A specific must be built for each part (or set of parts).


Injection molding is not new for custom plastic parts manufacturing. It is a fast & efficient process and used to produce large numbers of identical items, be it disposable consumer goods or high precision engineering components. It produces such small products as bottle tops, watch packaging boxes, children's toys, candy gift boxes, containers, disposable razors and parts of cameras and so on!

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