Overview of the Plastic Injection Molding Process

Plastic injection molding utilizes the high-pressure injection of melted plastics or resins into custom-designed molds to produce solid plastic parts and components. This highly versatile method is used for the production of a variety of products made from a broad selection of plastic materials compounds.

Compared to other plastic manufacturing processes, plastic injection molding offers several advantages, including higher precision parts and the facilitation of more cost-effective high-volume runs.

The following article provides an overview of plastic injection molding, including outlining the steps of the process, common plastics and resins employed, key considerations, and how to select the right injection molding partner.

The majority of plastic injection molding operations include the following steps:

The part designer/engineer or project manager chooses a material that demonstrates the proper performance and production characteristics for the desired part or component.
The molding operator feeds the selected compound into a barrel heater that contains a reciprocating screw and heated runners to melt and direct the material.
The reciprocating screw and/or runners heat the plastic or resin into a melted liquid state, and the screw moves the melted material down the barrel toward the injector nozzle.
The nozzle injects the material at high speeds into a steel or aluminum mold in the shape of the desired part or component. The injector pressure and timing ensures that all sections of the mold are filled.
The injected material cools into the shape of the mold and then ejects the solid part from the mold manually or through the use of ejector pins.

All of the parameters of the injection molding process-including the cycle and injection timing, injection pressure, and cooling time-are determined based on the material and product design.