Types of Plastic Injection Molding Machines and Processes

The plastic injection molding machine is the most preferred machine for production in large volumes. The common materials used for injection molding include thermosets and thermoplastics. A machine heats and mixes the plastic until it liquefies before it’s fed into a mold. When the molten liquid cools down, solidifies, and takes shape in the mold, the mold is opened, and the finished product Is revealed.

Below is a list of the different types of plastic injection molding machines and how they work

Compression Molding

Compression molding is the opposite of injection molding. The melted plastic is poured into the mold, which is closed after. There’s a hole in the mold where another device can apply pressure. The pressure pushed the plastic outward into the mold’s cavity, where it takes form and shape. Compression molding is mainly used to manufacture items that have excess plastic that should be trimmed off. Compression molding can be used to manufacture rubber items.

Transfer Molding

This type of plastic injection molding is similar to compression molding but needs a metal plunger to provide pressure. The molten material is poured into the molded and closed up. Then a metal plunger shaped like a large shaft is used to apply pressure on the mold pushing the molten material to fill up the space in the mold. This type of plastic injection molding can be used on plastics or rubbers.


Extrusion is a molding method that can work on hot or cold material. In extrusion molding, a die is used against a three-dimensional mold. A die is a two-dimensional hole with a defined shape through which a material is extruded. The extruded material(metal, aluminum, or plastic) takes on the shape of the die. Continuous extrusion means the production of long extruded pieces, while semi-continuous extrusion involves the production of the same-sized pieces.

Blow Molding

Blow molding is almost the same as compression molding but uses pressurized gas to pressure the plastic to take the shape of the mold. The molten plastic is poured into a mold and covered. There’s a small hole in the sealed mold through which the pressurized gas is pumped. The gas may compress, but it still creates enough outward pressure so that the plastic fills out the mold.

Rotational Molding

Rational molding uses rotational motion to pressure the molten material into the geometry of the mold. Molten plastic is fed into a mold and closed. The mold then rotates, which enables the molten material to fill out the shape of the mold.


Hydroforming is a molding technique (metal-specific) that uses water to pressurize metal into a die or mold. The metal is then heated to an alterable but not molten state before it’s poured into the mold and sealed. A small hole in the mold allows water to come in at high hydraulic pressure. The pressure of the water makes the metal fill out the mold. The water is later removed, and the finished product is revealed.


Laminating is an easy type of plastic injection molding that applies pressure on a sheet of plastic, mostly a laminate, onto a substrate. The laminate often overlies the substrate, and another sheet on the other side is forced to join the first sheet. The force to join the plastic to the substrate comes from heat or physical pressure from a block.