Basics of an injection molding machine

Basics of an injection molding machine


An injection molding machine also commonly called an injection press, is the machine used to produce plastic parts using the injection process. It is basically achieved through heating and clamping. It also has two basic parts the injection unit and the clamping unit. This article will explain the basics of an injection molding machine.


To explain the process in layman’s terms the machine works by feeding resin or material into the machine, colorants or other materials are added, it is then heated and pressed together to form the desired shape or form and then ejected from the machine. There are also two types of machine orientation, horizontal and vertical. A lot of injection machines are horizontally oriented, but for those that require insertion these types are vertical oriented.

There are three stages in completing the whole injection molding process:

  1. PLASTICATION – raw materials are sent forward by a rotating screw into a barrel, while the barrel is heated from the outside. The screw charging in and out of the barrel will stir and cut through the plastics, thereby causing gradual plastication.
  2. INJECTION – when the screw stops rotating, the clamping part begins to close the mold and the injection unit takes its place to few the molds together, the injection pressure and speed as required by the molding techniques inject the fused plastics into mold cavity.
  3. MOLDING – the materials in the fused cavity are then cooled, the plastic parts are then ejected from the chamber thus the process of the molded plastic part is completed.

The whole injection cycle is completed by these three steps. The cycle is just repeated until the manufacturer gets the right number of products produced.

The injection molding machine also has two types:

Plunger injection Molding Machine.
  • The machine pushes forward the materials in the barrel by the to and fro movement of the plunger while the spreader injects them further into the mold through a nozzle. Plastication occurs when the barrel starts to be heated from the outside, when there is no sufficient heat this result in poor plastication. Plunger injection molding is not best for molding plastics are too heat sensitive and have low fluidity.

Screw injection Molding Machine
  • In place of the horizontal plunger, this type of injection molding, machine instead has a screw in place of it. The screw can move in and out of the barrel and is able to send materials, compact and plasticate as well as transfer pressure. This type of machine has more yields and is highly productive among the injection molding machines.


To understand how the injection molding machine works will help the manufacturer choose the best one for the type of part or piece that will be created. The process of injection molding is just a continuous cycle. As one cycle finishes, another one starts. Finding the right type of injection molding machine that will fit the specifications of the piece to be manufactured will help reduce costs in the end-product, minimize wastages, maximize productivity and labor costs.

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