How Does Injection Molding Work?

What is Plastic Injection Molding?

Plastic injection molding refers to the manufacturing process used globally, to produce various types of plastic items. These items spans from the smallest of toys to agricultural crates to the body panels of automotive vehicles. The list is simply endless.

Plastic Helical Gears and Worm Gears

Plastic Helical Gears and Worm Gears

Brief History

It is on record that 1872 was the year that saw the patent of the first injection moulding machine. The inventor used Celluloid as the material for the production of simple, every day items. Examples of plastic items produced back then are hair combs, cases, etc.

However, after World War II, technological innovations got better. This led to the improvement of the injection molding process, which in turn led to the development of the screw injection method that is still in use today.

How it Works

The injection molding process is known for its ability to produce parts in large quantities quickly and consistently. Have you ever wondered how it works?

One important thing that you will need for the process is an injection moulding machine. It may sound simple - forcing molten plastic granules into a mold until it fills the mold, sets, and assumes the shape of the mold. However, there are several components and processes involved in injection molding.

Injection Molding Machine

First off, it is important to know that the injection moulding machine is made up of three main units, and they are:

  1. The Feed Hopper
  2. The Heater Barrel
  3. The Platens
  4. 550 Ton Full-Electric Injection Molding Process

Each of the units performing different functions to facilitate the molding process effectively and efficiently.

240 tonnes Injection Molding Machine

240 tonnes Injection Molding Machine

Injection Moulding Process Flow

  • The polymer granules/ plastic pallets are dried first before being mixed with the pigment that gives them their different colors (if needed). After all that, they get poured into the hopper.
  • Next, the granules from the hopper feeds into the heated barrel. The heated barrel is where the mixing and melting of the polymer granules take place. The molten plastic then get moved along to the mold by a turning screw in the injection barrel. The screw and barrel, are designed to create buildup of pressure to melt the solid polymer granules in a process called plasticizing. Interestingly, different types and grades of polymers require different setting and processing conditions to plasticize.
  • There is a forward movement by the ram. This force from the movement injects the melt through a small orifice at the barrel tip into the mold. The molten plastic then fills up the whole cavity, and the part forms taking the shape of the cavity image. Simultaneously, the water-cooled channels built in the mold speeds up the solidification process of the melted plastic in the mold.
  • The next cycle is the cooling process of the material, and after it has cooled down, the melted plastic re-solidifies, and this time it assumes the shape of the cavity in the mold.
  • After the cooling cycle, the mold opens. Then, the mold's ejector pins will push out the solid plastic part.
  • Mold closes thereafter and the next cycle begins.

The entire molding cycle of a plastic part can take anywhere from 15 to 90 seconds depending on part size and wall-stock thickness.

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Several reasons why injection molding is the better manufacturing choice

  • Injection Molding is very suitable for production of shapes that are complex. At the same time, other manufacturing methods may not be economically viable.
  • There is a wide range of materials to use, and this makes it possible to get different items to get created for different purposes.
  • It may interest you to know that injection molding is quicker and more affordable than some other alternative methods.
  • With injection molding, mechanical properties can be tailored with visual appearances that are appealing.
  • The plastic injection molding process is low-cost in large volume production runs, and its impact on the environment is minimal

The possibilities of injection molding are endless. Consequently, a lot of companies opt for injection molding, as opposed to other available methods. Plastic is an inexpensive material, and the whole process of producing the plastic items can be very economical.

Electric Car - Electronic Part - Plastic Injection Molding


Every year we see the development of new types of plastic compounds. On top of that, the techniques for mold making keeps developing and getting better. Hence, it is indicative that plastic injection molding method is here to stay.

In addition, new technological innovations keep emerging, they enhance the efficiency and effectiveness of the injection moulding process. Consequentially, productivity and quality of materials improves dramatically.

Keen to find out more about plastic injection molding as your product's manufacturing solution? Connect with us via our chat button on the bottom right of the screen.

Find out more about our capabilities and experience in plastic injection mould and molding here.

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