Injection molding is one of the most common procedures in the production industry. By heating up materials to convert them into liquid form and trapping them within a mold, various forms of objects are created. Alongside CNC machining, injection molding is among the most popular forms of fabrication techniques and is considered a conventional method.

With the advent of 3D printing, injection molding is becoming less popular, but regardless, it’s one of the go-to solutions especially for mass production use cases.

Substances Used in Injection Molding

The materials commonly used for this procedure include different polymers that react well to heat. But other substances such as metal and glass are also used for certain applications to create hybrid designs of multiple materials.

Some of the commonly used polymers are Acrylonitrile Butadiene Styrene (ABS), Polyoxymethylene (POM), Polycarbonate, Thermoplastic Polyurethane (TPU) and Thermoplastic Rubber (TPR) among many others. These are all used for different applications due to their varying nature, for creating keycaps, DVDs, knife handles among other things.

How Injection Molding Works

While there are many intricate parts that work together to make the injection molding procedure work flawlessly, it can be summed down into 4 major components that really get the job done:

The Process


Initially, the mold has to be held securely with the help of a clamping unit. A mold has two sides, one of which will be able to move while the other will be held firmly with the help of the injection molding machine. A motor at the end of the injection machine helps open and close the mouth of the mold.

It’s important that the right amount of clamping pressure is applied, or else the mold will come loose, spilling all of the injection that will later on be added to the mix.


Once the mold is held securely, it’s safe for the material to be poured into the mold. The material can be any form of thermoplastic polymer and usually exists in granular or pellet form. First it gets melted down, and is gradually added into the mold. It’s held down within the internal walls of the structure where it starts to take the shape of the container.

The injection procedure works for a wide variety of shapes and sizes, helping create very intricate shapes without losing out on any structural integrity.


Arguably the most important process in ensuring good results during the injection molding procedure is getting the material to cool down properly. After being poured into the mold itself, the material will begin to cool down and take the shape of the container around it.

There’s a chance of shrinkage as well, so material and mold design considerations have to be made so you get the most out of it. Different procedures have different cooling requirements, with various methods and factors contributing to different results.


Once the entire procedure is complete, the pertaining problem is to eject the plastic itself from the mold. Modern installations have an ejection system, which are particularly handy as the cooled down material can bond itself with the insides of the mold.

There are different techniques for carefully removing the material, ranging from a mold release agent to air ejection which can get the material out of the socket without causing any damage to it.

Benefits of Injection Molding

Despite it’s complexities, injection molding allows the creation of a wide array of structures that can endure a lot of force while being complex in their designs. The initial cost of the tooling and other preparatory material for injection molding is high, but creating the various units for design per unit is fairly cheap, similar to 3D printing.

It’s common for injection molding to be automated and the procedure is preferred when the volume requirements are particularly high.

Alternatives to Injection Molding

The most common alternative to injection molding is 3D printing. The procedure is the way to go for prototype development, as it takes significantly less time in material fabrication. For smaller businesses, 3D printing is a better option for producing goods as the initial cost for development is lower.

About the Author

The author of this post deals in injection molding and other design services at Connekt. LLC. The company is operational in Grass Valley and Auburn, providing mechanical and engineering design services, custom injection molding, custom plastic parts, finite element analysis and consulting services and various other offerings. You can reach out to them for your engineering and design needs.


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