What is Injection Molding? Definition, Materials, Products

Injection molding machine
Injection molding machine
Resource: https://www.youtube.com/watch?v=ckWi-rOxPzo

In the world of manufacturing, injection molding is one of the most popular parts-making processes. Businesses use it to create everything from medical supplies and housings for consumer electronics to components for the automotive industry. Learn injection molding with this overview.

What is Injection Molding?

Let’s start with the basics of injection molding. What does it mean and where did it all start? Injection molding refers to the parts-making process where molten material is directed into a mold and cooled to create a specified product. Here is the deeper injection molding meaning as well as its history.

Injection Molding Definition

Injection means to fill, and molding means to shape. So injection molding is defined as a type of manufacturing process where molten material (usually plastic) is injected into a two-part mold using tremendous pressure. The mold is then cooled, and the finished product is ejected.

The injection molding manufacturing process allows for the production of parts with very precise dimensions and a high level of repeatability. This manufacturing process is also relatively quick, making it ideal for large production runs.

Injection Molding History

The history of injection molding begins many years ago, in the 1800s. During that time, people were experimenting with various manufacturing processes. Around 1872, John Wesley Hyatt developed the first injection molding process.

The injection molding machine has evolved significantly since that time. And while there are several types of injection molding today and more material options, the core principle is still the same – which brings us to the question…how does it work and what materials are used?

Injection molding animation
Injection molding animation
Resource: https://www.youtube.com/watch?v=fUrJyd2vTFk

How Does Injection Molding Work?

Polymer (or other material) pellets are placed into the heated barrel of an injection molding machine, mixed, and forced into a mold cavity. The mold is clamped shut with tremendous force and out comes the desired shape! Here is how injection molding works:

Injection Molding machine

The equipment where everything takes place is called an injection molding machine. These machines come in a variety of sizes, from the small desktop injection machine to large, industrial-sized units.

The parts of an injection molding machine include: the hopper, injection unit, the mold and clamping unit, and the ejection system. The hopper is where the raw material is stored before feeding it into the injection unit, while the mold receives the molten material to shape it.

The clamping unit holds the mold closed during injection, and then opens it when the part is ejected from the machine. On the other hand, the ejection system removes the parts from the mold after they have cooled.

Injection Molding Process

The injection molding process steps, from feeding raw materials into the machine to molding the part and finishing touches are outlined below.

  • Injection molding raw material, usually in pellet or granular form, is fed into a hopper. The hopper, in turn, feeds the material into a heated barrel.
  • The injection molding barrel is equipped with an auger system that pushes the raw material forward while compressing it. This action mixes and melts the material, making it easier to inject into the mold cavity.
  • When the molten material reaches the required conditions, the screw pushes it forward into the mold. Here, the material is forced to move around and fill up the entire cavity of the mold, creating a replica of its shape.
  • Once it has cooled completely, the part is ejected from the mold, usually by the use of ejection pins. The parts are then collected, trimmed to remove any excess material, inspected for quality and defects, and then finished as required before being shipped.

The entire injection molding process takes just a few seconds to minutes to complete and can be repeated over and over again to create large quantities of products. It also produces parts with complex shapes and tight tolerances compared to many other manufacturing processes

Injection molding plastic
Injection molding plastic
Resource: https://www.bloomberg.com

Injection Molding Materials

Injection molding offers excellent versatility when it comes to the types of materials that you can use. Apart from the many different types of plastics, other injection molding materials include metals, glass, and ceramics.

Plastic Injection Molding

Plastic injection molding is the most popular type of the process. It is also the most versatile, as you can easily utilize it to produce all sorts of plastic parts. Some of the most popular plastics for injection molding are:

  • ABS (acrylonitrile butadiene styrene)
  • PC (polycarbonate)
  • PA (polyamide/nylon)
  • PS (polystyrene)
  • PET (polyethylene terephthalate)
  • PVC (polyvinyl chloride)

Metal Injection Molding

In metal injection molding, metal in the form of powder is mixed with a binder material and then made into pellets. These are then heated and the melt pushed into a mold, where it cools to a solid. The most commonly used metals for injection molding include:

  • Stainless steel
  • Titanium alloys
  • Copper alloys
  • Carbon steel
  • Nickel alloys

Glass Injection Molding

In very recent times, it has become possible to inject-mold glass, although research is still ongoing. A polymer binder is infused with silica (glass) particles and fed into a molding machine. The molded part is then washed to remove the binder, heated to remove more binder, and sintered to fuse the silica particles.

The glass injection molding procedure requires less heat and can create very small, transparent glass parts, something that was not previously possible. Glass parts produced via injection molding are perfect for scientific, medical, and consumer applications such as.

  • Tiny optical components
  • Lenses
  • Glasses
  • Solar cells
Injection molding chair products
Injection molding chair products
Resource: https://www.youtube.com/watch?v=ATiG11Qhe-M

Injection Molding Products

Injection molding uses in the manufacturing industry are one of the most diverse. It can produce a range of parts, from small components to larger structures, and its applications are virtually limitless when it comes to the types of products that can be manufactured.

Note that this technique is mostly used to create thin-walled parts, as the process enables a high level of precision and detail. The result is a product that meets exact specifications. These are some of the most popular injection molding products:

  • Automotive components
  • Medical devices
  • Electrical enclosures
  • Packaging products
  • The housings of consumer goods and appliances
  • Mechanical components such as gears

Injection Molding Vs. Blow Molding

Injection molding and blow molding are two popular methods for making plastic parts. While both involve a few similar steps, some distinct differences set them apart.

  • The injection molding technique typically requires the use of a mold to shape the part, while blow molding relies on air pressure to form the part.
  • Injection molding process is better suited for creating parts with complex shapes and intricate details, while blow molding is often used for hollow containers.
  • In terms of cost, injection molding is usually more expensive than injection molding, as it typically requires more specialized and costly molds.
  • However, if the parts require complex shapes or intricate details, injection molding will often be more economical in the long run

To sum it up, injection molding and blow molding are two distinct processes that both have their unique advantages and disadvantages. Depending on your specific application, one may be better suited than the other.


Injection molding is an incredibly useful method for manufacturers, allowing them to produce complex parts in high quantities quickly and efficiently. The technology continues to evolve with the introduction of newer materials, such as those used for glass injection molding, enabling manufacturers to make products that were not previously possible.