What is the Plastic Injection Molding Process?

Harriette Halepis

When thermoplastic and thermosetting plastic materials are produced, this process is referred to as the plastic injection molding process. In order to create these products, material must be heated, mixed, and placed inside of a mold. When the mold cools, the material is extruded resulting in specific objects.

Plastic auto-rickshaw made with multiple injection-molded parts.
Plastic auto-rickshaw made with multiple injection-molded parts.

While plastic may seem like a relatively new invention, the first plastic object was actually created in 1851. A British inventor by the name of Alexander Parkes created a material that was then called Parkesine. Even though Parkesine proved to be both durable and innovative, it was also highly flammable, so it did not enjoy a long lifespan. In 1868, an American inventor by the name of John Wesley Hyatt developed a similar product that he dubbed celluloid. After joining forces with his brother, Hyatt created the first injection molding machine in 1872.

Colored pellets used for plastic injection molding.
Colored pellets used for plastic injection molding.

This injection machine revolutionized the way that objects were made. Items such as buttons, hair combs, and collar stays could be produced in this way. When the 1940s rolled around, the process became an essential part of the manufacturing business. Consumers demanded inexpensive products, which also had to be inexpensive to produce. Plastic was relatively cheap, so it grew in popularity.

Car dashboards are created with plastic injection molding.
Car dashboards are created with plastic injection molding.

The plastic injection molding process changed as a whole when the first screw injection machine was created in 1946. James Watson Hendry's screw injection machine allowed manufacturers to have more control over plastic injections. It proved to be such an advancement that many of the machines used today still function in the same manner. Once it was discovered that the process could be so precise, plastic replaced other materials, such as steel and ceramic.

Today, nearly every plastic item — milk caps, car dashboards, combs, phones — is created with plastic injection molding. In many different ways, plastic has replaced most other materials. Due to its flexibility, versatility, and reliability, plastic objects are popular around the globe.

The injection molding process makes it possible for manufacturers to create thousands of products at once. In addition, labor costs are relatively low within the plastic industry, and parts can be refined following the injection process. The main drawback to injection molding equipment is that it is often expensive to maintain and purchase. Still, plastic proves to be one of the most widely produced materials in the world.

Plastic injection molding revolutionized the way items like hair combs are made.
Plastic injection molding revolutionized the way items like hair combs are made.

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Discussion Comments


@dobie - You are right in that you can't waste what you don't have, but I don't see how regulating companies--and households for that matter--solves the bigger problem of lack of education.

You can ban all plastic injection molding equipment and all plastic products outside of the commercial and healthcare field and you still haven't accomplished the purpose of making people more sensitive to their environment. Instead of throwing out plastic it will be some other material. And then we'd have to ban those, too.

I'm not trying to be argumentative at all...I totally get where you are coming from and agree with you, actually. But there has to be a better solution to the problem and I think that would be education. Access would help as well.

We live in a rural area and there aren't many ways we can recycle without driving way out of our way to do it. Our trash company provides a small container for recycling, but not all households in our community use a waste disposal company. Providing easier, more accessible receptacles for recycling would be a huge step in the right direction.


@babiesX3 - Oh, I know there is no way to regulate...the plastic injection moulding process is just too big at this point. I wasn't saying we should stop using plastic altogether. I just meant that there has to be a way to control how much of it is going into the landfills every year.

I agree that people should be educated, but how? Efforts have been going on for decades about the importance of recycling and people still don't get the picture. Or if they do understand they simply don't care. My thing is that it would be impossible to create the waste on the household level if the plastic was not so readily available in everything we buy.


@dobie - While I certainly see and respect your point, I don't see any way for that to ever happen. Plastic is everywhere and in everything. If it's not in the actual product then it's used to package the product.

I love my resuable plastic bottles and plastic dishes that I don't have to worry about breaking when I need to travel with food. My father in law actually works with a plastic injection molding machine and his trade has provided him with reliable work in one of the worst possible times to try to find a job. Plastic has it's benefits, as does the making of plastic.

So, while there is a danger to the environment when people are irresponsible about their trash and recycling, I don't think regulating the entire plastic industry is the answer. Why not redouble the efforts to educate and inform society of what they can do to help the environment...while enjoying their plastic products?


I find it amazing, and somewhat alarming, how dependent our society as a whole has become on plastic. I don't mean anything negative; great advances in healthcare and other areas have been made on account of plastic. On the other hand, it has created a wealth of unnecessary products that clutter up landfills year after year.

I think that maybe some sort of regulation should be put on the types of products that can be made out of plastic. Of course, I realize this is a completely impractical idea, but think of how better off our environment would be without plastic molds for virtually everything we use.

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