Plastic Injection Molding and its Working Explained in the Easiest Way

Plastic Injection Molding and its Working Explained in the Easiest Way

Plastic Injection Molding and its Working Explained in the Easiest Way

Have you ever wondered how mineral water companies get their 3d printed bottles? 

Or how biscuit companies get packets for their products? 

Well, today, we discuss something called plastic injection molding.

What is Plastic Injection Molding?

Plastic injection molding, in simple terms, is the industrial process of creating mass identical plastic products by following certain design guidelines. In today’s world, it is one of the most used ways for creating a number of similar stuff at a time using cnc machines.

According to research, enough plastic is thrown away each year to circle the earth four times. 

Well, it might not necessarily be a good thing, but what it shows is how plastics have been an integral part of our lives. From simple household utensils to flying planes, humans use plastics as raw material for products everywhere, and plastic injection molding is the easiest way of us getting an abundance of custom plastic consumer products through plastics technology.

How Does Plastic Injection Molding Work?

If you are just scanning through this article and want to know the basics, here it is. 

  1. What we basically do is go through a material selection process and place the common plastic resins in an injection machine. 
  2. The machine has a heated barrel or hot runners where the plastic material melts. 
  3. After that, the liquid is injected into the mold with a single cavity (which is inside the device as well) where we tune it into a specific shape using injection molding design. The cycle time, injection time, wall thicknesses, injection pressures, and other parameters are fixed according to the design for manufacturability.

Detailed Way of Working of an Injection Molding Machines

An injection molding machine consists of four major parts- the feed hopper, screw, heated barrel, and the mold cavity.

Injection molding involves two basic steps:

  • Melt Generation by a rotating screw.
  • Forward movement of the screw to fill the mold with melt and to pass the injected melt under high pressure.

First, we use a hopper and runner system to place the granular plastic into a heating barrel carefully. 

There’s a reciprocating screw inside the barrel which creates heat with a frictional force with heater bands. The plastic melts there. 

As the machine is still moving (with the help of the screw), the plastic is then injected through a nozzle from where it gets inside a mold cavity through a gate system. It almost looks like a tunnel. 

Finally, we get the desired shape of the plastic resins, which cools as it is inside the cavity.

While the plastic is inside the cavity, the machine applies a holding pressure. If you didn’t know, particles expand when they heat. 

When the plastic inside the mold cavity cools down, its volume will decrease as well, so we need some pressure to compensate for that.

We use ejector pins to take the material out from the machine after it solidifies. 

As the screw moves, another batch of granular plastic is fed to the heating barrel. The process continues from there, and the ejector pins help remove the injection molded plastic after it cools and hardens.

Types of Plastic Injection Molding

There are generally three type of injection molding machines:


1. Hydraulic Injection Molding

It is the first and the foremost type of injection molding machine which has been around for centuries. 

We use something called the ‘hydraulic oil,’ which means using liquid to create pressure during the injection molding process. This oil is used inside a hydraulic motor, which in turn rotates the screw.

One of the major considerations in hydraulic injection is creating leak-free systems for the molding process. 

The hydraulic oil could leak inside the plastic, which will create irregularities. So, we need expert seal design considerations to cover the motor.

Hydraulic Injection Molding has been present since the earlier times and is still operated by various factories in the world. 

The relatively lower cost and ease of maintenance of this injection molding machine have been the two major factors for people being interested in it for insert molding.

Pros and Cons of Hydraulic Injection Molding Machine


  • They are cheap to buy and have better injection rates.


  • They have better ejection capability given that they are more potent than other injection molding machines.


  • They are available in abundance all over the world, so it is effortless to get spare parts.


  • Hydraulic Injection Machines have a larger shot size so they can accommodate a lot of products.


  • It provides accurate design because of the clamping force it provides.


  • The modern advances in this machine have introduced gas accumulators, which make this machine faster.



  • Leaks happen in a hydraulic injection molding machine. So, you can expect to clean it a lot.


  • The same goes for your place; you will need some work to keep it tidy.


  • The power consumption can raise concerns for many. Generally, hydraulic injection machines eat up 5.12 kWh of energy during a process.


  • Sound pollution- hydraulic injection machines make a loud noise.



2. Electrical Injection Molding

The problem with hydraulic injection molding is that even if it is effective, it is not efficient (the machine works fine, but we can’t say the same for energy consumption). 

Well, Japan introduced the first electrical hydraulic machine in the 1980s, and it has been used as an alternative to the bulkier hydraulic machine ever since.

An electrical injection molding uses high-speed servo motors.

It is easy to use and is advanced. 

The machine is cost-efficient given the comfort and speed of production it provides. At the same time, an electric hydraulic machine needs less maintenance and has a digital control option, which means we can set the energy and pressure credentials to how much we need.

Pros and Cons of Electrical Injection Molding Machine


  • Electrical Injection Molding is effective and works fast. Industries can create a whole lot of product in a short while.


  • There is no fluid associated so the workplace will remain hygienic.


  • Electrical Injection Machines don’t make a lot of sounds.


  • It has lower power requirements as we can digitally control the output levels.


  • We don’t need a lot of maintenance. Thus, it has a little operational cost.


  • The work is precise, and we get great plastic shapes.



  • These lines of machines don’t produce as much as clamping force as hydraulic injection molding.


  • Of course, we don’t need to maintain it frequently. However, if some problems come out of nowhere, we are bound to have some difficulties as parts are not readily available.


  • It costs more than hydraulic machines.


3. Hybrid Injection Molding

This molding method is the mix of both hydraulic injection molding and electrical injection molding. 

It was produced with the addition of both molding benefits and has proven to be better than the former two types.

This method of molding has a high level of flexibility and holds the selling quality of both the previous two types of molding machines. 

It can save energy like an electrical system, providing the accuracy of the hydraulic unit at the same time. 

It can alternate between the DC pump motors and the hydraulic pump, so both of them operate only when they are individually required. Due to this, there will be no quality compromises.

Pros and Cons of Hybrid Injection Molding Machine


  • It provides excellent results with very flexible control of energy level outputs.


  • Hybrid Injection Molding is your answer if you want to gain high-quality output, saving bills at the same time.


  • This machine is high-speed, so expect a great response time.


  • The machine doesn’t heat so frequently and seems to need less maintenance.



  • In most of the cases, we need to assemble the machine depending on the user’s requirement.


  • The architecture is very specific- only the party who built it can maintain it.


  • The workforce should be trained to use both electrical and hydraulic system.


Advantages of Plastic Injection Molding

As we know, humans need plastic goods. Plastic injection molding is one of the most comprehensive ways of getting that, so it has helped make humans’ day to day lives more manageable.


I. Accuracy

Plastic molding is accurate and holds the capacity of manufacturing almost every part from plastics. 

The theory of this procedure – first, melting the plastic and then fine-tuning into a piece – means we can get any shape out of plastic molding.


II. Fast method

Injection molding is a quick and easy method of creating plastic goods. 

In most of the cases, the cycle of production lasts for 15 to 20 sec. 

However, the speed of work is dependent upon the structure of materials.


III. Low Operating Cost

Plastic injection molding usually works automatically, which helps in minimizing the cost of supervision. 

It additionally keeps operation well optimized and production in progress.

So, instead of having to hire different people for different tasks, you can teach one of your employees to operate the machine.


IV. Sustainable Method

It is necessary for manufacturing companies to look over the environmental cons and pros through their production. 

Plastic injection molding is not only practical but also a sustainable method that decreases ecological consequences. 

Plastic injection molding process only uses limited resources for production and focuses on recycling more than a new product.


V. Flexibility

As you can see, injection molding has advanced a lot. 

You have plenty of options for technology and machines. At the same time, as injection molding is common throughout the world, you can easily get the human resources to fix in case something goes wrong.

How to Choose an Injection Molding Device?

Generally, only a person who has been working in a molding company has an idea to distinguish between right and wrong device. So, your best bet would be to visit a company and ask for recommendations.

Additionally, particular products need to be equipped with special devices such as accumulators, closed circuits, injection, compression, etc.  

The critical factors that often affect the selection include molds, plastics, products. 

Below are some points that you should update yourself before choosing the device for injection molding:


  1. Mold type, its weight, height, design, etc.


  1. Type of plastics, quality


  1. Size of the product


  1. Molding requirements, product quality, production speed


  1. Model of the injection molding machine


Remember, these are just some considerations, and there might be hundreds of factors depending on your specific needs. 

It is one of those things that you must talk to an expert about to get right.

On top of that, buying a factory machine with just a little information by yourself might turn your money into a bad investment.

We don’t need to make the article unnecessarily long and confusing for you with jargon. 

Just visit a manufacturing engineer and tell them about your product requirement. Then, they will be able to help you.


Plastic injection molding is the easiest way to make thousands, if not millions of identical products from plastic. 

It is an economical method when we look at what it does. 

This factory technology is at a very advanced state, so you get an abundance of options. 

However, you will need to talk to an expert before purchasing an injection machine for your purposes.


We are the best precision molding team in Malaysia. Call now and get a quote!




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