What Is Injection Moulding and How Does It Work?

Pens , electrical fittings, automobile parts,LEGO bricks,action figures, syringes all these objects have one thing in common , they are made by injection moulding. But what exactly is this process and why have people been using it for over 150 years and still continue to use it today ?

At GANTOOLS we have spent over 2 decades perfecting this process helping entrepreneurs, visionaries and product teams to turn their concepts into production ready reality.

200 ton Injection moulding machine

What is injection moulding?

It is an industrial process that converts plastic granules into a required shape.

Why is it used so widely?

1. It is overwhelmingly cost effective in high volume production. Real life example from us, the value of an identical part comes down from Rs.1080 ($12.24) using 3d printing to Rs.34 ($0.39) using injection moulding.

2. It produces near identical parts every single time so a minimal QC is sufficient.

3. A wide range of engineering materials can be used. Recent developments in plastics allows us to replace steel parts.

4. Many required finishes from matte like to glossy can be achieved

What is the procedure?

Before we understand the procedure there are some terms we have to be familiar with.

Mould: It is a specially designed and precision machined tool that contains a hollow space (of part profile) in the shape of the required product.

Injection moulding machine: It is a machine which takes in plastic as raw material and uses the mould to produce the finished parts.

Master batch: These are additives added to the plastic raw material in specific ratios to give the desired properties to finished product. eg colour,UV resistance

1. Material preparation:

   1. The required raw material and masterbatch are mixed in specific ratio

   2. [optional] Material is pre-heated to remove moisture before production.

2. Machine preparation:

   1. The prepared raw material flows into the machine barrel.

   2. The heating elements of the machine is switched on brought to the required temperature ( example: 210~220 C for PP )

   3. The mould is either externally heated or gets heated up after a few shots.

   4. The cooling circuits are switched on to prevent overheating.

   5. The process parameters are fine tuned temperature, pressure,cooling time etc.

   6. the produced parts are checked by a QC personnel and is fine tuned as needed.

3. The moulding cycle :

   1. Material Loading: Plastic granules (like ABS, Nylon, or PP) are fed into a heated barrel.

   2. Melting & Injection: The granules melt and are injected under high pressure into a mould cavity.

   3. Cooling: The mould keeps the part’s shape as it cools down and solidifies.

   4. Ejection: Once cooled, ejector pins push out the finished part.(Other ejection technologies like air ejection , strip ejection which dont leave any marks exist and can be used by us)

4. Post-processing:

   1. Degate and deflash : the pipelines in mould used for plastic flow into the part are still attached to the part (called runners) after ejection .They have to be removed either automatically or manually. (We use submarine gates to automatically separate parts from runners during ejection )

      *We use hotrunner in high volume production or special cases to make the parts without runner.

   2. Cleaning: Some products require cleaning ( medical / critical engineering components) which are usually cleaned with IP (Isopropyl alchohol)

What are some common defects and how do we tackle them?

Shortfill : Caused when not enough material is being fed into mould or if an air vent has been blocked. This can be resolved by changing the feed rate or by removing the block.

The expected shape

Shape due to shortfill

Look at that excess material !

Overpacking : caused when too much material is fed into the mould. this can be mitigated by reducing the feed stroke.

That is a silver streak

Silver streak : caused due to mould temperature problems or improper material preheating.These can be mitigated by proper temperature control.

Notice the depressions in the component that is shrinkage

Shrinkage: Lack of material packing caused by reduction in hold time. Can be mitigated by adjusting hold time or pressure.

Final Thoughts

Injection moulding isn’t just a process — it’s where design meets engineering.

From a startup prototyping its first product to an OEM scaling up production, it remains one of the most reliable and cost-efficient manufacturing technologies.

If you’re developing a new product and want to explore injection moulding 👉 Get in touch with Gantools and let’s bring your idea to life.

A video for you of a working IMM

Notice how the runners are already split from the part that is a submarine gate