The way the Injection Moulding Machine works

Injection molding is the world’s most widely used production method when it comes to creating plastic products and parts. But how does an injection molding machine actually work? How do the different machines differ from each other? And how big does your production series need to be before injection molding becomes cost effective?

The way the injection moulding machine works

An injection molding machine works like a large-scale press. After liquid plastic has been injected into the mold, the injection molding machine keeps it closed and stable at full force.

The cycle starts when the machine is filled with granules. The granules are sprayed into the cylinder, where they are heated until the material is liquid. The screw located in the cylinder compresses the material at the front of the cylinder. The compressed liquid polymer is then injected into the mold cavity. When it is completely full, the machine maintains the strong pressure. This is an essential step to compensate for material shrinkage.

The screw then reverses for another shot of granules in the cylinder. The product in the mould cools down, and when the temperature of the product is low enough, pens push the product out of the machine.

Now the machine is ready for the next product.

How do injection molding machines differ from each other?

The big difference between injection molding machines is the amount of closing pressure they can deliver. This pressure keeps the mold closed during the injection molding process. The pressure can range from 5 tons to more than 3000. In order to produce without problems, the pressure must be high enough to keep the mold closed while the liquid plastic is sprayed into it.

Want to know how much pressure you need for your product? This is determined by the size of the product and the number of cavities in the mold. As a rule of thumb: closing force = injection pressure x projected surface of the product x safety factor. The safety factor is often set at 1.5.

But remember: the raw material also plays an important role in determining the optimal closing pressure. When the material is very rigid, then it will need a little more pressure to successfully fill the mold.

injection molding construction site

What production volume is needed to take advantage of injection molding?

Injection molding is a production method to produce high volumes of identical products at high speed. Although the building of tools (such as a mold) requires an investment, you benefit from a low cost per product. Fortunately, nowadays some injection molding companies have optimised their production process so that the method is profitable for lower volumes as well. These days it is possible to produce a series of only a 1000 pieces efficiently.

Are you in any doubt?

Your injection mold partner will help you select the right mold, design and suitable material for the production quantity you need.

Let us help you to produce your plastic product