Injection moulding of plastic

Injection moulding is the most common method used for manufacturing plastic products and components.

Injection moulding is best suited for manufacturing series of more than a thousand units. The method is ideal for making dimensionally accurate products. The result is neat and has little need for post-processing. The advantages of injection moulding are speed and the high quality of the product. The raw material is usually a thermoplastic (remeltable) polymer, but the method is also suitable for thermosetting plastics.


Small changes, big impact

The injection moulding process is highly automated, but the production of a high-quality and cost-efficient plastic product requires experience and versatile know-how. Small changes in the speed or temperature of the cycle can have a big impact on productivity or the durability and strength of the object. The professionals at Leomuovi and the modern machinery they use guarantee high-quality products and customer satisfaction.

Injection moulding machine

The injection moulding of plastic is performed by an injection moulding machine, which is made up of five sections: the clamping, injecting, hydraulic, and control units and the frame. Each section is a separate functional unit. In addition to these, the injection moulding machine needs a mould specific to the product.

Stages of the injection moulding process

  • Plastification

  • Injection and holding pressure

  • Cooling

  • Extrusion


The raw material is melted or plastified to an injectable state using pressure, friction, and heat. It is important that the temperature of the mass is as even as possible throughout the injection dose during plastification. The mass must have even distribution of colourant and possible additives. The raw material must also retain its original properties during the injection moulding process as far as possible.


Once the raw material has reached the desired temperature it is injected in to the mould. About 95 % of the mould cavity volume is filled. The injection stage takes between about 0.1 seconds and a couple of seconds, depending on the thickness, size, and shape of the object. Holding pressure follows immediately and pushes the plastic into the details of the mould. Holding pressure must be applied long enough so that no irregularities, bubbles, or warping form on the surface of the object.


The cooling stage is the longest stage during injection moulding. The plastic mass already begins to cool during the injection stage as the mass flows into the mould. Cooling is however continued after the holding pressure has been released in order to keep the object in the right size and shape and to prevent warping. The object is removed from the mould only after it has hardened sufficiently and there is no danger of warping. Cooling is often sped up by using water to cool the mould.

Extrusion or removal from the mould

Once the object is cool and hard enough the mould opens and the object is removed from it. The object must remain intact during extrusion and it must not have any permanent marks. The strain caused by extrusion must be evenly distributed through the object.


Great products are a result of flexible collaboration and genuine commitment.
Our job is to support your product development and supply you with reliable, high quality plastic parts – no matter how simple or challenging the product.

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Leomuovi has been delivering injection molded parts and goods to both industry and consumers for more than 30 years. Leomuovi’s main focus is on contract manufacturing and our services are used in numerous industries, for example:

  • Construction
  • Electronics
  • Machinery
  • Ventilation and air conditioning
  • Metal working
  • Furniture manufacturing
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Methods and materials

We use the latest technology and methods to ensure optimal results. For manufacturing plastic products and components, we use injection moulding, which is best suited for manufacturing large series. For sealing, we use an automated production line, which ensures the high quality and repeatability of products.

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Thanks to our joint efforts and enthusiasm to create valuable products, Leomuovi Oy is growing sustainably and continuously. Nowadays our factory manufactures a broad palette of customized industrial components and appliances from different commodity and engineering plastics.

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