3 key questions on injection moulding (thermoplastic injection)

Below are our workshop leader’s answers to a selection of frequently asked questions about thermoplastic injection.


How long does it take to design a mould for thermoplastic injection?

Creating an injection mould requires between 5 and 12 weeks. The production time of the mould for thermoplastic injection depends on the complexity of the mould. The mould is composed of two halves, a fixed part and a moving part. If the geometry of the parts is complex, it will be necessary to add movements (demoulding of undercuts) to remove the part from the mould. Ribs may also be inserted to provide mechanical reinforcement. The ribs increase the complexity of the injection mould and the production time. It is possible to reduce the manufacturing time by simplifying the design of the mould.

In addition, other parameters influence the production time of a thermoplastic injection mould:

  • The number of impressions (multi-impression mould or not)
  • The type of steel used: a hard steel takes longer to machine. Aluminium, which is softer, is faster to machine than steel for example
  • Any surface treatments
  • The finishing of the parts (mirror polishing, etc.)

How many plastic parts can be produced with an injection mould?

The number of plastic parts produced by a plastic injection mould can vary from several thousand to several million units. The main factors are as follows:

  • The type of steels (aluminium, steel, etc.)
  • The type of plastics (PP, PE, ABS, reinforced or not reinforced material, etc.)
  • The number of press assemblies/disassemblies and production start-ups
  • The quality of the press

Thus, the lifetime of the injection mould depends on its quality and the materials used during its manufacture. These materials have a strong impact on the price. However, they must be selected primarily according to the technical needs. In addition, the heat treatments applied must be chosen according to the steels. It is essential to find the appropriate treatments at the risk of destroying the impressions. Taking care of the mould makes it possible to increase its lifetime and the number of parts that can be created.

What parameters determine the price of a plastic injection mould?

The factors determining the cost of an injection mould are related to the manufacturing time, as we have seen above:

  • The number of impressions: the simpler the design of the injection mould, the lower the price.
  • The type of material used to make the injection mould. This depends in particular on the quantity of parts to be produced. In general, aluminium will be cheaper than steel.
  • The type of injection required.

It is important to note that the price of a plastic injection mould is amortised by the quantity of parts produced. An injection part can cost between a few cents and a few euros. This price depends on multiple elements, the main ones being the following:

  • The size of the part and its complexity
  • The material used
  • The number of impressions

If you are hesitant about choosing this technology for your project, you can consult the advantages and limitations of thermoplastic injection.

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