Plastic Design - Which materials are suitable for bi-injection?

L'bi-material plastic injection also known as bi-injection, is a manufacturing technique that consists of combine two different polymers or two different colours in one plastic part. 

For example, a combination of soft and hard materials, such as your toothbrush that is made with a soft handle.

Pourquoi utiliser l’injection bi matière ?

The design of a high-performance product involves a design approach for manufacturing and assembly. This determines the future industrial life of the product. The challenge at this stage is to reduce or optimize the assembly and manufacturing phases. 

L’injection bi-matière permet la suppression de phase d’assemblage ou le recours à de la main d’œuvre directe pour la réalisation d’un assemblage de 2 matériaux différents.  Cela signifie un cycle time manufacturing shortera better quality control of the product, and a economy on the manufacturing cost.

To give you a clear idea of the benefits, here is a list of reasons why bi-material injection molding (bi-material injection) might be the right technology for a part or product:

  • Elimination of assembly step
  • Parts are well fitted and fixed, which makes the product more durable.
  • A wide range of appearance and customization options with numerous colors and materials
  • The manufacturing process is carried out with a single injection moulding machine, which means fewer upstream and downstream processes.

The material selection is first of all related to the application of the product. The functional specifications will provide a first series of answers as to the types of thermoplastics to be used.

The designer of the part will be in charge of dimensioning the component in an appropriate way, according to the constraints applied to the product, but also to the desired combination of materials. 

Mechanical or chemical clinging?

Literally, all thermoplastic materials can be used in bi-material injection. (if it makes sense for the function of the product). However, it is important to understand that some families of materials adhere more or less easily to another family.

Below is a tool to check the chemical compatibility of the two materials used in your design.





the materials you are considering do not adhere? no problem!

It will just be necessary to make mechanical hooks between the two materials, in order to keep them linked durably. 

Our teams of specialists are here to assist you in the design of bi-material parts. contact us