Plastic Design - Which materials are suitable for bi-injection?
Plastic Design – Which materials are suitable for two-component injection moulding?
Two-component plastic injection moulding, also known as bi-injection, is a manufacturing technique that involves combining two different polymers or two different colours into a single plastic part.
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.
Why use two-component injection moulding?
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 Moulding 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:
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- Elimination of assembly step
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- Parts are well fitted and fixed, which makes the product more durable.
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- A wide range of appearance and customization options with numerous colors and materials
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- 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. Le cahier des charges fonctionnel apportera une première série de réponse quant aux types de thermoplastic"thermoplastics à utiliser.
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.
Materials Compatibility Chart
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
❓ Frequently Asked Questions
What is two-component injection moulding in plastics processing?
Two-component injection, also known as bi-injection or overmoulding, is a technique that combines two distinct polymers or two colours in a single part. It is carried out in a single operation on a multi-component press or in two operations with a rotary mould. It provides several functions without requiring subsequent assembly.
Quels matériaux ont une bonne adhérence l'un sur l'autre lors de la bi-injection ?
The main compatibilities in bi-injection are: PP with TPE-V, PA with TPE-E, ABS with TPU, PC with TPU, PA with polyacetal POM. Chemical compatibility is essential for adhesion. If it is not natural, mechanical retention (grooves, anchor holes) is created between the two materials to ensure holding strength.
Quelle est la différence entre la bi-injection et le surmoulage?
Bi-injection injects two polymers in a single operation on a multi-material press. Overmoulding injects the second polymer onto a first moulded part, which is placed manually or robotically into a new mould. Bi-injection is more productive, while overmoulding is more flexible for small production runs.
How to choose the two materials for a two-material part?
The choice relies on chemical compatibility for adhesion, compatible injection temperatures, similar shrinkage rates to avoid deformation, and the desired final properties (rigid structure with a flexible surface, insulator with conductor, opaque with transparent). A pre-production adhesion test is highly recommended.
Are TPEs (elastomers) compatible with PP in bi-injection?
Yes, TPE-V (thermoplastic vulcanisates based on PP) are designed to bond naturally with PP. Chemical adhesion is excellent without preparation. This is the most commonly used combination for soft grips, integrated seals, and grip zones on large-scale PP structural parts.
Pourquoi associer un thermoplastique rigide et un thermoplastique souple ?
This combination incorporates several functions into a single part: structural rigidity on one side, softness or anti-slip on the other. Frequent applications include: tool handles, housings with integrated seals, toys, and medical devices. Two-shot moulding avoids subsequent assembly, reducing costs and potential product failure points.
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