2K injection moulding

Two-Component Injection Moulding: Everything you need to know about Bi-injection

Thetwo-component plastic injection, also called bi-injection Overmoulding, or multi-material moulding, is a cutting-edge manufacturing process that allows for the combination of two different materials (often of distinct colours or textures) in a single production cycle.

Whether it's to improve product ergonomics, ensure waterproofing, or reduce assembly costs, this technology is revolutionising the Design of complex plastic parts.

What is the bi-injection process?

The principle relies on the use of an injection moulding machine equipped with two distinct injection units. The process generally takes place in two stages within the same rotary or transfer mould:

1. First material injection (often a rigid structure).

2. Mold rotation or part transfer.

3. Injection of the second material (often a flexible elastomer or a second colour) onto the first part.

Thanks to a chemical or mechanical bond between the two polymers, a perfectly integral finished part is obtained at the machine's output.

The Advantages of Two-Component Injection

The use of bi-injection offers strategic benefits both in terms of design and industrial profitability.

1. Time Saving and Productivity

By producing a complex part in a single cycle, you eliminate the steps of post-assembly, by collage or welding. This drastically reduces manufacturing times and the risk of human error.

2. Improved Design and Ergonomics

Bi-material allows for the creation of «Soft Touch» products, highly valued in tools or electronics. It also offers great aesthetic freedom by playing with contrasts of colours and transparencies.

3. Watertightness and Technical Properties

The adhesion between the two materials guarantees a Perfect sealing Without the addition of a gasket. This is the ideal solution for electrical connectors or medical devices.

4. Reduction of Logistics Costs

Fewer components to stock and less handling mean a simplified supply chain and often a more competitive total cost per part in large series.

Disadvantages and Limitations of the Process

Despite its advantages, twin-shot injection imposes certain technical and financial constraints that must be anticipated.

• High initial cost: The investment in a two-component mould and a specialised press is significantly higher than for a conventional single-component injection.

• Material compatibility Not all plastics fuse together. It is crucial to check chemical compatibility to ensure a robust bond. We offer you a selection tool for materials compatible in bi-injection

• Design complexity: The mould design demands in-depth expertise in mechanics and rheology to prevent surface defects or filling issues.

• Production volume Due to tooling costs, this process is primarily profitable for the Medium and large series.

Comparison: Two-shot injection vs Traditional overmoulding

Why choose two-shot injection moulding for your projects?

Bi-material injection is the solution of choice for demanding industries such as’car, the Medical, the’Household appliances and the Home automation. It allows us to meet complex specifications while guaranteeing a high-end finish.

Expert tip: To ensure your project's success, the study of The compatibility between your base polymer (e.g. PP, ABS, PC) and your second material (e.g. TPE, TPU) is the most critical step.