The bi-material injection mould (or bi-injection mould) functions in the same basic way as a single-material injection mould, with the same injection, cooling and ejection functions. 

The main difference is that it is divided into 2 stations, each dedicated to a particular material 

Depending on the product to manufacture and the injection moulding machine, several types of 2K injection moulds are possible : 

• 2K rotary mould 
• 2K index plate mould 
• 2K transfer mould 
• Core back mould 

The design of a bi-material plastic part largely follows the same rules as a standard plastic product. 
However, mould technology must be mastered in order to define the areas where the second material (overmoulding) can or cannot be used. In fact, not all processes allow (easily) the presence of the second material on both sides of the part (mainly rotary moulds), or require process-specific adjustments to the shape. 

Materials can be bonded together chemically or mechanically. It all depends on the nature of the materials. For an initial indication, we invite you to take a look at our 2K material compatibility chart

1. bi material injection moulding allows to combine advantages of both materials into a unique component (hard + soft / different colors / different materials....). 
2. Economically, bi-injection reduces the number of manufacturing stages and therefore the unit cost of a product. 
3. Allows the use of recycled material (hidden under a virgin material for example) 
4. Reduced carbon footprint compared to production of 2 seperate parts assembled together