The term “multi-component” here refers to the several different plastics which are  injected into the injection mould. For a two-component injection mould, which specialists refer to as a 2-C mould, this means that two different plastics are injected  one after another into the injection mould. This method is becoming more and more important. The demand for getting a  ready-to-use piece from an injection mould is steadily increasing. More and more  companies are upgrading their injection mould technology as well as machining  techniques. The areas of application for plastic parts are multiplying through this  method.

1 Material Pairings 

The plastic parts that are used for this method have different characteristics. For example they can be hard or soft. For a housing made of hard plastic, a soft  rubber sealing is injected in the second process step. For this pairing the hard and  the soft plastic must permanently bond.

Another common pairing is the same material but in different colours. For example, a common application is vehicle rear lights in several colours. For these types  of applications 3-C or 4-C moulds are not uncommon any more. In the brush head of an electric toothbrush different hard-hard pairings are processed. Here no bonding of the materials is needed but one of the plastics has  sliding properties so the brush can move.

2 Mould Technology 

The mould technology is a significant improvement compared to the mould types  described so far. We are talking about very complex and expensive moulds. 

2.1 Shifting Technology 

For these types of moulds the simplest method is shifting. For this procedure a  2-C mould has two cavities, and a multi-component mould has an even number of  cavities. The first material is injected in half of the cavities and the second material is  injected in the other half. The mould cavities are arranged in the injection mould  so the handling system or robot can shift the pieces from the first half to the second  half. The pieces are therefore evenly distributed, either linearly or in a circle. Our example is a mould in which a coaster is injected with hard/white–soft/blue  material pairing. In the first mould cavity the blank for the coaster made of hard  material is injection moulded. In this first injection, the area which is to be filled  with the soft material in the second injection process is left as a recess. All recessed  areas are connected together so that one feed point suffices for the soft material.  After the mould is opened, the semi-finished part from the first half is transported  to the second half where the coaster is finished. For every cycle there is one half with semi-finished and one half with finished  parts. The number of pieces that come out of the machine is therefore always half  of the number of cavities. Thus two cavities corresponds to one finished piece,  four cavities corresponds to two finished pieces, and so on. Two injection units are  required to inject all mould cavities simultaneously. The coaster is displayed in Figure 2.28, as it comes out of the mould as semifinished (after the first injection process) and as finished part.