10.8.1 Multi-Component Injection Moulding

This method describes a process whereby plastics are injected into one mould during a single injection cycle. The most common process in this category is co-injection moulding. Other less common variants are bi-injection and intermittent techniques.

10.8.2 Co-Injection Moulding

Co-injection moulding is a variant of the standard injection process and has been in use since the early 1970s. A number of terminologies are used that can encompass this process such as sandwich moulding, 2K (2-component) or 3K (3-component) and dual-injection or multi-component. For the purpose of this chapter, co-injection moulding is the preferred terminology. This technique offers the advantages of combining two or more material properties to produce a sandwich structure. This is achieved by making sequential injections into the same mould with one material as the core and another as the skin. This is illustrated in Figure 10.2.

Figure 10.2: Encapsulation of core material by skin during co-injection moulding

The result is the distinctive sandwich structure of skin and core as shown in Figure 10.3.

Figure 10.3: Cross-section of sandwich structure of a co-injection moulding

Co-injection moulding offers numerous possibilities in terms of a variety of material combinations, some of which are shown in Table 10.2.