Overview of Multi-Material Molding


MMM actually encompasses a wide range of processes, all capable of producing different types of MMO's. However, in general, MMM is a more advanced variation of SMM capable of producing objects with two or more different polymeric materials. The following tree relates some of the more common MMM processes.
Multi-component molding is perhaps the simplest and most common form of MMM. It involves the simultaneous (or sometimes sequential) injection of two different materials through either the same or different gate locations in a single mold. Multi-shot (or "multi-stage") molding is the most complex and versatile of the MMM process. It involves injecting the different materials into the mold in a specified sequence, where the mold cavity geometry may partially or completely change between sequences. Over-molding and insert molding simply involve molding a resin around a preformed part; either metal (as in insert molding), or a previously-made injection-molded plastic part (as in over-molding). Each of the three classes of MMM are considerably different. Each specific MMM process requires its own set of specialized equipment; however, there are certain equipment requirements that are generally the same for all types of MMM. This is discussed below.


General Multi-Material Molding Equipment

As with SMM, all MMM machines have at least one injection unit, a clamp, and a mold. Unlike SMM, all MMM machines must have a separate material-feed system for each material used. Additionally, with the exception of some multi-component processes, all MMM machines must have a separate injection unit for each material. Furthermore, the machine controller must be capable of controlling multiple separate injection sequences. Because two or more injection units are usually necessary, molders have many options in locating the separate injection units within the machine. There are many options, each with their own advantages, disadvantages, and capabilities. Some common injection unit configurations are schematically illustrated in Figure 1.

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As far as the clamping unit goes, no special equipment is usually required for MMM. That is, standard hydraulic or mechanical clamping units can be utilized, provided they provide enough clamping force. Thus, the key equipment differences between SMM and MMM lie in the molds. Each process uses some modified form of the standard injection mold.