Multi-material injection molding (MMM) is the process of molding two or more different materials into one plastic part at one time. As is the case in traditional injection molding, multi material injection molding uses materials that are at or near their melting point so that the semi-liquidous (viscous) material can fill voids and cavities within a pre-machined mold, thus taking on the desired shape of designed tooling. In general, advantages of MMM over other production techniques include, but are not limited to, creating parts that have an elastic modulus that varies with location on the part (different regional polymer hardness), creating a single-structure part with different regional materials (similar to the previous advantage, but more focused on joining different types of polymers like rubber and plastic), and also creating a single part with multiple independent polymer colors. Applications range from simple household items like a toothbrush to more heavy duty construction of items like power tools.
The three most widely used methods of MMM fabrication are:
Each MMM primary subset can also be further subdivided into secondary and tertiary subsets, and even further in some cases. This can be advantageous when fine tuning or other general calibration of a specific MMM process is desired. Each primary subset is outlined further in the following sections.