Injection molds are a complex system that must meet many of the requirements of the injection molding process. The primary function of the mold is to hold the polymer melt in the mold cavity so that the open cavity can be filled to form a plastic part with a shape that is consistent with the open cavity of the mold; secondly, it is effective to transfer heat from the hot polymer melt to the cold On the mold steel, the injection molded article is made as uniform and economical as possible; the third main function of the mold is to take the article out of the mold in a quick and repeatable manner so that subsequent molding can be carried out efficiently.

These three main kinetic energy - melting, heat transfer and removal of the product - also include secondary requirements for injection molds. Figure 1.3 provides a partial hierarchy of injection mold functions. For example, the functional requirements for including the melt in the mold:

Molds must be able to withstand large forces that tend to open or deform the mold.

The mold is to include a casting system for connecting the nozzle of the injection molding machine to the cavity of the mold for transfer of the polymer melt.

These secondary functions may also cause third-level functions that depend on specific mold components.

It should be recognized that Figure 1.3 does not fully list all the functions of the injection mold. Only a few of the primary and secondary functions are listed. These functions must be considered in the engineering of the injection mold. Even so, a skilled design engineer may realize that conflicting requirements in mold design can be met by a variety of functions.

For example, effective cooling can be achieved by using a plurality of closely spaced cooling passages that conform to the mold cavity. However, in order to eject the article, multiple pushers may be required at a particular location, and these locations may conflict with the cooling channels. At this point, the mold design engineer should consider the relative importance between the conflicting requirements, and the result can be a satisfactory mold design. When in doubt, novice design engineers tend to be redundant. This tendency should be avoided as it can lead to large, expensive and inefficient molds.