Plastic Injection Molds

Injection Molds: Understanding How a Mold is Built

Molds, or tools, are rendered in specialized 3D software, and consist of two halves, generally called “Half A” and “Half B”. Where the two halves come together and separate is called the “Draw” and this forms the “Parting Line”.

Most injection molds are constructed from steel as steel is strong enough to allow for a long tool life. Generally, millions of injection molded parts can be manufactured from a single steel mold before the mold must be serviced or remade. These molds are manufactured using a computer numerical control, or CNC machine, which helps to control tolerances and reduce the lead time of building the mold. The cost of producing steel tools varies based on the size and complexity of the final part being produced. Depending on the size of the part, it is possible to produce multiple parts from the same tool in a single “hit” through a process called “nesting”.

In some cases, molds will be constructed using a more cost-effective material, such as aluminum, however the trade-off for using a material other than steel is the life of the mold will not be as long and less parts will be able to be produced.

Using our design software, Nelson-Miller will design your tool to allow for maximum efficiency and material optimization.

Shown here is one half of a plastic mold with the plastic injection nozzle highlighted in the background.

Continue learning about Nelson-Miller’s plastic injection molding process including selecting the right material, building a mold, features, and important specifications.

How Are Plastic Injection Molds Made?