Molds are built through two main methods: standard machining and EDM. Standard machining, in its conventional form, has historically been the method of building injection molds. With technological development, CNC machining became the predominant means of making more complex injection molding with more accurate mold details in less time than traditional methods.

More complex parts are formed using more complex molds. These may have sections called slides, that move into a cavity perpendicular to the draw direction, to form overhanging part features. When the mold is opened, the slides are pulled away from the plastic part by using stationary “angle pins” on the stationary mold half. These pins enter a slot in the slides and cause the slides to move backward when the moving half of the mold opens. The part is then ejected and the mold closes. The closing action of the injection molding causes the slides to move forward along the angle pins

As the granules are slowly moved forward by a screw-type plunger, the plastic is forced into a heated chamber, where it is melted. As the plunger advances, the melted plastic is forced through a nozzle that rests against the mold, allowing it to enter the mold cavity through a gate and runner system.