Insert molding uses the same materials as the injection molding process. For extreme, high heat - engineered thermoplastics are used. These materials withstand very high temperatures and the components can withstand very harsh environments because of the physical, electrical and chemical properties.
The insert is placed in the mold - either by hand, or by automation before the material is injected into the mold. Then, as the material flows into undercut features in the insert, the insert is anchored much more securely than if it were assembled to a previously molded component.
Some injection molding manufacturers utilize vertical/vertical injection molding presses which use gravity to aid in the insert molding process by keeping the insert in position during mold closing.
Most vertical presses have a feature that utilizes multiple bottom mold halves to be used with one top. While one bottom half is molding with the top half, the other bottom is available to be loaded with the insert.
Since multiple bottom halves allow inserts to be loaded in one bottom while others are molding, press time is reduced.