Insert Molding is a process that will enable components such as terminals, pins, studs, and fasteners, to be molded into a part. Insert molding allows the design engineer options he or she may not have thought possible.
It is not as common as you might think and it takes carefull attention to detail when attempting to accomplish this process. A more common approach might be to heat stake or ultra sonic weld the inserts into the plastic parts but this requires an extra step which usually means added cost.
If you are designing a device or an enclosure that requires inserts to be added for functional or assembly reasons you will need to look at your options carefully to determine which approach is best.