There are following effects or superior utility in the insert molding or molding of plastic-metal composite parts.

1. Combination of plastic characteristics( Easy to fabricate,Less expensive to make complicated shape, Self lubrication, Light in weight, Colourfull, Rustfree and Insulation) and metal characteristic ( High strength, High rigidity and Good conductivity) multiply the function and performance of the combined parts.
2. The value of the molded parts are added by insert-molding.
   For example: Hard parts are inserted to mold by elastomer or rubber on it to improve the touch-feeling. Sink mark on the thick parts is eliminated by insert- molding to improve the appearance.
3. The productivity of assembling the product is improved by using combined parts. Insert-molding is used as pre-assembling process before final assembly.
   For example, it is difficult to handle and put a elastic gasket in place in assembly because it is flexible and deforming. On the other hand it is easy to form a elastic gasket in place by injection molding.
   This process is called MIPG (Molded-in placed gasket) which is a typical pre-assembly.
4. Stock control in a assembly line is easy by decreasing the number of parts. In some cases the part is made by insert molding in a assembly line, in which the stability, consistency and re-producibility of molding process is naturally required.
5. More compact,intricate and precision parts can be made by insert molding, in comparison with post-pressed assembling.
6. More reliable parts can be made by insert molding, because the fastening of plastic and metal is secured and positioning of metal part on plastic part is secured.
7. Limitation of insert molding

1. In some cases, accuracy of dimension of the insert-molded parts is not good than the solid parts, because of;variation of inserted metal parts, spring back of the inserted metal parts, clearance between the mold inserting recess and the metal part, dis-location of inserted parts by the material flow in the mold.
2. In some cases, molding cycle time becomes longer. In the case trade-off between longer time of insert molding and shorter time of assembly should be considered.
3. Additional equipments (parts orientation, escapement and feeder) are needed for automatic operation.
   Anyway there are many advantages and a few disadvantages in insert molding.
   Consider the trade-off of them.