Multi-material injection molding is the fusion of various plastic materials with different characteristics to increase the added value of goods.

It is very important for multi-material injection molding that the adhesion between the base material and the covering material should be tight. To strengthen the adhesion, the melting temperature of the covering material should be the same as the melting temperature of the base material. When the melting temperature of the covering material is too low, the surface of the substrate cannot be melted, and the bonding strength between the two is not high. However, if the melting temperature is too high, the substrate will be deformed, and in severe cases, the cover material will penetrate the substrate, causing the part to fail. Therefore, the selection of matching materials can ensure a good bonding effect.

Several materials that are matched should have similar chemical properties. When the substrate and cover material do not match, generally only mechanical bonds, not chemical bonds, can be formed. This can prevent multiple materials from sticking together.

There are also many problems with multi-material injection molding, the more common of which include: insufficient chemical or mechanical bond strength, incomplete material filling of single or multiple parts, and flashing of single or multiple material parts.

The injection machine must maintain the consistency of the injection. In addition, the injection volume of the injection equipment barrel and the size ratio of the molded parts are also important factors affecting the injection quality. This ratio is very important for all injection molding processes, especially in overmolding. The backstop can separate the film material like a sluice. When the material for the secondary injection is all metal, the backstop is easier to operate. If it is a metal base material and a more elastic plastic, the backstop is more difficult to operate.