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Multi material injection molding is to integrate a variety of plastic materials with different characteristics to improve the added value of goods. This paper mainly introduces the precautions of multi-material injection molding.

An important point of multi-material injection molding is that the quality inspection of the substrate and the covering material should be closely bonded. In order to strengthen the adhesion, the melting temperature of the covering material should be the same as that of the substrate material. When the melting temperature of the covering material is too low, the surface of the substrate cannot melt, and the bonding strength between them is not high. However, if the melting temperature is too high, the substrate will be deformed. In serious cases, the covering material will penetrate the substrate, resulting in the failure of part processing. Therefore, the selection of matching materials can ensure good bonding effect.

Several matching materials should have similar chemical properties. When the base material does not match the covering material, it can only form mechanical bonding, not chemical bonding. This will cause many materials to fail to bond together.

There are also many problems in multi-material injection molding. The common ones are: insufficient chemical or mechanical bonding strength, incomplete material filling of single or multiple parts, burrs of single or multiple material parts, etc.

The injection machine must maintain the consistency of 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 proportion is very important for all injection molding processes, especially in the secondary injection molding process. The check device can separate the coating material like a sluice. If the materials injected during the second injection are all metal, the check device is easier to operate, but if it is a metal substrate and plastic with greater elasticity, the check device is more difficult to operate.