Precautions for Multi-material Injection Molding

Author: MULAN – Plastic Molding Manufacturer

Multi-material injection molding is the fusion of a variety of plastic materials with different characteristics to increase the added value of products. This article mainly introduces the precautions for multi-material injection molding processing. It is very important for multi-material injection molding that the adhesion between the base material and the covering material quality inspection should be tight. To strengthen the adhesion, the melting temperature of the covering material should be the same as that 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 covering material will penetrate the substrate, resulting in the failure of the part to be processed. Therefore, the selection of matching materials can ensure a good bonding effect.

Several matching materials should have similar chemical properties. When the base material and cover material do not match, generally only a mechanical bond can be formed, not a chemical bond. This can prevent multiple materials from bonding together.

Multi-material injection molding also has many problems, the more common ones include: insufficient chemical or mechanical bond strength, incomplete material filling of single or multiple parts, and burrs of single or multiple material parts. Injection machines must maintain consistent injections. In addition, the injection volume of the injection equipment barrel and the size ratio of the molded parts are also important factors affecting the quality of injection molding.

This ratio is very important for all injection molding processes, but especially in overmolding processes. The backstop can separate the coating materials like a water gate. When the secondary injection material is all metal, the backstop is easier to operate. If it is a metal substrate and more elastic plastic, the backstop is more difficult to operate.