Aspects to pay attention to in precision injection molding

Among the related factors that affect precision injection molding, the mold is the key to obtaining precision plastic products that meet the quality requirements. The mold design and whether the mold design is fair will directly affect the quality of plastic products. Since the mold cavity size is derived from the required size of the plastic product plus the shrinkage rate of the material used, the shrinkage rate is often a value within a range recommended by the plastic manufacturer or engineering plastics manual. It is not only related to the gate of the mold. The situation and the gate position are related to the dispersion, but also related to the crystal orientation (anisotropy) of the engineering plastics, the shape and size of the plastic products, and the distance and position of the gate. The main factors affecting plastic shrinkage include thermal shrinkage, phase change shrinkage, orientation shrinkage, shrinkage shrinkage and elastic recovery, etc. These influencing factors are related to the molding conditions or operating conditions of precision injection molded products. Therefore, mold designers must have rich design and injection molding experience, and must consider the relationship between these influencing factors and injection conditions and their apparent factors, such as injection pressure and cavity pressure and filling speed, injection melt temperature and mold temperature , Mold structure and gate situation and distribution, and the influence of factors such as gate cross-sectional area, product wall thickness, reinforcing filler content in plastic materials, crystallinity and orientation of plastic materials. The influence of the above factors is also different due to different plastic materials, or other molding conditions such as temperature, humidity, continued crystallization, and changes in the injection molding machine after molding.

Because the injection molding process is the process of transforming the plastic from solid (powder or pellets) to liquid (melt) to solid (product). From the pellets to the melt, and then from the melt to the product, the temperature field, the flow field and the density field are in the middle. Under the combined action of these fields, different plastics (thermosetting or thermoplastic, crystalline or non-crystalline, reinforced or non-reinforced, etc.) have different polymer structural morphologies and rheological properties. All the factors that affect the above-mentioned fields will definitely affect the physical and mechanical properties, size, shape, precision and appearance quality of plastic products.

In this way, the internal connection between process factors and polymer properties, structural morphology and plastic products will be expressed through plastic products. A clear analysis of these internal connections is of great significance to the fair formulation of the injection molding process, the fair design and manufacture of molds according to drawings, and the fair selection of injection molding equipment. Precision injection molding is also distinguished from ordinary injection molding in terms of injection pressure and injection rate. Precision injection molding often adopts high-pressure or ultra-high-pressure injection and high-speed injection to obtain a smaller molding shrinkage rate.