Mold design

Whether the mold design is reasonable 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. , The gate position is related to the distribution, but also related to the crystal orientation (anisotropy) of engineering plastics, the shape and size of the plastic product, and the distance and location from the gate. The main factors affecting plastic shrinkage include thermal shrinkage, phase change shrinkage, orientation shrinkage, compression 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 form and distribution, as well as 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, internal stress after molding, and changes in injection molding machines. (Guide: The innovation and development of mold technology put forward higher requirements for machine tools)

Because the injection molding process is a process that transforms the plastic from solid (powder or pellets) to liquid (melt) to solid (product). From the pellet to the melt, and then from the melt to the product, the temperature field, the stress 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.

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