Precision injection molding molds are different from ordinary injection molding processes in the word "precision", that is, higher requirements, smaller tolerances, and more beautiful appearance on injection molded products. What are the main factors affecting precision injection molding with you today?
Precision injection molding is based on the precision of injection molded products, that is, the dimensional tolerance, geometric tolerance and surface roughness of the product. To perform precision injection molding, there must be many related conditions, and the most essential are the four basic factors of plastic material, injection mold, injection molding process and injection molding equipment. When designing plastic products, engineering plastic materials should be selected first, and engineering plastics capable of precision injection molding must choose those materials with high mechanical properties, dimensional stability, good creep resistance, and environmental stress crack resistance. Secondly, the appropriate injection molding machine should be selected according to the selected plastic material, finished product dimensional accuracy, piece weight, quality requirements and the expected mold structure. In the process of processing, the factors that affect the precision injection molding products mainly come from the precision of the mold, the injection shrinkage, and the changes in the ambient temperature and humidity of the product.
In precision injection molding, the mold is one of the keys to obtain precision plastic products that meet the quality requirements. The precision injection mold should meet the requirements of product size, accuracy and shape. However, even if the precision and size of the mold are the same, the actual size of the molded plastic product will be inconsistent due to the difference in shrinkage. Therefore, it is very important to effectively control the shrinkage rate of plastic products in precision injection molding technology.
Whether the design of injection mold components is reasonable or not will directly affect the shrinkage rate of plastic products, because the size of the mold cavity is obtained from the size of the plastic product plus the estimated shrinkage rate, and the shrinkage rate is determined by the plastic manufacturer or engineering plastics. The value within a range recommended by the manual is not only related to the gate form, gate location and distribution of the mold, but also to the crystal orientation (anisotropy) of engineering plastics, the shape and size of plastic products, and the distance to the gate. distance and location. The main factors affecting the plastic shrinkage are thermal shrinkage, phase change shrinkage, orientation shrinkage, compression shrinkage and elastic recovery, and these influencing factors are related to the molding conditions or operating conditions of precision injection molding products. Therefore, the relationship between these influencing factors and injection conditions and their apparent factors must be considered when designing the mold, such as injection pressure and cavity pressure and filling speed, injection melt temperature and mold temperature, mold structure and gate form and distribution. , and the influence of gate cross-sectional area, product wall thickness, content of reinforcing fillers in plastic materials, crystallinity and orientation of plastic materials and other factors.
Because the injection molding process is a process of converting plastic from solid to liquid and back to solid. From the pellets to the melt, and then from the melt to the product, the temperature field, stress field, flow field and density field are involved in the middle. Under the combined action of these fields, different plastics have different polymer structures. and rheological properties. All factors that affect the above "field" will definitely affect the physical and mechanical properties, size, shape, precision and appearance quality of plastic products.
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