Mold designers must have a wealth of design and injection molding experience, must consider the relationship between these influencing factors and injection molding conditions and its apparent factors, such as injection pressure and cavity pressure and filling speed, injection melt temperature and mold temperature, mold The structure and the form and distribution of the gate, as well as the cross-sectional area of the gate, the wall thickness of the product, the content of the reinforcing filler in the plastic material, the crystallinity and orientation of the plastic material, and the like. The influence of the above factors also differs depending on the plastic material or other molding conditions such as temperature, humidity, continued crystallization, and changes in the injection molding machine after molding.
Among the factors affecting precision injection molding, molds are the key to obtaining precision plastic products that meet quality requirements. The design of the mold, 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 of the material used, the shrinkage rate is often a value within the range recommended by the plastics manufacturer or engineering plastics manual, not only with the gate form of the mold. The position of the gate is related to the distribution, and is related to the crystal orientation (anisotropic) of the engineering plastic, the shape and size of the plastic product, and the distance and position of the gate. The main factors affecting the shrinkage of plastics include heat shrinkage, phase change shrinkage, orientation shrinkage, compression shrinkage and elastic recovery, which are related to the molding conditions or operating conditions of precision injection molded articles.
Because the injection molding process is the process of converting plastic from solid (powder or pellet) to liquid (melt) to solid (product). From the pellet to the melt, and then from the melt to the product, the temperature field, flow field and density field are used. Under the combined action of these fields, different plastics (thermoset or thermoplastic, crystalline or amorphous, reinforced or unreinforced, etc.) have different polymer morphological and rheological properties. Any factors that affect the above-mentioned "field" will affect the physical and mechanical properties, size, shape, precision and appearance quality of plastic products.
Thus, the intrinsic link between process factors and polymer properties, structural morphology, and plastics is manifested by plastics. Analysis of these intrinsic links is of great significance for the rational preparation of injection molding process, rational design and manufacturing of molds according to drawings, and even the selection of injection molding equipment. Precision injection molding and ordinary injection molding also differ in injection pressure and injection rate. Precision injection molding often uses high pressure or ultra high pressure injection and high speed injection to obtain a small molding shrinkage.