The mold designer must have rich design and injection molding experience. For precision mold processing, the relationship between these influencing factors and the injection conditions and their apparent factors must be considered, 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 gate cross-sectional area, product wall thickness, the content of reinforcing filler in plastic materials, the crystallinity and orientation of plastic materials and other factors. 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.
Among the relevant factors that affect precision injection molding, molds are the key to obtaining precision plastic products that meet quality requirements. Mold design, whether the mold design is reasonable will directly affect the quality of plastic products. Because the mold cavity size is derived from the required size of the plastic product plus the shrinkage rate of the material used, and 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 mold gate The gate position is related to the distribution, and it is related to the crystal orientation (anisotropy) of engineering plastics, the shape and size of the plastic products to 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, etc., and these influence factors are related to the molding conditions or operating conditions of precision injection molded products.
Because the injection molding process is the process of changing plastics from solid (powder or pellet) to liquid (melt) to solid (product). Precision mold processing, from pellets to melt, and then from melt to product, through the temperature field, flow field and density field. Under the joint action of these fields, different plastics (thermosetting or thermoplastic, crystalline or non-crystalline, reinforced or non-reinforced, etc.) have different polymer structure morphology and rheological properties. All factors that affect the above-mentioned “field” will definitely affect the physical and mechanical properties, size, shape, accuracy and appearance quality of plastic products.
In this way, the inherent relationship between process factors and polymer properties, structural morphology and plastic products will be expressed through plastic products. It is of great significance to analyze these intrinsic connections to reasonably formulate injection molding processing technology, rationally design and manufacture molds according to drawings, and even rationally select injection molding processing equipment. Precision injection molding and ordinary injection molding also have differences 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 rate.