The designer of the mold must have extensive design and injection molding experience.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 influence of gate cross-sectional area, product wall thickness, content of reinforcing filler 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.
Among the related factors that affect precision injection molding, the mold is the key to obtain precision plastic products that meet the quality requirements. 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, 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 form The gate position is related to the distribution, but also to the crystal orientation of engineering plastics, the shape and size of plastic products and the distance and position from the gate. The main factors affecting the shrinkage of plastics include heat 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.
Because the injection molding process is the process of changing the plastic from solid to liquid and solid. From the pellet to the melt, and then from the melt to the product, the temperature field, flow field and density field are required to pass through. Under the joint action of these fields, different plastics have different polymer structural 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 the injection molding process, reasonably design and manufacture molds according to the drawings, and even choose the injection molding equipment reasonably. 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.