The characteristics of the injection mold are determined by the characteristics of the raw materials. There are two main points: one is the filling flow characteristics of the plastic melt during injection, and the other is the shrinkage position of the plastic in the cavity during cooling and solidification. These two points determine the injection mold. Particularity and difficulty of injection mold design. Since the plastic melt is a viscoelastic body, the viscosity of the melt changes with the shear stress and the shear rate when the melt flows. During the flow process, the macromolecules are oriented along the flow direction. After the cavity is filled, the melt is partially compressed, and the process is cooled and solidified. The shrinkage of plastics is very complicated. The shrinkage rates of plastics in various parts and directions in the mold cavity are different. The shrinkage rates of different types and grades of plastics are very different. When the resin or plastic of the same grade is processed, due to the different formulations, its filling flow Sex and shrinkage are also different. Based on the above characteristics, it is necessary to fully understand the characteristics of the processed plastic raw materials when designing the injection mold, so that the designed injection mold can be used rationally, and the characteristics of the plastic should be effectively used in the design process. Therefore, the issues that need to be considered in the injection mold design process are as follows.
1. In-depth analysis of the structure of plastic parts and its technical requirements. The structure of the plastic part determines the complexity of the injection mold structure. The technical requirements of the plastic part (dimensional accuracy, surface roughness, etc.) determine the difficulty of the injection mold manufacturing and molding process, so there is no special requirement for plastic injection molding. , Unreasonable structural shapes, etc., should be proposed to improve the design of injection molded parts, otherwise it will increase the difficulty of injection mold design and manufacturing and injection molding process;
2. Familiar with the technical specifications of injection molding machines. The technical specifications of the injection molding machine restrict the size of the injection mold and the range of injection products that can be molded;
3. Understand the processing performance and process performance of plastics. Including the flow position of the plastic melt, the larger the flow distance ratio that the melt can achieve: analysis of the flow resistance of the runner and the cavity, the original air discharge in the mold cavity, and the possible occurrence of plastic in the injection mold Crystallization, orientation and internal stress caused by it, plastic cooling shrinkage and compensation problems, plastics' requirements for injection mold temperature, etc.;
4. Consider the design and manufacture of injection molds, and mainly solve the following problems:
a. The structure of the injection mold should be selected reasonably. According to the drawings and technical requirements of plastic parts, research and select appropriate molding methods and equipment, combined with the machining capabilities of the factory, propose the injection mold structure plan, fully solicit opinions from relevant parties, conduct analysis and discussion, so as to design the injection mold structure Reasonable, reliable in quality and easy to operate. When necessary, according to the needs of injection mold design and processing, the requirements for modifying the drawings of the plastic parts can be proposed, but it can be implemented after obtaining the user's consent.
b. The dimensions of injection moulded parts should be calculated correctly. Molded parts are the direct factors that determine the shape, size and surface quality of plastic parts, which are closely related and require special attention. When calculating the size of molded parts, generally the average shrinkage method can be used. For plastic parts with high precision and need to control the mold repair margin, it can be calculated according to the tolerance zone method. For large precision plastic parts, try to use the analogy method to calculate the shrinkage rate of the measured plastic part geometry in different directions. Make up for the influence of certain factors that are difficult to consider in theory.
c. The designed injection mold should be easy to manufacture. When designing an injection mold, try to make the designed injection mold easy to manufacture and cheap. Especially for those more complex molded parts, it is necessary to consider whether to use general mechanical processing methods or special processing methods. If a special processing method is used, then how to assemble after processing, similar problems need to be considered and resolved when designing the injection mold, and at the same time, the mold repair after the trial mold should be considered, and sufficient mold repair margin should be left.
d. The designed injection mold should be efficient, safe and reliable. This requirement involves many aspects of injection mold design, such as the gating system needs to be filled, the module is closed, the temperature adjustment Xirong effect is good, and the demolding mechanism is flexible and reliable.
e. The injection mold parts should be wear-resistant and durable. The durability of injection mold parts affects the service life of the entire injection mold. Therefore, when designing such parts, not only should the material, processing method, heat treatment, etc. be required, the pin parts such as push rods are also easy to get stuck. Bending, breaking, and the resulting failures account for most of the injection mold failures. For this reason, how to adjust and replace conveniently should also be considered, but it should be noted that the life of the parts is compatible with the injection mold.
f. The structure of the injection mould should be adapted to the moulding characteristics of the plastic. When designing an injection mold, you should fully understand the molding characteristics of the plastic used and try to meet the requirements, which is also an important measure to obtain high-quality plastic parts.