What are the requirements for injection mold design?

Author: MULAN -Plastic Molding Manufacturer

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 mold cavity when it is cooled and solidified. 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 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 cooling and solidification process The shrinkage of plastic is very complicated. The shrinkage rate of plastic in each part of the cavity is different in each direction. The shrinkage rate of plastic of different types and grades is very different. When the resin or plastic of the same grade is processed, due to the different formula Sex and shrinkage are also different. Based on the above characteristics, when designing an injection mold, it is necessary to fully understand the characteristics of the processed plastic raw materials, so that the designed injection mold can be used reasonably, and the characteristics of the plastic can 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 plastic parts determines the complexity of the structure of the injection mold, and the technical requirements of plastic parts (dimensional accuracy, surface roughness, etc.) determine the difficulty of the injection mold manufacturing and molding process. Therefore, for those that do not meet the special requirements of plastic injection molding, unreasonable structural shapes, etc., an improved design plan for injection molded parts should be proposed, otherwise it will increase the difficulty of injection mold design and manufacturing and injection molding process. 2. Familiar with the technical specifications of the injection molding machine 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 plastic molds, including the flow position of the plastic melt, the larger flow distance ratio that the melt can achieve: analyze the flow resistance of the runner and cavity, and the original air in the cavity Discharge, crystallization that may occur in the injection mold, orientation and internal stress caused by it, cooling shrinkage and compensation of the plastic, requirements of the plastic on the temperature of the injection mold, etc. 4. Considering the design and manufacture of injection molds, the following problems are mainly solved: ① The structure of injection molds should be reasonably selected. According to the drawings and technical requirements of plastic parts, research and select appropriate molding methods and equipment, combine the factory's mechanical processing capabilities, propose injection mold structure plans, fully solicit opinions from relevant parties, conduct analysis and discussion, so as to design injection mold structures Reasonable, reliable, easy to operate.

If necessary, according to the needs of injection mold design and processing, the request to modify the drawings of plastic parts can be put forward, but it can only be implemented after obtaining the consent of the user. ②The size of injection molded parts should be calculated correctly. Molded parts are the direct factors to determine the shape, size and surface quality of plastic parts, which have a lot to do with each other and require special attention.

When calculating the size of molded parts, the average shrinkage method can generally be used. For plastic parts with high precision and need to control the mold repair allowance, 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 geometric shape of the plastic part in different directions. Make up for the influence of certain factors that are difficult to consider in theory. ③The 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 to manufacture. Especially for those more complex formed parts, it must be considered whether to use general machining 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 solved when designing the injection mold, and at the same time, the mold repair after the trial mold should be considered, and sufficient mold repair allowance should be left.

④The designed injection mold should be efficient, safe and reliable. This requirement involves many aspects of injection mold design, such as filling of the pouring system, closed modules, good temperature adjustment, and flexible and reliable demoulding mechanism. ⑤Injection 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 necessary requirements be put forward for their materials, processing methods, heat treatment, etc., but pins 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. ⑥The structure of the injection mold should adapt to the molding characteristics of the plastic.

When designing an injection mold, one 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.