Main factors affecting precision injection mold

The difference between precision injection molding and ordinary injection molding lies in the word "precision", that is, higher requirements on plastic products, smaller tolerance, and more beautiful appearance.
Overview of precision injection molding
Precision injection molding is based on the precision of injection molding products, that is, the dimensional tolerance, geometric tolerance and surface roughness of the products. There must be many related conditions to carry out precision injection molding, and the four basic factors are plastic material, injection mold, injection molding process and injection molding equipment. When designing plastic products, engineering plastics materials should be selected first, and those with high mechanical properties, stable size, good creep resistance and environmental stress cracking resistance must be selected for engineering plastics capable of precision injection molding. Secondly, the appropriate injection molding machine shall be selected according to the selected plastic material, finished product size accuracy, part weight, quality requirements and expected mold structure. In the process of processing, the factors that affect precision injection molding products mainly come from the precision of the mold, the shrinkage of injection molding, and the range of changes in the ambient temperature and humidity of the products.
Influence of mold precision on precision injection molding
In precision injection molding, mold is one of the keys to obtain precision plastic products that meet the quality requirements. The mold used for precision injection molding should meet the requirements of product size, precision and shape. However, even if the precision and size of the mold are consistent, the actual size of the molded plastic products will be inconsistent due to the difference in shrinkage. Therefore, it is very important to effectively control the shrinkage of plastic products in precision injection molding technology.
Factors affecting injection shrinkage
Whether the mold design is reasonable or not will directly affect the shrinkage rate of plastic products. Because the mold cavity size is calculated by the size of plastic products plus the estimated shrinkage rate, and the shrinkage rate is a range of values recommended by the plastic manufacturer or the Engineering Plastics Manual. It is not only related to the mold gate form, gate position and distribution, but also related to the crystalline orientation (anisotropy) of engineering plastics, the shape of plastic products Size, distance to gate and position. The main factors affecting the shrinkage of plastics are heat shrinkage, phase change shrinkage, orientation shrinkage, compression shrinkage and elastic recovery, and these factors are related to the molding conditions or operating conditions of precision injection molding products. Therefore, the relationship between these influencing factors and injection conditions and their apparent factors must be considered when designing the mold, 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 sectional area, product wall thickness, content of reinforcing filler in plastic materials, crystallinity and orientation of plastic materials and other factors. The influence of the above factors is also different due to different plastic materials, other molding conditions such as temperature, humidity, continuous crystallization, internal stress after molding, and changes in injection molding machine.
Influence of ambient temperature and humidity change of products
Because the injection molding process is the process of transforming plastics from solid (powder or granule) to liquid (melt) and then to solid (product). From granular material to melt, and then from melt to product, the process involves temperature field, stress 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 and rheological properties. All factors that affect the above "field" will affect the physical and mechanical properties, size, shape, accuracy and appearance quality of plastic products.
Summary
In this way, the internal relationship between process factors and the performance, structure and morphology of polymers and plastic products will be shown through plastic products. The analysis of these internal links is of great significance to the rational formulation of injection molding process, the rational design and manufacture of molds according to drawings, and even the rational selection of injection molding equipment. Precision injection molding is also different from ordinary injection molding in terms of injection pressure and injection rate. Precision injection molding often uses high-pressure or ultra-high-pressure injection and high-speed injection to obtain small molding shrinkage. Based on the above reasons, in addition to the design elements of the general mold, the following points must be considered when designing the precision injection mold: ① adopting appropriate mold size tolerance; ② Prevent forming shrinkage error; ③ Prevent injection molding deformation; ④ Prevent demoulding deformation; ⑤ Minimize mold manufacturing error; ⑥ Prevent mold precision error; ⑦ Maintain mold accuracy.