The main factors affecting precision injection molding

The precision injection molding is determined on the basis of the precision of the injection molding product, i.e. the dimensional tolerance, position tolerance and surface roughness of the product. There must be many related conditions for precision injection molding, and the most essential are the four basic factors of plastic materials, injection molding molds, injection molding process and injection molding equipment. When designing plastic products, engineering plastic materials should be selected first, and engineering plastics that can be precision injection molding must be selected with those materials with high mechanical properties, stable size, good anti-creep properties and good resistance to environmental stress cracking. Secondly, according to the selected plastic material, finished product size accuracy, part weight, quality requirements and the expected mold structure to choose the applicable injection molding machine. In the process of processing, the factors affecting precision injection molding products mainly come from the accuracy of molds, injection shrinkage, as well as the ambient temperature and humidity of products and other aspects of change.
In precision injection molding, mold is one of the keys to obtain precision plastic products that meet the quality requirements, and molds used for precision injection molding should meet the requirements of product size, precision and shape. However, even if the accuracy and size of the mold are the same, 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 rate of plastic products in precision injection molding technology.
The reasonable design of the mold will directly affect the shrinkage of plastic products, because the mold cavity size is obtained by the size of plastic products plus the estimated shrinkage, and the shrinkage rate is recommended by the plastic manufacturer or engineering plastic manual within a range of values, it is not only related to the mold gate form, gate position and distribution, but also with the crystallization orientation of engineering plastics.
The shape, size, distance to the gate and location of the plastic product are related. The main factors affecting plastic shrinkage are thermal shrinkage, phase contraction, orientation contraction, compression contraction and elastic response, which are related to the molding conditions or operating conditions of precision injection molding products. Therefore, in the design of the mold must consider the relationship between these factors and injection molding conditions and its appearance factors, 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 gate cut-off area, product wall thickness, plastic material to enhance the content of fillers, plastic material crystallization and orientation and other factors. The influence of the above factors also varies according to the different plastic materials, other molding conditions such as temperature, humidity, continued crystallization, internal stress after molding, and changes in injection molding machines.
Because the injection molding process is the process of transforming plastic from solid powder or thyme to liquid melt and into solid product. From the particle to the melt, and then from the melt to the product, the middle to pass through the temperature field, stress field, flow field and density field, etc. , under the joint action of these field, different plastic thermososterstic or thermoplastic, crystalline or non-crystalline, enhanced or non-enhanced, etc. have different polymer structure form and fluidization properties. Any factors that affect the above field will certainly affect the physical and physical properties, size, shape, precision and appearance quality of plastic products. In this way, the intrinsic relationship between process factors and polymer performance, structural form and plastic products is expressed through plastic products. It is of great significance to analyze these internal links, to draw up the injection molding process reasonably, to design and manufacture molds according to drawings, and even to choose the injection molding processing equipment reasonably. Precision injection molding is also different from ordinary injection molding in injection pressure and injection rate, precision injection molding often uses high-pressure or ultra-high-pressure injection, high-speed injection to obtain a smaller molding shrinkage. In addition to considering the design elements of the general mold, the following points should be considered when designing precision injection molds: (1) using appropriate mold size tolerances;