The main influencing factors of various faults in precision injection molding
Date: October 9, 2024
The basis for determining precision injection molding processing is the accuracy of the injection molded product, namely the dimensional tolerance, geometric tolerance, and surface roughness of the product. There are many related conditions required for precision injection molding, and the most essential ones are plastic materials, injection molds, injection processes, and injection equipment. When designing plastic products, engineering plastic materials should be selected first, and engineering plastics that can be precision injection molded must be selected with high mechanical properties, dimensional stability, good creep resistance, and environmental stress cracking resistance. Secondly, suitable injection molding machines should be selected based on the selected plastic material, finished product size accuracy, part weight, quality requirements, and expected mold structure. The factors that affect precision injection molded products during the processing mainly come from the accuracy of the mold, injection shrinkage, and the amplitude of changes in the environmental temperature and humidity of the product.
precision injection molding
The main influencing factors of various faults in precision injection molding
In precision injection molding, the mold is one of the key factors used to obtain precision plastic products that meet quality requirements. The mold used for precision injection molding should truly meet the requirements of product size, accuracy, and shape. But even if the precision and size of the mold are consistent, the actual size of the molded plastic product will still be inconsistent due to differences in shrinkage. Therefore, effectively controlling the shrinkage rate of plastic products is crucial in precision injection molding technology.
The rationality of mold design directly affects the shrinkage rate of plastic products. The size of the mold cavity is calculated by adding the estimated shrinkage rate to the size of the plastic product, and the shrinkage rate is a value recommended by the plastic manufacturer or engineering plastic manual within a range. It is not only related to the gate form, gate position, and distribution of the mold, but also to the crystal orientation (anisotropy) of the engineering plastic, the shape, size, distance, and position of the plastic product to the gate. The main factors affecting the shrinkage rate of plastics include thermal shrinkage, phase change shrinkage, orientation shrinkage, compression shrinkage, and elastic recovery, which are related to the molding or operating conditions of precision injection molded products. Therefore, when designing molds, it is necessary to consider the relationship between these influencing factors and injection conditions, as well as their apparent factors, such as injection pressure and mold 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 fillers in plastic materials, crystallinity and orientation of plastic materials. The influence of the above factors also varies due to different plastic materials, other molding conditions such as temperature, humidity, continued crystallization, internal stress after molding, and changes in injection molding machines.
Plastic mold manufacturersThe injection molding process is the process of transforming plastic from a solid state (powder or pellet) to a liquid state (melt) and then to a solid state (product). From pellets to melt, and then from melt to product, the process involves the interaction of temperature field, stress field, flow field, and density field. Under the combined action of these fields, different plastics (thermosetting or thermoplastic, crystalline or amorphous, reinforced or non reinforced, etc.) have different polymer structure forms and rheological properties. Any factors that affect the above-mentioned “field” will inevitably affect the physical and mechanical properties, size, shape, accuracy, and appearance quality of plastic products.
In this way, the intrinsic relationship between process factors, polymer properties, structural morphology, and plastic products will be manifested through plastic products. Analyzing these internal connections is of great significance for the rational formulation of injection molding processes, the rational design and manufacture of molds according to drawings, and even the rational selection of injection molding equipment. Precision injection molding differs from regular injection molding in terms of injection pressure and injection rate. High pressure or ultra-high pressure injection, as well as high-speed injection, are commonly used in precision injection molding to achieve smaller molding shrinkage. Taking into account the various reasons mentioned above, when designing precision injection molds, in addition to considering the design elements of general molds, the following points must also be considered: ① adopting appropriate mold size tolerances; ② Prevent errors in molding shrinkage rate; ③ Prevent injection molding deformation; ④ Prevent demolding deformation; ⑤ Minimize mold manufacturing errors; ⑥ Prevent errors in mold accuracy; ⑦ Maintain mold accuracy.