Most of the plastic parts of automobiles are injection molded, because these plastic parts themselves have high design accuracy. The accuracy of the injection molded products, that is, the dimensional tolerance, shape tolerance and surface roughness of the product. There are many relevant conditions for precision injection molding, and the most essential are the four basic factors of plastic materials, injection molds, injection molding process and injection equipment.
When designing plastic products, engineering plastic materials should be selected first, and engineering plastics capable of precision injection molding must select materials with high mechanical properties, stable dimensions, good creep resistance, and resistance to environmental stress cracking.
Secondly, the appropriate injection molding machine should be selected according to the selected plastic material, finished product dimensional accuracy, part weight, quality requirements and the expected mold structure. In the processing process, the factors that affect precision injection molded products mainly come from the precision of the mold, the shrinkage of the injection molding, and the changes in the ambient temperature and humidity of the product.
The main factors affecting the shrinkage rate of plastics are heat shrinkage, phase change shrinkage, orientation shrinkage, compression shrinkage and elastic recovery. These influencing factors are related to the molding conditions or operating conditions of precision injection molded products.
The injection molding process is the process of transforming plastics from solid powders or pellets to liquid melts to solid products. From the pellet to the melt, and then from the melt to the product, the temperature field, the stress field, the flow field, and the density field are required to pass through. Under the joint action of these fields, different plastics are thermosetting or thermoplastic, crystalline or Non-crystalline, reinforced or non-reinforced, etc. have different polymer structure morphology and rheological properties. All factors that affect the above-mentioned fields will definitely affect the physical and mechanical properties, dimensions, shape, accuracy and appearance quality of plastic products.