Analysis of Factors Affecting Precision Injection Molding

2021-03-23 10:55:56 admin

Analysis of Factors Affecting Precision Injection Molding




Precision injection molding will be affected by many related factors and environmental conditions, and the most basic are the basic factors of plastic materials, injection molds, injection molding processes and injection molding equipment. In the early stage of designing plastic products, first select engineering plastics that can be needed according to the environment. Secondly, the selected plastic material, finished product dimensional accuracy, part weight, quality requirements and expected mold structure are used to select the appropriate injection molding machine.


Among the related factors that affect precision injection molding, molds are the key to obtaining precision plastic products that meet quality requirements. The design of the mold and whether the mold design is reasonable will directly affect the quality of plastic products.


Since the mold cavity size is derived from the required size of the plastic product plus the shrinkage rate of the material used, the shrinkage rate is often a value within a range recommended by the plastic manufacturer or engineering plastics manual. It is not only related to the mold gate type , The gate position is related to the distribution, and is related to the crystal orientation (anisotropy) of engineering plastics, the shape and size of the plastic product, and the distance and location from the gate.


The main factors affecting plastic shrinkage include thermal shrinkage, phase change shrinkage, orientation shrinkage, compression shrinkage and elastic recovery, etc. These influencing factors are related to the molding conditions or operating conditions of precision injection molded products.


Therefore, mold designers must have rich design and injection molding experience, and must consider the relationship between these influencing factors and injection conditions and their apparent 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 the influence of factors such as gate cross-sectional area, product wall thickness, reinforcing filler content in plastic materials, crystallinity and orientation of plastic materials.


The influence of the above factors is also different due to different plastic materials, or other molding conditions such as temperature, humidity, continued crystallization, and changes in the injection molding machine after molding.


Because the injection molding process is a process of transforming plastics from solid (powder or pellets) to liquid (melt) to solid (product). From the pellets to the melt, and then from the melt to the product, the temperature field, flow field and density field must be affected in the middle. Under the combined action of these fields, different plastics (thermosetting or thermoplastic, crystalline or non-crystalline, reinforced or non-reinforced, etc.) have different polymer structural morphologies and rheological properties.


All the factors that affect the above-mentioned "field" will definitely affect the physical and mechanical properties, size, shape, precision and appearance quality of plastic products.


In this way, the internal connection between process factors and polymer properties, structural morphology and plastic products will be manifested through plastic products. A clear analysis of these internal connections is of great significance to rationally formulating the injection molding process, rationally designing and manufacturing molds according to drawings, and even rationally selecting injection molding equipment.


Precision injection molding and ordinary injection molding are also different in injection pressure and injection rate. Precision injection molding often uses high-pressure or ultra-high-pressure injection and high-speed injection to obtain a smaller mold shrinkage rate.