Analysis of Factors Affecting Mold Precision Injection Molding

Release time:

2022-01-10

Analysis of Factors Affecting Mold Precision Injection Molding

Precision injection molding will be affected by many related factors and environmental conditions, and the basic factors are plastic materials, injection molds, injection molding processes and injection molding equipment. In the early stage of designing plastic products, the engineering plastics that can be needed are selected according to their environment. The selected plastic material, the finished product size accuracy, the weight of the parts, the quality requirements and the expected mold structure to choose the appropriate injection molding machine.
Among the relevant factors affecting precision injection molding, the mold is the key to obtain precision plastic products that meet the quality requirements. Mold design, mold design is reasonable will directly affect the quality of plastic products.
Since the size of the mold cavity is obtained by the required size of the plastic product plus the shrinkage rate of the material used, and the shrinkage rate is often a range of values recommended by the plastic manufacturer or engineering plastic manual, it is not only related to the gate form of the mold, the gate position and distribution, moreover, it is related to the crystal orientation (anisotropy) of the engineering plastic, the shape and size of the plastic product, the distance and position to the gate.
The main factors affecting the shrinkage of plastics include thermal 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 molded products.
Therefore, the mold designer must have rich experience in design and injection molding, must consider the relationship between these factors and injection conditions and its 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 gate cross-sectional area, product wall thickness, the content of reinforcing fillers in plastic materials, the crystallinity and orientation of plastic materials and other factors.
The influence of the above factors is also different depending on the plastic material, 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 the plastic from the solid (powder or pellets) to the liquid (melt) to the solid (product) transformation process. From the pellet to the melt, and then from the melt to the product, the middle must pass through the temperature field, flow field and density field. Under the combined action of these fields, different plastics (thermosetting or thermoplastic, crystalline or non-crystalline, reinforced or non-reinforced, etc.) have different polymer structure morphology and rheological properties.
All the factors that affect the above "field" will affect the physical and mechanical properties, size, shape, accuracy and appearance quality of plastic products.
In this way, the intrinsic relationship between process factors and polymer properties, structural morphology and plastic products will be expressed 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 and ordinary injection molding in the injection pressure and injection rate are also different, precision injection molding often use high pressure or ultra-high pressure injection, high-speed injection to obtain a smaller molding shrinkage.