The plastic parts of the car are mostly injection molding
Plastic parts of the car are mostly injection molding
Plastic parts of the car are mostly injection molding, because these plastic parts themselves have high design accuracy, so that these plastic parts can not be used conventional injection molding. And must use precision injection molding process technology. In order to ensure the performance, quality and reliability of car precision plastic parts, injection molding out of high quality, in line with product design requirements of plastic products, plastic materials, injection molding equipment and mold and injection molding process must be continuously improved.
The main factors affecting precision injection molding The basis for determining precision injection molding is the precision of the injection molding product, that is, the dimensional tolerance of the product, the shape and position tolerance and the surface roughness. To carry out precision injection molding must have many related conditions, and the most essential is the plastic material, injection mold, injection molding process and injection molding equipment these four basic factors. When designing plastic products, engineering plastic materials should be selected first, and engineering plastics that can be precision injection molding must be selected those materials with high mechanical properties, dimensional stability, good creep resistance and environmental stress cracking resistance. Secondly, the suitable injection molding machine should be selected according to the selected plastic material, the dimensional accuracy of the finished product, the weight of the piece, the quality requirements and the expected mold structure. In the process of processing, the factors affecting precision injection molding products mainly come from the accuracy of the mold, injection shrinkage, and the environmental temperature and humidity of the product. In precision injection molding, the mold is one of the keys to obtain precision plastic products that meet the quality requirements. The mold used for precision injection molding should effectively 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 products will be inconsistent due to the difference in shrinkage. Therefore, it is very important to effectively control the shrinkage of plastic products in precision injection molding technology. Mold design is reasonable or not will directly affect the shrinkage rate of plastic products, because the mold cavity size is obtained by the size of plastic products plus the estimated shrinkage rate, and the shrinkage rate is recommended by the plastic manufacturer or engineering plastics manual within a range of values, it is not only related to the mold gate form, gate location and distribution, And the crystallization orientation of engineering plastics. The shape, size, distance to the gate and location of the plastic products. The main factors affecting the shrinkage rate of plastics are thermal shrinkage, phase change shrinkage, orientation shrinkage, compression shrinkage and elastic recovery, and these influencing factors are related to the molding conditions or operating conditions of precision injection products. Therefore, in the design of the mold must consider the relationship between these factors and injection molding 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 gate cross-sectional area, product wall thickness, the content of reinforced filler in the plastic material, the crystallinity and orientation of the plastic material and other factors. The influence of the above factors is also different due to different plastic materials, other molding conditions such as temperature, humidity, continued crystallization, internal stress after molding, and changes in the injection molding machine. Because the injection molding process is the plastic from solid powder or particle to liquid melt and solid product transformation process. From the particle to the melt, and then from the melt to the product, the middle must go through the temperature field, stress field, flow field and density field, etc., under the joint action of these fields, different plastics thermosetting or thermoplasticity, crystalline or amorphous, enhanced or non-enhanced, etc., have different polymer structure and rheological properties. All the factors that affect the above field will certainly affect the physical and mechanical properties, size, shape, precision and appearance quality of plastic products. In this way, the internal connection between the process factors and the properties of the polymer, the structural form and the plastic products will be expressed through the plastic products. The analysis of these internal connections is of great significance for reasonably drawing up injection molding process, reasonably designing and manufacturing molds according to drawings, and even reasonably selecting injection molding processing equipment. Precision injection molding and ordinary injection molding in the injection pressure and injection rate are also different, precision injection often uses high pressure or ultra-high pressure injection, high-speed injection to obtain a small molding shrinkage. In summary of the above reasons, in addition to considering the design elements of the general mold, the following points must be considered when designing the precision injection mold: б┘ the use of appropriate mold size tolerances; б┌ prevent forming shrinkage error; б█ prevent injection molding deformation; б▄ prevent demoulding deformation; The mold manufacturing error to a minimum; бя prevent mold precision error; 7 Maintain mold accuracy. to prevent forming shrinkage error. Because the shrinkage rate will change due to the injection pressure, therefore, for the single cavity mold, the cavity pressure in the cavity should be as consistent as possible; As for the multi-cavity mold, the cavity pressure between the cavity should be very small. In the case of single cavity multi-gate or multi-cavity multi-gate, it must be injected with the same injection pressure to make the cavity pressure consistent. For this, it must be ensured that the sprue position is balanced. In order to keep the pressure of the mold cavity in the mold cavity consistent, it is best to keep the pressure at the gate entrance consistent. The balance of pressure at the gate is related to the flow resistance in the runner. Therefore, before the gate pressure reaches the equilibrium, the flow should be balanced first. Because melt temperature and mold temperature affect the actual shrinkage rate, so in the design of precision injection mold cavity, in order to facilitate the determination of molding conditions, we must pay attention to the arrangement of cavity.