2019年12月10日星期二

What is a precision injection molding


What is a precision injection molding

Precision injection molding generally refers to a process that requires high accuracy and surface quality of molded products. Some people also believe that precision injection molding refers to an injection molding process that has a dimensional accuracy of 0.01 to 0.001 mm. With the rapid development of medical, communications, automotive and other industries, people's requirements for the accuracy and height of plastic products are increasing day by day. Traditional plastic molding processes have been difficult to meet the current high standards. At the same time, injection molding is one of the most important plastic molding methods. First, as a result, precision injection molding technology is receiving more and more attention from people. Therefore, precision injection molding technology continues to advance, and new technologies continue to emerge.
Precision injection molding requires that the product not only has high dimensional accuracy, minimal warping deformation, excellent transfer characteristics, but also excellent optical performance, etc., so it has an excellent performance on injection molding machines, injection molds, molding processes, and raw materials. And formula are always special requirements, many factors affect precision injection molding.

What are the factors that affect precision injection molding?

Generally, PS, ABS, AS, PMMA, PC, PPO, PSU can be used to form products with level 3 and 4 accuracies; PA series can be used to form products with level 4 accuracy; and POM, PP, PE, TPE, etc. are not suitable for forming level 4 or higher Precision products.
In addition, due to the low shrinkage and high dimensional stability of inorganic-filled or glass-reinforced plastics, they are often used to form precision products. Process characteristics of precision injection molding are mainly high injection pressure, fast injection speed, and precise temperature control.

(1) High injection pressure the test proves that for different plastic varieties, shapes, and sizes, the pressure required for precision injection molding should be 180-250MPa (the injection pressure used for ordinary injection molding is generally 40-200MPa), in some special cases, the requirements are higher. The highest has reached about 450MPa.

(2) Fast injection speed The size of the injection speed obviously affects the size of the product, and more importantly, it can reduce the dimensional tolerance of the product. In order to improve the accuracy of injection molded parts, especially for the molding of products with complex shapes, variable-speed injection must be developed, that is, the injection speed is changed, and the change rule is determined by the structural shape of the part and the properties of the plastic.

(3) Temperature control must be precise. The temperature has a great influence on the molding quality of the product and is one of the three major process conditions for injection molding. For precision injection molding, there are both temperature problems and temperature control accuracy issues. In the process of precision injection molding, if the temperature is not accurately controlled, the fluidity of the plastic melt and the molding performance and shrinkage of the product will not be stable, so the accuracy of the product cannot be guaranteed.

From this perspective, when precision injection molding is used, the temperature range must be strictly controlled for both the barrel and the nozzle and the injection mold.
For example, during precision injection molding, PID controllers are used for the temperature at the barrel and nozzle, and the temperature range is controlled within 1 ° C. For ordinary injection molding machines, the temperature can reach 20 ° C to 300 ° C. In order to ensure the accuracy of the product during injection molding production, in addition to strictly controlling the temperature of the barrel, nozzle and mold, attention must also be paid to the impact of the ambient temperature on the accuracy of the product after demolding.


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