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What do you know about the prevention methods of poor injection size?

Update:24-11-2020
Summary:

Prevention of poor injection size Reasons for the small […]

Prevention of poor injection size

Reasons for the small size of injection molded parts:
1. Most materials have the characteristics of thermal expansion and contraction. The same is true for resins. Therefore, the molded product begins to shrink after being molded and is cooled to the same temperature as normal. However, the problem is that if the final shrinkage is too large, The size of the molded product becomes too small, resulting in a small size defect;
One of the reasons for this is that when determining the initial mold size, the basic shrinkage rate of various resins is considered and the numerical value is calculated as a reference. However, even if the shrinkage rate is considered, the molded product that shrinks in the actual process The size is smaller than the specification size. Therefore, it is necessary to re-correct the mold in the above situation.

Secondly, it is related to the environment when it is formed. Among these are the dry state of the material, the mixing rate of the reused material, and the forming conditions. The most important thing is the forming conditions, because the mold temperature and injection pressure can make The amount of shrinkage increases, so it is necessary to pay attention; in general, if the injection pressure is increased, the size of the molded product will become larger, and if the temperature of the mold is increased, the size will tend to become smaller. These are simple and understandable terms. : The size of the molded product is directly proportional to the injection pressure and injection time; it is inversely proportional to the mold temperature.
3. In the phenomenon that often occurs in long-term mass production, the exhaust gas generated from the material during injection accumulates in the mold, so the filling of the material becomes poor and the size is small. Regarding the content related to exhaust gas, The key problem is that it is impossible to have no defects in the precision plastics of injection molding. Because the defects are a more important issue, we will consider it in detail in the future.
Countermeasures during forming:
1. Increase injection pressure
2. Reduce mold temperature
3. Extend injection and cooling time
4. Confirm whether the type of forming machine and mold are suitable.
5. Mold countermeasures
6. In the case of new molds, the bad parts of reprocessing
In mass production, this kind of situation occurs due to the wear of the mold or the obstruction of the exhaust gas. First, all the molds are cleaned to remove the exhaust gas and then the molding is performed again, and it must be confirmed.
Reasons for poor size:
The phenomenon that is completely opposite to the small size defect is called the large size defect. Therefore, the content of the cause of the defect is the same as that of the small size. First, the size on the mold is not made correctly, the second is the problem of the molding environment, and the third is that the surface of the mold is acidified and corroded because of exhaust gas. Circumstances caused by the time.
Countermeasures for large size:
1. Reduce injection pressure
2. Increase mold temperature
3. Reduce injection and cooling time
4. Confirm whether the type of forming machine is suitable for the mold
5. Mold countermeasures
6. Re-correct the part that causes the size to be too large

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