PRODUCTION PROBLEMS AND SOLUTIONS(3)

There will be defects in the production of injection molded parts

In the production of injection molded parts, the defect of weak encapsulation occurs, which refers to the plastic parts that use secondary overmolding, and the soft plastic that is secondarily covered by plastic parts is easy to peel off, as shown in Figure 3-89. The process of secondary overmolding is to first use the first plastic to mold the inner part, then rotate the movable mold, and then use the second plastic to mold the outer part, so that the outer part is superimposed on the inner part, as common Mobile phone shells and other electronic products. For the power tool industry, the plastic parts are often divided into two sets of molds. The first set of molds is used to form the inner part, the second set of molds is used to encapsulate, and the second layer of plastic is generally TPE soft rubber. The common defects of this process are weak encapsulation, poor appearance, short shots, etc.
In the secondary overmolding process, the commonly used solutions for weak encapsulation are as follows:
1) Immediately encapsulate after injection molding, preferably two-color injection molding.
2) When overmolding, the overmolded part of the inner material should be clean (don’t clean it manually), free of oil and dust.
3) When the encapsulation is found to be weak, the outer soft rubber should be removed immediately, and no further encapsulation should be performed.
4) When injection molding, higher injection speed and higher melt temperature should be used, which is beneficial to improve the firmness of bonding.
5) After encapsulation, it should be placed for a period of time before testing the quality of the plastic parts to judge whether the encapsulation effect is up to standard.
6) The surface of the encapsulated part should avoid using release agent.
7) When there is a problem with plastic raw materials, it should be considered from two aspects of the inner and outer materials. You cannot only consider the material factors of the outer layer. The encapsulated material also has an impact on the encapsulation effect, especially the additives in the hard rubber. 

Control measures to prevent injection molding parts from fuel injection and poor electroplating in injection molding production

①Try not to use release agent. When you must use it, you can only use a dry release agent or a neutral release agent to lightly spray the movable mold (commonly known as “back mold”), but the injection molded parts that require electroplating must not be used. When spraying, pay attention that the oil stains can’t float to the fixed mold (commonly known as the “front mold”). If possible, it is best to apply the method to prevent the release agent from splashing to the position where the front chess needs to be sprayed. However, if it is applied too much, it may leave oil stains on the outer surface of the injection molded part during injection. You need to be more careful when spraying silver oil.

②Keep the mold clean. There are many oil stains on the molds that have just started production, and it is difficult to clean them after a long time. Therefore, they must be thoroughly cleaned with detergent (commonly known as “mold washing water”) before production. For the plastic parts that need to be sprayed with silver oil in the subsequent process, the cavity of the mold should be thoroughly cleaned regularly.

③The soft PVC plastic parts need to be soaked in water, and there should be no oil stains in the water. The water-filled basin cannot be placed under the injection molding machine to prevent the machine oil from dripping into the water. Because this is a less noticeable place, sometimes a large number of injection molded parts lose oil after spraying, but the cause cannot be found.