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Injection Mold Failure and Its Elimination

During the working process of injection molds, there will always be more or less failures, which will have adverse effects on product quality, productivity, molds, etc., which will be described below.


Ⅰ. Injection mold deformation and its elimination method


Mold deformation refers to the excessive elastic deformation or plastic deformation of the mold during the working process, which makes the mold not work normally or the quality of the product is unqualified. The reasons and troubleshooting methods are as follows.


1. Insufficient rigidity


In injection molding, the mold is subject to huge holding pressure. If this pressure causes permanent deformation of the mold, the mold will not be usable, but even within the elastic limit, the deformation of the mold can be restored, and when deformed The solidified molding will make it difficult to open the mold, or even impossible to open. When this happens, it is impossible to structurally modify the mold, but the injection pressure can be appropriately reduced, or a frame can be added from the outside to enhance the rigidity. Although it is not good-looking, it is also applicable.


2. Mold assembly disorder


If the mold is improperly assembled, such as poor centering of the mold, the clamping part of the mold and its joints are not accurately centered, which will make the melt filling unbalanced and easily cause deformation or misalignment of the injection mold tool. In this regard, the mold should be reassembled, and the unbalanced filling can sometimes be corrected by correcting the gate.


Ⅱ. The solution to the damage of the injection mold cavity


Cavity is where injection molding products form plastic parts. Its damage will directly affect product quality. Cavity damage is the hard damage on the inner surface of the cavity, which causes scratches, pits, cracks and other defects on the surface. These damages The causes and their elimination methods are as follows.


1. Hard objects damage the cavity


Sometimes it is difficult to take out the plastic parts after the mold is opened, so hard tools such as screwdrivers are used to take them out, which is easy to damage the cavity. In addition, after the mold is opened, hard objects such as wrenches and hammers are accidentally dropped into the cavity, resulting in damage to the cavity.


2. Improper operation


If the mold is closed before the plastic part is taken out, especially during automatic molding, the cured plastic part is easy to damage the cavity and the mold.


3. Damage repair


After the cavity is damaged, it is difficult to continue to work without repair. There are several ways to repair the cavity.


(1) Welding. Welding is a commonly used repair method, the most commonly used welding method is gas welding. If electric welding is used, due to the high temperature, the mold is prone to deformation or even cracking. If electric welding is used to repair, the mold must be preheated and heat treated after welding.


(2) Inserts. For small and deep damage, inserts can be added to repair, usually drill holes and insert inserts, when drilling, be careful not to drill through the cooling water channel and screw holes. The fit between the insert and the cavity should be tight, and it should be smoothed after installation.


(3) Electroplating. For defects with a depth of less than 0.5mm, it is better to repair them by electroplating, which can be copper-plated or chrome-plated.


(4) Knock. For the cavity with softer materials, it is possible to drill a blind hole on the back of the damaged part, and then tap the bottom of the blind hole to make the damaged part protrude; or tap at a distance 3mm away from the damaged part to make the concave part protrude. Then grind, and polish the raised part.


Ⅲ. Injection mold rust and its elimination


Injection molding supplies are mostly made of tool steel, which will encounter corrosive gases, water and other substances that cause rust during work. Plastic parts made from rusty molds will cause quality problems and therefore need to be excluded.


1. Gas generated by melt decomposition


Some raw materials will produce volatile gas after heating, and many raw materials will also produce volatile gas when overheated. These gases are mostly corrosive, and they permeate around the machine. When the mold is not working, they will corrode the mold. In this regard, when the machine stops working, wipe the mold with a soft cloth and close the mold. If it is not used for a long time, the mold cavity should be sprayed with anti-rust agent, and butter should be also applied when closing the mold, and the gate is blocked.


2. Cooling water in the mold


The mold is cooled by multi-pass cooling water, so there is more water vapor around the machine. If the mold is cooled below the dew point, the moisture in the air will form water droplets on the surface of the mold, and it will easily rust if it is not wiped off in time. Especially after the mold stops working, condensation water will be generated very quickly. Therefore, don't stop molding easily, even if you want to stop, turn off the cooling water and dry the mold.


3. Carbide produced during molding


After the mold works for a long time, carbides are precipitated and decomposed in the molding material, which often makes the mold wear, corrode or rust. In this regard, if carbide is found, it should be wiped off and cleaned with a dry cloth immediately.


In order to reduce the production cost of the injection moulding process for the entire enterprise, it is necessary to work hard on both the quality of the injection mold and the later maintenance to improve the service life of the entire injection mold, thereby reducing product costs and enhancing the overall market competitiveness.

Keyplast Injection Molding

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