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Injection mold failure and its elimination
by：Vowin Rapid Prototyping
2023-02-11
During the working process of injection molds, there will always be more or less failures, which will adversely affect product quality, productivity, molds, etc., which will be analyzed below.
(1) Mold deformation and its elimination
Mold deformation refers to the excessive elastic deformation or plastic deformation of the mold during the working process, so that the mold cannot work normally or the product quality is unqualified. The reasons and troubleshooting methods are as follows.
1. Insufficient rigidity
During injection molding, the mold should bear huge pressure protection pressure. If this pressure permanently deforms the mold, the mold will become unusable. But even within the elastic limit, the deformation produced by the mold can be recovered, and the solidification molding during deformation can make the mold difficult or even impossible to open. In this case, it is impossible to structurally modify the mold, but the injection pressure can be appropriately reduced, and the frame can also be added from the outside to enhance rigidity. It's not pretty, but it's usable.
2. Mold assembly misalignment
If the mold is improperly assembled, such as poor centering of the mold, the clamping part of the mold and its joints are not centered accurately, which will make the melt filling unbalanced and easily cause mold deformation or dislocation. In this regard, the mold should be reassembled to correct mold imbalances and sometimes gates.
(2) Cavity damage and its elimination
The cavity is the place where the plastic part is formed, and its damage will directly affect the product quality. Cavity damage is hard damage on the inner surface of the cavity, causing surface scratches, pits, cracks and other defects. The causes of these damages and their elimination methods are as follows.
1. Hard objects damage the cavity
Sometimes it is difficult to take out the plastic part after the mold is opened, so use a hard tool such as a screwdriver to take it out reluctantly, and it is easy to damage its cavity. In addition, after the mold is opened, the wrench is accidentally pulled. Hard objects such as a hammer fall into the second cavity, causing damage to the cavity.
2. Improper operation
If the plastic is not taken out, close the mold, especially during automatic molding, the cured plastic parts are easy to damage the cavity and mold.
3. Repair damage
After the cavity is damaged, it is difficult to continue working without repair. The cavity repair method is as follows.
(1) Welding. Welding is a common repair method, the most common method of welding is gas welding. If electric welding is used, the mold is easily deformed or even cracked due to the high temperature. It is repaired by electric welding, the mold is preheated, and heat treatment is performed after welding.
(2) Inserts. The area is small. .Deep damage can be repaired by adding inserts. Generally, the inserts are inserted after drilling. Be careful not to drill cooling water channels and screw holes when drilling. The fit between the insert and the cavity should be tight, and it should be smooth after installation.
(3) Electroplating. Defects with a depth of less than 0.5mm are best repaired by electroplating, which can be copper-plated or chrome-plated.
(4) Tap. For the cavity with soft material, you can drill a blind hole on the back of the damaged part, and then tap the bottom of the blind hole to make the damage protrude; or tap the outside 3mm away from the damage to make the concave part protrude, and then grind the protruding part Flat. Grinding. Polishing.
(3) Mold rust and its elimination
Injection molds are mainly made of tool steel, and encounter corrosive gases, water and other substances that cause rust during work. Plastic parts made from rusty molds present quality issues and need to be ruled out.
1. Gas produced by melt decomposition
Some raw materials will produce volatile gas after heating, and many raw materials will also produce volatile gas when they are overheated. Most of these gases are corrosive and spread around the machine. They corrode the mold when it is not working. 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, spray anti-rust agent in the mold cavity, and butter should be applied when closing the mold to block the gate.
2. Cooling water in the mold
There is more cooling water in the mold to wake up the cooling, so there is more water and air around the machine. If the mold is cooled to the dew point, the moisture in the air will form water droplets on the surface of the mold, and if it is not wiped in time, it will easily rust. Especially after the mold stops working, condensate will be produced soon. Therefore, don't stop molding easily, even if you stop, turn off the cooling water and dry the mold.
3. Carbide produced during the forming process
After the mold works for a long time, the carbide precipitates and decomposes 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 with a dry cloth immediately. Wipe it clean.
(1) Mold deformation and its elimination
Mold deformation refers to the excessive elastic deformation or plastic deformation of the mold during the working process, so that the mold cannot work normally or the product quality is unqualified. The reasons and troubleshooting methods are as follows.
1. Insufficient rigidity
During injection molding, the mold should bear huge pressure protection pressure. If this pressure permanently deforms the mold, the mold will become unusable. But even within the elastic limit, the deformation produced by the mold can be recovered, and the solidification molding during deformation can make the mold difficult or even impossible to open. In this case, it is impossible to structurally modify the mold, but the injection pressure can be appropriately reduced, and the frame can also be added from the outside to enhance rigidity. It's not pretty, but it's usable.
2. Mold assembly misalignment
If the mold is improperly assembled, such as poor centering of the mold, the clamping part of the mold and its joints are not centered accurately, which will make the melt filling unbalanced and easily cause mold deformation or dislocation. In this regard, the mold should be reassembled to correct mold imbalances and sometimes gates.
(2) Cavity damage and its elimination
The cavity is the place where the plastic part is formed, and its damage will directly affect the product quality. Cavity damage is hard damage on the inner surface of the cavity, causing surface scratches, pits, cracks and other defects. The causes of these damages and their elimination methods are as follows.
1. Hard objects damage the cavity
Sometimes it is difficult to take out the plastic part after the mold is opened, so use a hard tool such as a screwdriver to take it out reluctantly, and it is easy to damage its cavity. In addition, after the mold is opened, the wrench is accidentally pulled. Hard objects such as a hammer fall into the second cavity, causing damage to the cavity.
2. Improper operation
If the plastic is not taken out, close the mold, especially during automatic molding, the cured plastic parts are easy to damage the cavity and mold.
3. Repair damage
After the cavity is damaged, it is difficult to continue working without repair. The cavity repair method is as follows.
(1) Welding. Welding is a common repair method, the most common method of welding is gas welding. If electric welding is used, the mold is easily deformed or even cracked due to the high temperature. It is repaired by electric welding, the mold is preheated, and heat treatment is performed after welding.
(2) Inserts. The area is small. .Deep damage can be repaired by adding inserts. Generally, the inserts are inserted after drilling. Be careful not to drill cooling water channels and screw holes when drilling. The fit between the insert and the cavity should be tight, and it should be smooth after installation.
(3) Electroplating. Defects with a depth of less than 0.5mm are best repaired by electroplating, which can be copper-plated or chrome-plated.
(4) Tap. For the cavity with soft material, you can drill a blind hole on the back of the damaged part, and then tap the bottom of the blind hole to make the damage protrude; or tap the outside 3mm away from the damage to make the concave part protrude, and then grind the protruding part Flat. Grinding. Polishing.
(3) Mold rust and its elimination
Injection molds are mainly made of tool steel, and encounter corrosive gases, water and other substances that cause rust during work. Plastic parts made from rusty molds present quality issues and need to be ruled out.
1. Gas produced by melt decomposition
Some raw materials will produce volatile gas after heating, and many raw materials will also produce volatile gas when they are overheated. Most of these gases are corrosive and spread around the machine. They corrode the mold when it is not working. 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, spray anti-rust agent in the mold cavity, and butter should be applied when closing the mold to block the gate.
2. Cooling water in the mold
There is more cooling water in the mold to wake up the cooling, so there is more water and air around the machine. If the mold is cooled to the dew point, the moisture in the air will form water droplets on the surface of the mold, and if it is not wiped in time, it will easily rust. Especially after the mold stops working, condensate will be produced soon. Therefore, don't stop molding easily, even if you stop, turn off the cooling water and dry the mold.
3. Carbide produced during the forming process
After the mold works for a long time, the carbide precipitates and decomposes 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 with a dry cloth immediately. Wipe it clean.
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