Location： Home > Discussion on the causes and solutions of excessive burrs in injection molded products
Uploaded：2023-11-22Click：0
Product burrs (flying edges) are a common injection molding problem and are also very prone to injection molding problems.
The most important part of the excessive flash is still the processing of the parting surface, that is, between the dynamic and static molds, the sliding parts of the slider, the fitting gap of the insert, the top rod hole gap, and other places where the molten material flows into, forming excess flash burrs on the fingertips.
Flash like this plays a crucial role in forming. If left untreated, it can further increase the burrs on the flash, resulting in dents in the corresponding parts of the mold parting surface, leading to a vicious cycle of further increase in brush size. Therefore, if any burrs are found during regular inspections, we should repair the mold as soon as possible.
The main and most common reasons for burrs are as follows:
1. The partial fitting of the mold parting surface is not tight
Whether the research and matching of the parting surface is tight can directly lead to the existence of flash edges in the product; This depends on the skill of the mold fitter. Mold research and assembly is a delicate task that tests the patience and skills of mold fitters. This is also one of the most direct reasons for the product to take off, so when we find that the mold is not properly matched, the solution is to re install the mold fitting machine for matching.
2. The locking structure of the injection molding machine caused
If our mold itself is very precise in research and development, but when using an injection machine with an elbow bar locking mechanism for molding, there is often a phenomenon of uneven locking on the left and right sides due to poor parallelism of the mold or poor adjustment of the locking device. That is, only one side of the left and right sides is locked tightly, and the other side is not tightly attached. At this time, it is necessary to adjust the pull rod (two or four pull rods) to make it evenly spread.
3. Insufficient locking force
Compared to the projected area of formed parts, if the clamping force is small, gaps will appear between the dynamic and static molds due to the injection pressure, which will inevitably lead to flash and burrs. Especially when placing the side gate on the hole near the center of the workpiece, it is prone to burrs due to the high injection pressure required for this type of forming gate.
Generally, experienced mold factories rarely experience flash due to insufficient locking force, as from the beginning of design, our molds should be matched with the customer's machine to meet the locking force. To solve such problems, we can either reduce the injection pressure or replace the machine, choose injection equipment with higher locking force for production, or use plastic with good fluidity for low-pressure molding according to specific circumstances.
4. Mold warping caused
If the rigidity of the mold is insufficient, it will deflect under the injection pressure. At this time, if there is a hole near the center, burrs will appear around the hole; When using the center hole to open a side gate, burrs will also appear around the hole and gate. The burrs generated by this reason are caused by poor mold manufacturing, so it is difficult to repair.
5. Excessive injection of molten material
In general, it does not happen. Usually, when adjusting machine parameters, due to local material shortage or excessive injection of molten material to prevent shrinkage, the mold will be expanded, resulting in flash generation. This approach is incorrect and should be taken by increasing injection time or holding time for molding.
6. There are foreign objects on the surface of the mold
There are foreign objects on the clamping surface of the mold, which will inevitably produce burrs. So, we need to inspect the surface of the mold before starting production. In addition, after the mold is produced, we should also pay attention to timely cleaning and daily maintenance. This not only reduces the occurrence of mold problems, but also extends the service life of the mold.
The most important part of the excessive flash is still the processing of the parting surface, that is, between the dynamic and static molds, the sliding parts of the slider, the fitting gap of the insert, the top rod hole gap, and other places where the molten material flows into, forming excess flash burrs on the fingertips.
Flash like this plays a crucial role in forming. If left untreated, it can further increase the burrs on the flash, resulting in dents in the corresponding parts of the mold parting surface, leading to a vicious cycle of further increase in brush size. Therefore, if any burrs are found during regular inspections, we should repair the mold as soon as possible.
The main and most common reasons for burrs are as follows:
1. The partial fitting of the mold parting surface is not tight
Whether the research and matching of the parting surface is tight can directly lead to the existence of flash edges in the product; This depends on the skill of the mold fitter. Mold research and assembly is a delicate task that tests the patience and skills of mold fitters. This is also one of the most direct reasons for the product to take off, so when we find that the mold is not properly matched, the solution is to re install the mold fitting machine for matching.
2. The locking structure of the injection molding machine caused
If our mold itself is very precise in research and development, but when using an injection machine with an elbow bar locking mechanism for molding, there is often a phenomenon of uneven locking on the left and right sides due to poor parallelism of the mold or poor adjustment of the locking device. That is, only one side of the left and right sides is locked tightly, and the other side is not tightly attached. At this time, it is necessary to adjust the pull rod (two or four pull rods) to make it evenly spread.
3. Insufficient locking force
Compared to the projected area of formed parts, if the clamping force is small, gaps will appear between the dynamic and static molds due to the injection pressure, which will inevitably lead to flash and burrs. Especially when placing the side gate on the hole near the center of the workpiece, it is prone to burrs due to the high injection pressure required for this type of forming gate.
Generally, experienced mold factories rarely experience flash due to insufficient locking force, as from the beginning of design, our molds should be matched with the customer's machine to meet the locking force. To solve such problems, we can either reduce the injection pressure or replace the machine, choose injection equipment with higher locking force for production, or use plastic with good fluidity for low-pressure molding according to specific circumstances.
4. Mold warping caused
If the rigidity of the mold is insufficient, it will deflect under the injection pressure. At this time, if there is a hole near the center, burrs will appear around the hole; When using the center hole to open a side gate, burrs will also appear around the hole and gate. The burrs generated by this reason are caused by poor mold manufacturing, so it is difficult to repair.
5. Excessive injection of molten material
In general, it does not happen. Usually, when adjusting machine parameters, due to local material shortage or excessive injection of molten material to prevent shrinkage, the mold will be expanded, resulting in flash generation. This approach is incorrect and should be taken by increasing injection time or holding time for molding.
6. There are foreign objects on the surface of the mold
There are foreign objects on the clamping surface of the mold, which will inevitably produce burrs. So, we need to inspect the surface of the mold before starting production. In addition, after the mold is produced, we should also pay attention to timely cleaning and daily maintenance. This not only reduces the occurrence of mold problems, but also extends the service life of the mold.