What are the reasons for excessive burrs in injection molded products


The burrs mostly occur on the parting surface, that is, […]

The burrs mostly occur on the parting surface, that is, between the movable mold and the static mold, the sliding part of the slider, the gap of the insert, the hole of the ejector, etc., the melt flows into the molten material, and the excess flash burr is formed on the part. , Such flash burrs, when forming a leverage, will further increase the flash burrs, resulting in partial depression of the mold, and the flash burrs will enter a vicious circle of increase when formed. Therefore, if flash burrs are found at the beginning, the mold must be trimmed as soon as possible.

There are several reasons for the occurrence of burrs
1. Insufficient clamping force
Compared with the projected area of ​​the molded part, if the clamping force is small, there will be a gap between the moving and static molds due to the injection pressure, which will inevitably cause flash burrs. Especially when the side gate is placed on the hole near the center of the part, because this kind of molding gate requires a large injection pressure, it is very easy to appear burrs. Reducing the injection pressure or increasing the clamping force can eliminate this defect. If you switch to low-pressure molding with good fluidity according to the specific situation, it is sometimes very effective.
2. Partial mold fit is not tight
First of all, discuss the problem of loose clamping of the dynamic and static molds. Although the mold itself is tightly closed, when the injection machine with a toggle-type clamping mechanism is used for molding, it is often caused by poor mold parallelism or poor adjustment of the clamping device. For example, the left and right sides of the mold are not locked. The phenomenon of equilibrium, that is, only one side is locked on the left and right sides, and the other side is not tightly attached. At this time, the tie rods (two or four tie rods) must be adjusted to make them balanced. Secondly, it is also due to the development of the mold itself. Poor adhesion results in lax adhesion. Especially when there is a molding hole in the center of the part, due to the supporting effect of this part, burrs are also easy to appear when the clamping force is insufficient.
In addition, it is a sliding core. Because the moving core is an action mechanism, burrs are often produced, so the cooperation of the sliding core is very important. Especially for the left and right parting of the Huff die, the projected area of ​​the side is also affected by the molding pressure. If the design cannot fully withstand this pressure, burrs will often appear. Regarding insert gaps and ejector pin pores, not only will the vicious circle of burrs increase, but also the ejection resistance will increase.

3. Caused by mold deflection
If the original degree of the mold is insufficient, it will be deflected by the injection pressure. At this time, if there is a hole near the center, burrs will be generated around the hole; and when the center hole is used to open the side gate, the hole and the periphery of the runner will also be generated. glitch. The burr caused by this reason is caused by poor mold making, so it is more difficult to repair. Reinforcing the mold can reduce the burr.
4. Plastic fluidity is too good
Simply because the plastic has too good fluidity, it is not theoretically the cause of the burr. However, when the fluidity of the plastic is too good, even the tiny gaps can be penetrated by the plastic, so burrs are prone to appear. To eliminate such burrs, you can reduce the melt temperature or injection pressure, and also reduce the mold temperature or injection speed.