Why will the injection molding process product burr and how to solve it?

Most of the burrs on the injection molding products occur on the parting surface, i.e., between the moving mold and the static mold, the sliding part of the slider, the gap of the insert, the hole of the top bar, etc., and the molten material flows into the parts, forming excess flying burrs on the parts.

First, what is the injection molding burr?

There are many names for burrs, such as flying edge, overflow edge, overflow material, etc. Different masters have different names, but they all mean the same thing.

Second, the cause of burrs

The occurrence of burrs in the injection molding process is due to the overflow of molten injection resin from the mold parting surface, especially if the burr firmly adheres to the mold parting surface, it will directly damage the mold parting surface, once the mold is damaged, and then the injection molding process, it will produce the phenomenon of burrs, and will also lead to a significant reduction in the life of the mold, burrs are generated by the following Causes.

1. insufficient clamping force

If the clamping force is small compared to the projected area of the molded part, the injection pressure will cause a gap between the moving and static mold, which will inevitably result in a flying burr. Especially when the side gate is placed on the hole near the center of the part, the burr is very likely to occur because of the high injection pressure required for this molding gate.


2. The mold local fit is not tight

The mold itself is tightly molded, but when the injection molding machine adopts the elbow rod type mold clamping mechanism, often due to the poor parallelism of the mold or poor adjustment of the mold clamping device, the phenomenon of unbalanced mold clampings such as the left and right sides, that is, the left and right sides only - side is locked, the other side is not close, at this time must adjust the tie bar (two or four cuttings) to make it balanced.
Secondly, there is also the mold itself because of the poor research and matching caused by the tight paste is not strict. Especially when there is a molding hole in the center of the part, due to the supporting role of this part, when the clamping force is not sufficient, it is also easy to appear burrs.

The other is the sliding core because along the moving core is the action mechanism, which often produces burrs, so the sliding core is very important. Especially for the left and right parting haters, the side projection area is also subject to molding pressure, and if the design is not fully able to withstand this pressure, burrs often occur. With regard to the gap between the insert and the hole of the ejector, it will not only produce the phenomenon of increasing burr vicious circle, but also increase the ejector resistance.

3. caused by mold flexing

If the original degree of the mold is not enough, the injection pressure will produce deflection, then if there is a hole near the center, burrs will be generated around the hole; also when the center hole is used to open the side gate, burrs will be generated around the hole and the sprue. Burrs from this cause are caused by poorly made molds, so they are more difficult to repair. The burr can be reduced by reinforcing the mold.

4. Plastic flowability is too good

Theoretically, it is not a cause of burr if the plastic flow is too good alone. However, when the plastic flow is too good, the plastic can get into even the smallest gap, so it is very easy to have burrs. To eliminate this burr, you can reduce the melt temperature or injection pressure, or reduce the mold temperature or injection speed.

5. Over-injection of melt material

This is also not a direct cause of burrs. It is wrong to inject too much melt in order to prevent shrinkage and should be taken to increase the injection time or holding time to mold (refer to shrinkage).

6. Foreign matter on the mold surface

Foreign matter on the mold surface is bound to produce burrs. To solve this problem, it is obvious that the surface of the mold should be cleaned to make the mold surface close.

Third, the burr solution

If the burr phenomenon is found to occur, the master of the injection molding process should stop the damage in time, find the cause early and give solutions

1、Do not use too high injection pressure in the injection process

2、Improve the clamping force

3、Adjust the injection volume and lower the temperature

MINDWELL specializes in Plastic Molding Services, our engineers are able to solve the problems of injection molded parts. The phenomenon of burr will directly lead to quality problems of injection molded products, which can be repaired in light cases, or directly lead to the scrapping of products in heavy cases. If a flying burr is found at the beginning, the mold must be repaired as soon as possible.