Excessive burr generally occurs on the split surface, that is, between the movable mold and the static mold, the sliding portion of the slider, the gap of the insert, the pore of the ejector rod, etc., and the excess melt is formed on the
injection molded product . The burr, such a flash burr, can be leveraged during molding, which will further increase the burr of the flash, thereby causing partial depression of the mold, and the burr of the flash is formed into an enlarged vicious circle. Therefore, if you first find a flash burr, you must trim the mold as soon as possible. The main reason for the burr is too large:
1. Insufficient clamping force
Compared with the projected area of the molded part, if the clamping force is small, a gap will occur between the moving and static modes due to the action of the injection pressure, so that flash burrs are bound to occur. In particular, when the side gate is placed on the hole near the center of the workpiece, the burr is highly prone to occur because the molded gate requires a large injection pressure. Reducing the injection pressure or increasing the clamping force can eliminate this kind of defect. If the plasticity is changed to low pressure molding according to the specific situation, it is sometimes very effective.
2. The mold is not tightly matched
Firstly, the problem of the static clamping of the static and static molds is discussed. Although the mold itself is tightly clamped, when the injection molding machine with the toggle-type clamping mechanism is used, it is often caused by poor parallelism of the mold or poor adjustment of the clamping device. Such as the left and right sides of the mode is not. The phenomenon of equilibrium, that is, only the left and right sides are locked, and the other side is not closely attached. At this time, the tie rods (two or four pull tabs) must be adjusted to balance the secondary exhibition, and secondly, the mold itself is matched. Poor contact causes laxity. In particular, when there is a molded hole in the center of the workpiece, due to the supporting action of this portion, burrs are likely to occur when the clamping force is insufficient.
In addition, it is a sliding core. Since the trailing core is an action mechanism, burrs are often generated, so the cooperation of the sliding core is important. Especially for the Haf mode of the left and right type, the projected area of the side is also affected by the molding pressure. If the design is not able to fully withstand this pressure, burrs often occur. Regarding the insert gap and the ejector hole, not only the phenomenon that the burr vicious cycle increases, but also the ejection resistance is increased.
3. Mold deflection caused
If the mold is insufficient, the deflection will occur due to the injection pressure. If there is a hole near the center, the periphery of the hole will produce burrs. When the center hole is opened, the hole and the runner will also be generated. glitch. The burrs generated by this reason are caused by poor mold making, so it is difficult to repair. By using a reinforcing mold, the burr can be reduced.
4. Plastic fluidity is too good
It is simply because the plastic fluidity is too good, and in theory it is not the cause of burrs. However, when the plastic fluidity is too good, even a fine gap plastic can be drilled, so it is easy to burr. To eliminate such burrs, the melt temperature or injection pressure can be lowered, and the mold temperature or injection speed can be lowered.
5. Injecting too much melt
This is not the direct cause of glitch. In order to prevent shrinkage of the hole, it is wrong to inject too much melt, and it should be formed by increasing the injection time or holding time (refer to the shrinkage hole).
6. Foreign matter on the surface of the mold
There is a foreign object on the mold clamping surface, which will inevitably produce burrs. To solve this problem, it is obvious that it should be cleaned on the surface of the net mold so that the mold surface can be closely attached.
