Most of the burrs occur on the splitting surface, that is, between the dynamic and static models, slider sliding parts, insert gaps, ejector rod holes and other places into the melt, forming excessive flash burrs on the parts.
Such burrs play a leverage role in the forming process, which will further increase the burrs on the flying edge, resulting in a local depression of the die, and the burrs on the flying edge will enter a vicious circle of increase when they are formed. Therefore, if the flash burr is found at the beginning, the die must be repaired as soon as possible.
There are several reasons for burrs
1. lack of clamping force.
Compared with the projection area of the moulded parts, if the clamping force is smaller, there will be a gap between the dynamic and static moulds due to the injection pressure, which will inevitably lead to a flash burr. Especially when the side gate is placed on the hole near the center of the workpiece, because this kind of moulding gate needs a large injection pressure, it is easy to appear burrs.
This defect can be eliminated by reducing injection pressure or increasing clamping force. It is sometimes effective to use plastic with good fluidity to form under low pressure according to specific conditions.
2. Insufficient local matching of dies
Firstly, the problem of inadequate clamping of dynamic and static die is discussed. Although the clamping of the die itself is tight, when the injection machine with elbow bar type clamping mechanism is used, the phenomenon of imbalance between the left and right sides of the clamping die is often caused by the poor parallelism of the die or the bad adjustment of the clamping device, that is, only one side of the left and right side is locked, and the other side is locked. When the edges are not close to each other, it is necessary to adjust the pull rods (two or four pull cuttings) so as to make them develop evenly.
Secondly, there is also a lack of tightness due to poor research and matching of the die itself. Especially when there are forming holes in the center of the part, because of the supporting role of this part, burrs are easy to appear when the clamping force is insufficient.
In addition, the sliding core, because the moving core is an action mechanism, it often produces burrs, so the matching of sliding core is very important. Especially for the left and right parting of the Huff die, its side projection area is also affected by the forming pressure. If the design can not fully withstand this pressure, burrs will often appear. With regard to insert gap and ejector rod hole, not only will the phenomenon of burr vicious circle increase, but also will increase ejection resistance.
3. Mould deflection
If the original degree of the die is insufficient, it will be deflected by the injection pressure. At this time, if there are holes near the center, there will be burrs around the hole; and when the center hole is used to open the side gate, burrs will also occur around the hole and the gate. The burr caused by this reason is caused by poor die making, so it is difficult to repair. The burr can be reduced by reinforcing the die.
4. Excessive fluidity of plastics
Simply because the plastic fluidity is too good, in theory, it is not the cause of burrs. However, when the plastic fluidity is too good, even tiny slits of plastic can be drilled into, so it is very easy to appear burrs. To eliminate this burr, the melt temperature or injection pressure can be reduced, and the temperature of the mould or injection speed can also be reduced.
5. Too much melt is injected
This is not the direct cause of burrs. It is wrong to inject too much melt in order to prevent shrinkage. The injection time or holding time should be increased to form (refer to shrinkage).
6. Foreign body on die surface
There are foreign bodies on the clamping surface of the die, which will inevitably produce burrs. To solve this problem, it is obvious that the surface of the net die should be cleaned so that the closing surface can be closely adhered to.
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