1. Causes of dents 1.1 The thickness of each part of the product is different 1.2 Insufficient pressure inside the mold 1.3 Insufficient mold cooling 1.4 Deformation due to the insufficient cooling time

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How To Remove Mold Dents?
1. Causes of dents
1.1 The thickness of each part of the product is different
1.2 Insufficient pressure inside the mold
1.3 Insufficient mold cooling
1.4 Deformation due to the insufficient cooling time
2. Related knowledge
2.1 In the process of producing products, dents are the most frequent occurrence of undesirable
phenomena. The plastic injected into the mold shrinks in volume when it is cooled. The early
cooling part, that is, the surface hardens first, and bubbles will be generated inside. The so-called
dent is slow cooling. The part of the bubble produces a conspicuous concave surface in the
direction of the bubble shrinkage.
2.2 Materials with large shrinkage are also prone to dents. When changing the molding
conditions to eliminate dents, the setting conditions should be set in the direction of small
shrinkage.
That is, the mold temperature and barrel temperature decrease, and the injection pressure
increases, but it should be noted that this may cause residual internal stress.
2.3 Because the dents are better to be inconspicuous, if they do not affect the appearance, they
are deliberately processed into a corroded pattern on the mold, such as grains and grains.
If the molding material is HIPS, reducing the mold temperature to reduce the finish is also
effective. However, once dents occur in these methods, it is difficult to repair polished products.

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3. The solution
3.1 Instant
Increase injection pressure, extend injection holding time, reduce barrel temperature and mold
temperature, and force cooling where dents are generated.
3.2 Short-term
Fill up the flow edge where the dent is generated. When the material in the dented area has a
narrow place, make this part thick.
3.3 Long-term
The difference in the thickness of the designed product should be completely avoided.
Reinforcing ribs that are prone to dents, the long and narrow shape should be as short as
possible
4. Differences in materials
Materials with large molding shrinkage have large dents. For example, PE, PP, even if only a slight
reinforcement rib, will produce dents.
5. References
5.1 When the temperature is reduced to no dents, if the material in the cavity is still under
pressure, it should be considered that no dents will be generated.
The pressure in the mold of the material surrounding the mold is the static pressure, which is not
always the same everywhere.
The pressure of the part close to the gate is high. If the material has a wide through edge,
because of the transmission of pressure to the corners, the pressure difference between the part
near the gate and the place far away from the gate is very small compared with the overall
pressure, and no depression will occur. It is also possible to obtain products without residual
internal stress.
When part of the material flows into a difficult place, this place has high pressure, and the
pressure in other places decreases, and dents are generated. This part of the residual high
pressure is the internal stress of the product.
In an ideal state, the material temperature rises with the mold temperature, the fluidity of the
material is better, and the injection becomes bottom in the static pressure state.
5.2 When changing the molding conditions, the combination of temperature, pressure, and time
should be prepared in advance, and the results can be known early by proceeding in sequence.
First of all, after the time has become long, it is easy to know every small change in pressure. It
should be noted that the results when the temperature changes are obtained after the injection
of the material, and the results when the temperature drops before production.