1. The cause of the dent
(1) The thickness of each part of the product is different.
(2) The internal pressure of the mold is insufficient.
(3) The mold cooling is insufficient.
(4) Deformation due to insufficient cooling time.
2. The solution
(1) Instant. Increase the injection pressure, extend the injection dwell time, reduce the barrel temperature and mold temperature, and force cooling in the place where the dent is generated.
(2) Short-term. Fill the flow edge where the dent is created. When there is a narrow place on the side of the material where the dent is generated, the side is thick.
(3) Long-term. The difference in thickness of the design article should be completely avoided. Ribs that are prone to dents should be as short as possible.
When the temperature is lowered to no dents, if there is pressure in the material in the cavity, it should be considered that no dents will occur. The pressure within the mold, ie, the static pressure, of the material surrounding the mold is not necessarily anywhere. The pressure near the gate is high. If the material is wide, because the pressure to the corners is transmitted, the pressure difference between the near gate and the gate is not much different from the pressure of the whole. It is also possible to obtain a product which does not leave internal stress.
When part of the material flows into a difficult place, there is a high pressure in this place, and the pressure in other places is lowered to cause dents. This part of the high pressure residue is also the internal stress of the product. In the ideal state, the temperature of the material rises with the temperature of the mold, the fluidity of the material is good, and the injection also changes to the bottom in the static pressure state.
When changing the molding conditions, the combination of temperature, pressure, and time should be prepared in advance, and the results can be known as early as possible. First, after the time has become very long, it is easy to know the small changes in the pressure. It should be noted that the result when the temperature is changed should be the result after the injection of the material, and then the temperature is lowered and then produced.