First, the cause of the dent

1-1 portions of different thickness products

1-2 insufficient internal mold pressure

1-3 mold cooling is not sufficient

1-4 due to insufficient cooling time deformation generated

Second, the knowledge associated

2-1 products in the production process, the occurrence of undesirable phenomena dent is the highest frequency of occurrence in plastic injection mold cooling volumetric shrinkage, early cooling part is the first surface hardening, the internal will produce bubbles, called dents, is slow cooling produced a conspicuous part of the concave surface in the direction of contraction of the bubble.

2-2 large shrinkage materials are also prone to dents. When you want to change the molding conditions to eliminate dents, you should set conditions to set a small contraction direction. That die temperature, reducing the cylinder temperature, injection pressure is increased, it should be noted this may cause internal residual stress.

2-3 Because dent unobtrusive as well, so if you do not affect the appearance, there was intentional on the mold into the appearance of corrosion, such as striated, granular and so on. Also, if the molding material is HIPS, by lowering the mold temperature to reduce the roughness is also effective. However, these methods once a dent occurred, wanted to repair polished products have difficulties.

Third, the method of settlement

3-1 IM: increase injection pressure, injection prolonged dwell time, reduce barrel temperature and mold temperature in the dent where forced cooling.

3-2 short: In the dent where complement upstream side (Figure A). Dent in the materials through the side where there is a small place when this part of the edge thickness (Figure B).

3-3 long-term: the design should completely avoid differences in product thickness. Prone to dent the ribs, elongated shape should be as short as possible

Four differences in material

4-1 large molding shrinkage material, dents also large. Such as PE, PP, even just a little in the ribs, it will have a dent.

V. References:

When the temperature is lowered to 5-1 when not dent, if there is pressure in the cavity of the material should be considered to not have a dent. Material surrounding the pressure within the mold in the mold, i.e., static pressure, are not necessarily wherever. Near the gate portion of the high pressure, if the material through the edge width, because the pressure to pass every corner of the pressure away from the gate near the gate of the same place with all the pressure difference is very small compared to the difference will not generate recess mark, will also be able to obtain an internal residual stress products. The part of the material flows into difficulties in place, this place has a high pressure, the pressure will be reduced elsewhere dent. This part of the high-pressure residual internal stress is also large articles. In an ideal state of the material with a temperature rise of the mold temperature, material flow better, and shot in static state becomes the bottom.

5-2 when the change molding conditions, temperature, pressure, time should be a combination of pre-made forms, according to the order, we can know the results early. First time becomes long, the small changes whenever pressure is also easy to understand. It should be noted: the results obtained when the temperature changes, it should be expected after the injection, the temperature is lowered and so the results after the time of production.