During the injection molding process, shrinkage and depression is a common phenomenon. As a plastic mould maker, we have encountered such a situation in the process of injection molding. We also analyzed the factors of this problem and the main reasons are as follows,

  1. Injection machine
    (1) The injection nozzle hole is too large to cause the melt to recirculate and shrink, and when it is too small, the resistance is insufficient to shrink;
    (2) If the clamping force is insufficient, the flash will also shrink. Check whether the clamping system has any problems;
    (3) If the amount of plasticization is insufficient, a machine with a large amount of plasticization should be used and need check whether the screw and the barrel are worn.
  2. Plastic mould
    (1) The design of the parts wall thickness should be uniform and ensure the shrinkage is consistent.
    (2) The cooling and heating system of the mold should ensure that the temperature of each part is consistent.
    (3) The injection system should be ensured to be unobstructed, and the resistance should not be too large. For example, the size of the main channel, the runner, and the gate should be appropriate, the finish should be sufficient, and the transition zone should have a circular transition.
    (4) For thin parts, the temperature should be raised to ensure smooth flow, and the mold temperature should be reduced for thick-walled parts.
    (5) The gate should be opened symmetrically, as far as possible in the thick part of the part, and the volume of the cold well should be increased.
  3. Plastics materials
    Crystalline plastics shrink than conventional non-crystalline plastics. When processing, the amount of material should be increased appropriately, or a replacement agent should be added to the plastic to accelerate crystallization and reduce shrinkage and depression.
  4. Processing
    (1) The temperature of the barrel is too high, and the volume changes greatly, especially the temperature of the front furnace. For plastics with poor fluidity, the temperature should be properly increased to ensure smoothness.
    (2) The injection pressure, speed, back pressure is too low, and the injection time is too short, so that the amount or density is insufficient, and the contraction pressure, speed, back pressure is too large, and the time is too long, causing the flash to shrink.
    (3) The feeding amount means that the injection pressure is consumed when the cushion is too large, and when the amount is too small, the amount of the material is insufficient.
    (4) For parts that do not require precision, the mold can release it early when the outer layer is basically condensed the hardened while the inner side is still soft, it can be slowly cooled in air or hot water. This can make the shrinkage depression smooth and not conspicuous and does not affect the use.

Micon Mould is a reliable and responsible manufacturer in plastic industry who is also attaches great importance to protecting the intellectual property of their customers.
Professional plastic injection mould manufacturer. Specialized in manufacturing thin wall injection moulds, industrial and agricultural packaging mould, household mould, plastic medical labware moulds etc.
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