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    Discussion in 'Plastic moulding' started by MIA WANG, Nov 8, 2021.

    1. MIA WANG

      MIA WANG Member

      Joined:
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      1. Processing aspects:

      (1) Excessive processing pressure, too fast speed, more filling, too long injection molding and pressure holding time will cause excessive internal stress and cracking.

      (2) Adjust the speed and pressure of mold opening to prevent mold release and cracking caused by rapid forced drawing.

      (3) Properly increase the mold temperature to make the part easy to demould, and appropriately lower the material temperature to prevent decomposition.

      (4) Prevent cracking due to weld marks and degradation of plastics, resulting in lower mechanical strength.

      (5) Appropriate use of mold release agents, and pay attention to frequently removing substances such as aerosol attached to the mold surface.

      (6) The residual stress of the part can be eliminated by annealing and heat treatment immediately after forming to reduce the generation of cracks.

      2. Mold aspect:

      (1) The ejection should be balanced, such as the number of ejector pins, the cross-sectional area should be sufficient, the demolding slope should be sufficient, and the cavity surface should be smooth enough, so as to prevent the residual stress concentration and cracking caused by the external force.

      (2) The structure of the part should not be too thin, and the transition part should adopt arc transition as much as possible to avoid stress concentration caused by sharp corners and chamfers.

      (3) Minimize the use of metal inserts to prevent the internal stress from increasing due to the difference in shrinkage between the insert and the workpiece.

      (4) Appropriate demoulding air inlets should be provided for deep-bottomed parts to prevent the formation of vacuum negative pressure.

      (5) The main runner is sufficient to allow the gate material to be demolded when it is cured in the future, so that it is easy to demold.

      (6) The sprue bushing and the nozzle should be prevented from being dragged by the chilled material to make the parts stick to the fixed mold.

      3. Material aspect:

      (1) The content of recycled materials is too high, causing the strength of the parts to be too low.

      (2) Excessive humidity causes some plastics to chemically react with water vapor, reducing the strength and causing ejection cracking.

      (3) The material itself is not suitable for the processing environment or the quality is not good, and it will cause cracking if it is polluted.

      4. For the machine:

      The plasticizing capacity of the injection molding machine should be appropriate. If it is too small, it will become brittle due to insufficient plasticization. If it is too large, it will degrade.


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