What is the reason for cracking of injection molded products?


When the injection mold is produced, cracking occurs, i […]

When the injection mold is produced, cracking occurs, including filamentous cracks on the surface of the product, micro-cracks, top white and product loss. According to the cracking time, it is divided into demolding cracking and application cracking, which are mainly caused by the following aspects.

1. The processing pressure is increased, the speed is too fast, the injection of too much material, and the pressure holding time is too long, which will cause excessive internal stress and cracking
2. Adjust the mold opening speed and pressure to prevent the product from being pulled out quickly and cracked.
3. Properly increase the mold temperature to make the product easy to demould, and appropriately lower the material temperature to prevent decomposition.
4. Prevent cracking due to weld line and plastic degradation caused by lower mechanical strength.
5. Appropriately use the release agent, and pay attention to often eliminate the aerosol and other substances attached to the film surface.

1. The ejection should be balanced, the number of ejector pins, the cross-sectional area should be sufficient, the ejection slope should be sufficient, and the cavity surface should be smooth enough to prevent cracking due to the concentration of residual stress in the ejection caused by external force.
2. The product structure should not be too thin. The transition department should use transition as much as possible to avoid stress concentration caused by sharp corners and chamfering.
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 product.
4. The main channel is enough to make the gate material demould before curing, which is convenient for demoulding.

③Machine aspect
The plasticizing capacity of the injection molding machine should be appropriate. If the plasticizing capacity is too small, it will not be fully mixed and become brittle. If it is too large, it will degrade.