Cracking, including thread-like cracks, micro-cracking, top white, cracking on the surface of the part, or trauma crisis caused by sticking of the part and sticking of the flow channel, demoulding cracking and application cracking according to the cracking time. There are mainly the following reasons:

　　1. Processing:

　　If the processing pressure is too high, the speed is too fast, the filling is more, the injection and holding time are too long, it will cause excessive internal stress and crack.

　　Adjust the mold opening speed and pressure to prevent the mold from being cracked due to rapid and strong drawing.

　　Properly adjust the temperature of the mold to make the parts easily demolded, and appropriately lower the temperature of the material to prevent decomposition.

　　Prevent cracking due to the deterioration of the plastic caused by the welding line and the degradation of the plastic.

　　Appropriate use of release agent, pay attention to often eliminate the aerosol and other substances attached to the mold surface.

　　The residual stress of the workpiece can be reduced by the annealing and heat treatment immediately after forming to eliminate the internal stress.

　　2. Mold aspect:

　　Ejection should be balanced. For example, the number of ejector rods and cross-sectional area should be sufficient, the draft angle should be sufficient, and the cavity surface should be smooth enough to prevent cracking due to the concentration of ejection residual stress caused by external forces.

　　The structure of the parts should not be too thin, and the transition part should use arc transition as far as possible to avoid stress concentration caused by sharp corners and chamfers.

　　Minimize the use of metal inserts to prevent the increase in internal stress caused by the difference in shrinkage between the insert and the part.

　　Appropriate demolding air inlet holes should be set for deep bottom parts to prevent the formation of vacuum negative pressure.

　　The mainstream channel is enough to allow the gate material to be demolded in the future, so it is easy to demold.

　　The joint between the main liner bushing and the nozzle should prevent the drag of the chilled material and make the workpiece stick to the fixed mold.

　　3. Material:

　　The content of recycled materials is too high, resulting in low strength of the parts.

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

　　The material itself is not suitable for the processing environment or the quality is poor, and contamination will cause cracking.

　　4. Machine 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.