Analysis of Cracking in Injection Molding

A、 Processing technology:

1. Excessive processing pressure, fast speed, more material filling, long injection and holding time can all cause excessive internal stress and cracking;

2. Adjust the mold opening speed and pressure to prevent cracking caused by rapid pulling of the parts during demolding;

3. The injection pressure is too low or the injection speed is too fast;

4. Prevent cracking caused by reduced mechanical strength due to fusion marks and plastic degradation;

5. Properly use release agents and pay attention to regularly eliminating aerosols and other substances attached to the mold surface;

6. Residual stress in the workpiece can be eliminated and crack formation reduced by immediately conducting annealing heat treatment after forming;

7. No lubrication or lubrication but poor effect;

8. Adjust the mold temperature appropriately to make the parts easier to demold, and adjust the material temperature appropriately to prevent decomposition;

9. During product production, uneven cooling and shrinkage of plastic in the mold cavity, as well as unreasonable product structure design, can easily cause various defects in the product;

10. Poor plasticization, that is, the melt cannot be uniformly melted;

B. Material quality:

1. The content of regenerated material is too high, resulting in low strength of the parts;

2. Excessive humidity can cause some plastics to undergo chemical reactions with water vapor, reducing their strength and leading to bursting and cracking;

3. Impurities or regenerated materials in raw materials exceed the standard;

4. Excessive moisture content in raw materials;

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

6. Volatile compounds in raw materials exceed the standard;

C. Mold precision:

1. The ejection should be balanced, the cross-sectional area should be sufficient, the demolding slope should be sufficient, and the cavity surface should be smooth enough to prevent cracking due to residual stress concentration caused by external forces;

2. The structure of the component should not be too thin, and the transition part should be rounded as much as possible to avoid stress concentration caused by sharp corners and chamfers;

3. Minimize the use of metal inserts to prevent increased internal stress caused by differences in shrinkage rates between the inserts and the components;

4. The imperfect molding process is mainly manifested in the poor internal quality of convex and concave forging blanks, problems with heat treatment technology and processes, resulting in incomplete quenching of convex and concave molds, soft spots, and uneven hardness;

5. Appropriate demoulding air inlet holes should be set up for deep bottom components to prevent the formation of negative vacuum pressure;

6. The main channel is large enough to demold the sprue material before it has solidified, making it easier to demold;

7. The connection between the main channel liner and the nozzle should prevent the dragging of cold hard materials from sticking to the fixed mold;

8. The structure of the punching die is unreasonable. The slender convex mold is not designed with reinforcement devices, and the discharge port is not smooth, resulting in accumulation. The excessive unloading force intensifies the convex mold's ability to withstand alternating loads;

9. The mold temperature is too low and the fluidity of the melt is too poor;