What are the causes of product cracking during injection molding?

There are several reasons for product cracking during injection molding.
Processing aspect
(1) If the processing pressure is too high, the speed is too fast, the filling volume is high, and the injection and holding time is too long, it will make the internal stress too large and crack.
(2) Adjust the mold opening speed and pressure to prevent the mold release from cracking due to rapid pulling of the workpiece.
(3) Properly raise the mold temperature to make the workpiece easy to demold, and properly lower the material temperature to prevent decomposition.
(4) Prevent cracks caused by degradation of welds due to plastic degradation.
(5) Use mold release agents appropriately, and care should be taken to eliminate aerosols and other substances adhering to the surface of the mold.
(6) The residual stress of the part can be eliminated by annealing heat treatment immediately after molding to eliminate the internal stress and reduce the cracks.
2. For the mold
(1) Balance should be maintained. For example, if the number and cross-sectional area of ejector pins are large enough, the drawing angle should be large enough and the cavity surface should be smooth enough to prevent cracks due to residual stress concentration caused by external forces.
(2) The structure of the workpiece should not be too thin, and the transition part should be rounded as much as possible to avoid the stress concentration caused by sharp corners and chamfers.
(3) Minimize the use of metal inserts to prevent the increase in internal stress caused by the different shrinkage rates of the inserts and workpieces.
(4) Appropriate demoulding inlet channels should be provided for deep bottom parts to prevent vacuum underpressure.
(5) The main channel is large enough to release the gate material for future curing, thus facilitating demolding.
(6) Main channel bushings and nozzle joints should prevent dragging of frozen material to make the part stick to the fixed mold.
3. Material
(1) Excessive recycled material content resulting in low strength parts.
(2) Excessive humidity, causing some plastics to react with water vapor, reducing strength and causing cracking.
(3) The material itself is not suitable for the environment or quality of processing, and contamination can cause cracking.
Different injection molds have different requirements. To sum up, the performance requirements of plastic mold for mold steel are: hardness, polishing, etching performance, welding performance, wear resistance, toughness, dimensional stability, corrosion resistance, etc.