The main reasons for product cracking in injection moldingare as follows:
1. Processing
(1) Too high processing pressure, too fast speed, more filling materials, too long injection and pressure holding time will cause excessive internal stress and cracking.
(2) Adjust the opening speed and pressure to prevent the quick drawing of parts from cracking.
(3) Properly adjust the mold temperature to make the parts easy to demould, and properly adjust the material temperature to prevent decomposition.
(4) Prevent cracking due to low mechanical strength caused by fusion marks and plastic degradation.
(5) Proper use of mold release agent, pay attention to the regular elimination of the air mist and other substances attached to the mold surface.
(6) The residual stress of parts can be eliminated by annealing treatment immediately after forming to reduce the formation of cracks.
2. Mold
(1) The ejection should be balanced, such as the number and cross-sectional area of ejector rods, the angle of demoulding should be enough, and the cavity surface should be smooth enough, so as to prevent cracking due to the concentration of ejection residual stress caused by external force.
(2) The structure of the part shall not be too thin, and the transition part shall adopt arc transition as far as possible to avoid stress concentration caused by sharp angle and chamfer.
(3) Use less metal inserts as far as possible to prevent the internal stress from increasing due to the different shrinkage rate of inserts and workpieces.
(4) For the deep bottom parts, a proper demoulding air inlet channel shall be set to prevent the formation of vacuum negative pressure.
(5) The sprue is enough to release the mold before the material solidifies, so it is easy to release the mold.
(6) The connection between the main channel Bush and the nozzle should prevent the dragging of the cold and hard materials and make the workpiece stick to the fixed mold.
3. Material
(1) The recycled material content is too high, resulting in low strength of the parts.
(2) The humidity is too high, which causes some plastics to react with water vapor, reduces the strength and causes ejection cracking.
(3) The material itself is not suitable for the environment being processed or the quality is not good, and it will crack if it is polluted.
