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Analysis of the cause of the cracking of the injection molding products

release time:2017-12-19 | Article Source:

  Cracking includes cracks, cracks, cracks, whiteness and cracking on the surface of the parts, as well as damage caused by die sticking and flow path sticking. It is demoulding and cracking according to the time of cracking. The main reasons are as follows:


injection molding

  1. aspects of processing:


  (1) excessive processing pressure, faster speed, more charging, injection and longer holding time will cause excessive internal stress and crack.


  (2) adjust the speed and pressure of the open die to prevent the rapid and strong pullout to cause dehiscence and cracking.


  (3) properly adjust the temperature of the mold to make the parts easy to die out, and to properly adjust the temperature of the material to prevent the decomposition.


  (4) to prevent the cracks due to the weld mark and the degradation of the mechanical strength caused by the degradation of plastic.


  (5) properly use the demoulding agent, and pay attention to the frequent elimination of air mist and other substances attached to the surface of the mold.


  (6) the residual stress of the workpiece can be reduced by heat treatment immediately after the molding to reduce the internal stress and reduce the formation of the crack.


  2. aspects of mold:


  (1) the ejection must be balanced, for example, the number and area of the ejector must be enough, the inclination of the ejection must be enough, the cavity surface must be smooth enough, so as to prevent the cracking due to the external force leading to the residual stress concentration.


  (2) the structure of the workpiece can not be too thin, and the transition part should be used as far as possible to use the arc transition to avoid the stress concentration caused by the sharp angle and the chamfering.


  (3) metal inlay is used as little as possible to prevent the increase of internal stress caused by the different shrinkage rate of the embedded parts and the parts.


  (4) a proper demoulding intake passage should be set up for deep bottom parts to prevent the formation of vacuum negative pressure.


  (5) the mainstream road is sufficient for the ambassador's gate not to be cured when it is cured, so that it is easy to die.


  (6) the joint of the main channel sleeve and the nozzle should prevent the drag of the cold hard material and make the parts stick to the fixed mold.


  3. material aspects:


  (1) the content of the recycled material is too high, which causes the strength of the parts to be too low.


  (2) excessive humidity causes the chemical reaction of some plastic and water vapor, reducing the strength and cracking the top out.


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


  4. platform: injection molding machine plasticizing capacity should be appropriate, too small plastic insufficient not fully mixed and brittle, too large will be degraded.