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Troubleshooting Guide Part 2 How to solve the most common problems when injection moulding

In the last article we identified the top 5 most common problems when plastic injection moulding. This week CJ Tool and Mouldings will be looking at the solutions for these problems in order to resolve them.


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Solutions for Distortion


  1. Aim for uniform packing of the mould
  2. Experiment with different temperatures
  3. Ensure balanced filling of the mould
  4. Increase the injection speed
  5. Ensure uniform and symmetrical cooling of the moulding
  6. Choose a more free-flowing plastic material
  7. Consider changing to a material with lower shrinkage
  8. Reduce differences in wall


Solutions for Flash


  1. Ensure the mould is bedded out properly.
  2. Reduce the injection speed.
  3. Reduce the maximum cavity pressure during injection or hold.
  4. Reduce the melt temperature.
  5. Check rigidity of the mould and machine platen.
  6. Check material viscosity is within specification.
  7. Consider running the mould on a machine with higher clamp force.
  8. Check sufficient clamping force has been set.
  9. Check that there is no debris between tool faces holding the tool off.


Solutions for Short Mouldings


  1. Increase the shot volume.
  2. Switch over later from injection pressure to hold pressure.
  3. Increase the injection speed.
  4. Increase the temperature of the melt and mould.
  5. Improve venting at the end of the flow path.
  6. Choose an easier flowing material.
  7. Increase the gate size.
  8. Check the actual wall thickness of the cavity.
  9. Move the position of the gate.
  10. Incorporate flow leaders.
  11. Check for material leaking from nozzle.
  12. Reduce clamping force to allow gas to vent out.


Solutions for Weld or Knit Lines


  1. Increase the injection speed.
  2. Increase the hold pressure.
  3. Increase the melt temperature.
  4. Optimise hold pressure switch over point.
  5. Ensure adequate venting in the region of the weld line.
  6. Increase the mould temperature.
  7. Investigate moving the gate point.
  8. Change master-batch check compatibility.


Solutions Black Specs


  1. Reduce the melt temperature of the Polymer.
  2. Reduce the screw speed and/or back pressure
  3. Clean the moulding machine thoroughly , specifically the hoppers hopper throat.
  4. Check for impurities , leaks or dirt deposits in the feed stock hopper supply.
  5. Check the shot weight. The entire shot weight should not be less than 15-25% of the maximum capacity of the moulding machine.
  6. Check the compatibility of pigment or master-batch with the base polymer.
  7. Reduce the time in which the material is openly exposed to the ambient conditions.



CJ Tool and Mouldings have over 30 years of plastic injection moulding experience. Click to learn more about the 5 most common problems when injection moulding or, if you have any concerns regarding the process please contact us today!


Added: 23 Apr 2019 11:08

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