Problem:
During cooling, voids form within the wall section of the  moulding. Voids often form instead of sink marks, when the outer layers cool quickly resulting in contraction from within.

Solution:

1. Increase the shot volume.
2. Ensure the non return valve is working.
3. Experiment with hold pressure time to achieve maximum shot weight .
4. Increase the hold pressure.
5. Reduce the temperature of the plastic melt.
6. Reduce the injection speed.
7. Increase the gate size.
8. Check wall thickness around the gate area..
9. Reduce rib or boss thickness.
   

 ImtechDesign.com 

Moldflow Consulting