Problem:
The plastic moulding has sections missing, usually in regions remote from the sprue or in thin-walled regions, because the mould was not completely filled. Possible causes are that too little polymer was metered in, the nonreturn valve is leaky, the pressure was too low or the filling resistance was too great. Filling resistance is made up of contributions from viscosity, runner length and wall thickness.

Solution:

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 to reduce pressure .
11. Check for balanced filling.

 ImtechDesign.com 

Moldflow Consulting