Unstable cushion

[chrisprocess]

Decompression as well as wet material comes to mind.

Also if your nozzle ID is too small your cushion will bounce - especially with hot-runner tool. Difficult to get consistent pressure/times/speeds through your a tight nozzle, through the hot-runner, into your (small?) gates, and then into your full cavities.

See how much injection pressure you use at the nozzle by doing an air-shot -
or if you want to be more thorough you can do a pressure loss study to see where all pressure is going through your system

[Filiberto]

We finally fixed the variation with a new screw and barrel.

[Suhas]

Thanks for letting us know Filiberto. This helps us learn!
Thanks,
Suhas