DIII Process and Part Dimensions…

During an on-site consultation, I was recently asked this question…

When troubleshooting a Decoupled III process for variations in overall part dimensions, what parameters should we investigate.

note: A DIII process has many specific attributes, but the key aspects include a velocity controlled 1st stage fill (90%), 1st to 2nd stage transfer by position, velocity controlled 2nd stage pack, 2nd to 3rd stage transfer on cavity pressure at the gate, and 2rd stage hold by pressure control.
My Response
The parameters and process outputs which affect part size in a DIII process are commonly:
  • Melt Tempertaure
  • Transfer Setpoint
  • Packing Speed
  • Hold Pressure
  • Mold Temperature
Additional Thoughts

One of the best ways to approach dimensional issues with a DIII process, would be to compare the pack rate and cooling rate to the documented standard and return them to the standard. These are the upward and downward slopes of the in-cavity pressure curves representing the rate of packing and cooling within the cavity.


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