Stringing or drool at gate
- Gate region overheated or undersized
- Slug not captured at runner end
- Material lot or moisture interaction
DFM
Cold Slug Wells: Injection Molding Design Rules
Cold slug wells trap frozen runner tips to stabilize the next shot at the gate.
DFM
Cold slug wells catch frozen runner tips at the end of fill
They reduce stringing and drool at the next shot on cold runner tools.
Slug wells are small pockets at the runner end that accept the first frozen slug.
Poor slug control shows as stringing, drool, or material degradation at the gate.
Part geometry rarely shows slug wells directly, but fill issues trace back to runner end design.
DFM
Quote this rule with your CAD upload
NetProto DFM review flags these geometry patterns before steel is ordered.
- Call out draw direction and cosmetic faces on the model.
- Note resin family even when the grade is not final.
- Tighten tolerances only on mating features that need them.
Process
Clean runner end versus stringing at gate
T1 photos of the gate region shorten debugging.
Stable slug break
- Slug well sized for resin and shot
- Gate freeze timing matched to pack
- Consistent de gate or robot handling
Related rules
Design guide
Jump to sibling rules before you freeze CAD.
Design guide hub
All DFM topics on one route.
Design guide hubDFM article
Long form engineer guide.
DFM articleRunner design
Layout context.
Runner designSprue glossary
Upstream feed path.
Sprue glossaryGate types
Gate style interaction.
Gate typesVisual reference
Molding context for this rule
Images from the Forge media library illustrate typical programs.
Injection molded part design review on CAD
Injection molded part design review on CAD
Plastic housing with ribs and bosses
Plastic housing with ribs and bosses
Engineer measuring molded component
Engineer measuring molded component
FAQ
Cold slug questions
Are slug wells visible on the part?
No. They live in the runner steel, not on the component.
Do hot runners use slug wells?
Hot systems use different tip management. Cold runners use slug wells often.
Can stringing be fixed after T1?
Process and steel tweaks are possible within qualified program scope.
Next step
Share gate region photos from T1
Upload CAD and sample photos when stringing appears at the gate.