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Lifters: Injection Molding Design Rules
Lifters release internal undercuts during ejection at an angle to mold open.
DFM
Lifters angle internal steel to release hidden undercuts
Internal snaps and hooks often need lifters instead of external slides.
Lifters move at an angle during ejection to pull steel out of internal hooks.
Lifter marks and wear show on high volume programs if geometry is too aggressive.
Snap fits designed for lifter release need draft on lifter contact faces.
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.
Snap and hook review
Lifter friendly internal features
Share these with mold design early.
Undercut depth and draw angle on internal hook
Material choice for snap deflection
Expected cycle count or volume class
Hidden face acceptance for lifter witness
Related rules
Design guide
Jump to sibling rules before you freeze CAD.
DFM article
Long form engineer guide.
DFM articleCantilever snap fit
External snap alternative.
Cantilever snap fitUndercuts
Map all pull conflicts.
UndercutsSide actions
External undercut option.
Side actionsVisual 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
Lifter questions
Are lifters the same as slides?
Slides move perpendicular to open direction. Lifters angle with ejection.
Can lifters be avoided?
Often by splitting the part or changing hook geometry.
Do lifters limit resin choice?
Brittle resins may not tolerate aggressive snap deflection.
Next step
Design snaps with mold release in mind
Upload CAD hooks and internal undercuts for DFM review.