Undercut features.
Mold side actions.
Hidden geometry.
Undercut design for injection molded parts. Undercuts trap molded parts in mold. Side actions, lifters, manual operations enable.
Key principles.
Reverse draft
Feature with reverse draft. Trapped in mold without action.
Slides
Mold inserts that move sideways for ejection.
Angled mold pieces
Angled mold pieces lift past undercut during opening.
Bumper, gate cut
Hand-removed gates, snap-fits with manual demolding.
Significant
Each side action 30-60% mold cost premium.
Redesign
Design avoids undercuts when possible. Use draft instead.
FAQ
What is "undercut"?
Feature with reverse draft. Cannot eject from straight-draw mold.
Side actions cost?
30-60% mold cost premium per side action. Avoid where possible.
Lifters?
Angled inserts that lift past undercut during mold opening. Cost similar to side actions.
Manual ejection?
Hand-removed gates, snap-fits. For low-volume.
Undercut alternatives?
Two-piece molded + assembled. Two-shot molding. Snap-fit features hide undercuts.
CNC vs molding?
CNC handles any geometry. Undercuts trivial in CNC. Cost vs molding crossover at volume.
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