Solid thick pillar
- Sink on the opposite wall
- Long cycle waiting on core heat removal
- Void risk in the center of thick sections
DFM
Thick Section Design: Injection Molding Design Rules
Thick plastic sections drive sink, voids, and long cycles unless you core them.
DFM
Thick sections buy stiffness with sink and cycle cost
Solid bosses and thick islands are the fastest way to fail cosmetics.
Thick plastic holds heat. Cooling time and sink risk rise faster than structural benefit.
Coring out thick regions keeps nominal wall while preserving stiffness through ribs.
NetProto flags thick sections that will pull sink to the opposite cosmetic face.
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.
Mass
Solid thick block versus cored section
The mold sees steel temperature and pack pressure, not your intent label.
Cored or ribbed section
- Nominal wall with rib grid
- Boss tied to wall with coring through the center
- Faster cooling path to the cavity surface
Drawing notes
Thick section review inputs
Mark these before T1 samples surprise you.
Cosmetic face opposite thick bosses
Section views through suspected thick islands
Coring preference if already modeled
Resin grade if glass filled or high shrink
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 articleBoss design
Thick pillars for fasteners.
Boss designUniform wall thickness
Gradual transitions away from thick islands.
Uniform wall thicknessRib design
Stiffness without thick walls.
Rib designVisual 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
Thick section questions
Will sink always show on thick bosses?
Not guaranteed, but uncored bosses on thin cosmetics are a top sink driver.
Can thick sections be gated directly?
Often yes for pack, but cosmetics and weld lines still need a plan.
Should I avoid thick sections entirely?
No. Control them with coring, ribs, and gradual transitions.
Next step
Fix thick sections before steel
Upload CAD with section views through bosses and thick regions.