Solid thick plate region
- Long cooling and sink on opposite face
- Higher resin use per part
- Simple CAD but expensive in production
DFM
Coring Out Thick Sections: Injection Molding Design Rules
Coring out hollows thick sections so ribs carry stiffness without solid plastic mass.
DFM
Coring out removes plastic mass without losing function
Thick sections become shells supported by ribs.
Coring reduces sink, cycle time, and weight on large housings and covers.
Shell stiffness still needs ribs or geometry so the part does not flex in service.
Internal cores must draft toward the same pull direction or use collapsible details.
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 block versus cored shell
The mold sees the same choice as the part designer.
Cored shell with rib frame
- Shorter cycle on many programs
- Lower sink risk
- More CAD work up front
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 articleThick section design
Thick island context.
Thick section designRib design
Stiffness after coring.
Rib designCooling line layout
Cooling follows mass.
Cooling line layoutVisual 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
Coring questions
Does coring weaken the part?
Only if ribs are missing. Design stiffness explicitly after coring.
Can coring be added after T1?
Major coring changes rework steel. Core in CAD before cut.
Do cores need vent paths?
Closed internal cores still need air escape during fill.
Next step
Show cored sections on CAD
Upload section views through thick regions before quoting steel.