DFM & Plastic Part Design
Ribs and Bosses Design for Injection Molding
Design ribs, gussets and screw bosses for stiffness and assembly while managing sink, filling, draft and local stress.
Short Answer
What engineers need to know
Ribs and bosses should add stiffness or assembly function without becoming thick material masses. Their thickness, height, draft, radii, spacing and connection to the nominal wall should be reviewed together.
Keep local mass controlled
Add draft and root radii
Support bosses without heavy intersections
Validate fastening loads
Use ribs for stiffness
Ribs can improve bending stiffness without uniformly thickening the part, but poor proportions can create sink, difficult filling or tool-access problems.
Design bosses around the assembly
Boss geometry depends on screws, inserts, torque, mating parts and load path. Unsupported tall bosses are vulnerable to deformation and breakage.
Check mold access and ejection
Deep, narrow features require adequate steel, venting, draft and reliable release.
Continue the Engineering Review
Related Topics & Project Evidence
Engineering FAQ
Questions about ribs & bosses design
When should ribs & bosses design be reviewed?
Review ribs & bosses design before detailed mold design and steel cutting, while product geometry and tooling decisions can still be discussed efficiently.
Can one rule be applied to every ribs & bosses design project?
No. Resin, part geometry, appearance, tolerance, production volume and molding conditions must be evaluated together for the specific project.