Ribs.
Stiffening features.
Without thick walls.
Plastic part rib design. Ribs add stiffness without thick walls (which cause sink marks). Specific rules for rib thickness, height, draft, fillets.
Key principles.
60% wall
Rib 60% of base wall. Prevents sink marks at rib base.
3× wall max
Rib height ≤ 3× wall thickness. Above this, draft and shrinkage issues.
0.5° per side
Standard 0.5° draft per side. Allows ejection from mold.
0.25× wall
Generous fillet at rib base reduces stress concentration.
3× wall
Rib center-to-center 3× wall thickness minimum.
Significant
Rib pattern stiffness 2-5× plain plate. Without weight or sink marks.
FAQ
Why use ribs?
Add stiffness without thick walls. Thick walls cause sink marks. Ribs solve this.
Cross vs parallel ribs?
Cross ribs (X pattern) gives 2-3× stiffness vs parallel. Choose per loading direction.
Rib spacing rules?
Center-to-center 3-5× wall thickness. Tighter spacing = stiffer but more material.
Sink mark prevention?
Rib thickness 60% of wall = critical rule. Going thicker causes sink. Fillet base helps.
Demolding?
Sufficient draft (0.5° each side) and fillets. Rib must release cleanly from mold.
Composite ribs?
Cross-rib + edge stiffening + thickness optimization for max stiffness per material.
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