Bosses, Ribs & Fillets: Key Features in Die-Cast Part Design

Designing parts for high-pressure die casting requires balancing function with manufacturability. Among the most critical design features are bosses, ribs, and fillets—each contributing to strength, stability, and ease of casting.

Here’s how to design them right:

🟢 Bosses

Purpose: Mounting points, support pillars, or holes for fasteners/inserts.

Best Practice:

• Keep wall thickness 60–80% of nominal wall to avoid shrinkage

• Add fillets at base to reduce stress concentration

• Ensure ejector pin support behind bosses for clean release

🔵 Ribs

Purpose: Add structural stiffness without adding bulk

Best Practice:

• Rib thickness 40–60% of nominal wall

• Include draft angles (~1.5°) for clean ejection

• Space ribs properly to avoid hot spots or flow blockages

🟠 Fillets

Purpose: Distribute stress and improve metal flow

Best Practice:

• Use minimum 1mm fillet radius in internal corners

• Avoid sharp intersections, especially where ribs meet bosses or walls

• Larger fillets help reduce porosity and improve fatigue life

Neglecting these small but critical features can result in voids, sink marks, or even premature tool wear. But when designed correctly, they contribute significantly to casting efficiency and part longevity.

At LVIO Precision, we review every customer model with manufacturability in mind. We’ll suggest improvements to your boss/rib layout and ensure your part is optimized for both casting and machining—without inflating tooling cost.