How to Set Minimum Walls for Ductile Iron (By Grade)

Table of contents

Why minimum wall is not one number

“Minimum wall thickness for ductile iron” depends on three levers:

• Grade / matrix (e.g., EN-GJS-400-18 vs 700-2): higher strength grades are less forgiving in thin or very heavy sections.
• Process (green sand / resin sand / shell): mould rigidity and surface quality change fill/feeding margins.
• Part size / thermal modulus: small parts shed heat faster; large parts need more wall to fill and feed.

Use the table below to pick a realistic, stable t_min—then apply the design rules in Section 3 to keep it castable.

Quick reference: t_min by grade × process × size

Values are stable continuous wall targets. Local short features can go ~0.5 mm (0.02 in) thinner if well fed. Use mm/in in drawings.

Part envelope

• Small: ≤ 300 mm (12 in) major dimension
• Medium: 300–800 mm (12–31 in)
• Large: ≥ 800 mm (31 in)

Use tips：

• If walls vary widely, size t_min by the thinnest continuous flow path.
• For pressure parts or −40 °C duty, derate one band thicker or choose a ferritic grade.

Design rules that keep thin walls sound

• Uniformity first: keep adjacent-wall ratio 0.7–1.3; avoid instant jumps > 1.5× within 10–15 mm (0.4–0.6 in).
• Ribs: thickness ≤ 0.6–0.7 × wall; taper into parent with fillet radius ≥ 0.5 × wall (absolute ≥ 1.5 mm / 0.06 in).
• Pads/bosses: pad thickness ≈ wall + 1–2 mm (0.04–0.08 in); avoid “plateaus” > 1.5 × wall without taper.
• Draft: externals 0.5–1.0°; internals/cores 1.0–1.5° (shell cores can be slightly lower if ejection allows).
• Holes & webs: minimum cored hole ≥ 1.2 × wall; maintain web ≥ wall between holes.
• Flow direction: feed thin → thick; aim for short, hot flow paths.

Further reading:

Wall Thickness & Uniformity Rules

Fillets & Radii

How grade, section size and matrix interact

• Ferritic grades (e.g., EN-GJS-400-18/450-10) tolerate thinner walls and show better low-temp toughness.
• Pearlitic/higher-strength grades (500-7/700-2) demand more wall or tighter process control to avoid chill and to keep elongation.
• Section size effect: thin sections can over-achieve UTS vs test bars; very heavy sections may under-achieve unless feeding/matrix are controlled.
• Heat treatment: normalizing increases pearlite/strength (watch elongation); ADI changes dimensions post-HT—treat as +0.02–0.06% growth budget.

Cross-reference: Ductile Iron Grades: A536 vs EN-GJS

Process notes: green vs resin vs shell

• Green sand: most economical; higher t_min due to mould compliance and gas; manage compactability/moisture windows to stabilize.
• Resin sand: stiffer mould/core; cleaner surfaces; mid t_min; great for complex cores; control LOI and coating DFT to prevent blows/burn-on. → /resin-sand-vs-green-sand-accuracy-finish
• Shell molding: best thin-wall capability and CT; higher tooling; ensure core spans (L/t) are within limits and support long cores.

What to put on the drawing (copy–paste)

• Material call-out: “EN-GJS-500-7 (ASTM A536 80-55-06 acceptable).”
• Minimum walls: “Continuous t_min = 4.5 mm (0.18 in); local features t_local ≥ 4.0 mm (0.16 in).”
• Transitions: “Ribs ≤ 0.7 × t; fillets ≥ 0.5 × t (min 1.5 mm / 0.06 in).”
• As-cast tolerance: “ISO 8062-3 CT7 (small) / CT8 (mid).”
• Surface: “As-cast Ra 6.3–12.5 µm; sealing faces after machining Ra 1.6–3.2 µm.”
• Stock: faces/ODs +1.5–3.0 mm (0.06–0.12 in); bores by diameter band.
• SC/CC list: identify critical features for PPAP/FAI; specify CMM/3D scan with datum lock.

Worked example (hub bracket, EN-GJS-500-7)

• Size: 420 × 280 × 80 mm (medium). Process: resin sand.
• Draft design: target t_min 5.5 mm (0.22 in); ribs at 0.7 × t; fillets ≥ 3.0 mm (0.12 in).
• Gating: fill from thin spokes to thicker hub; small chills at hub-to-spoke junctions.
• Outcome: no misruns; CT8 achieved; machining stock reduced from 3.0 → 2.0 mm; weight −7%.

What YB Metal delivers

YBmetal Solution validates thin-wall designs with simulation-backed gating, then proves them out with CMM/3D scan:

• Feasibility pack: part-specific t_min, CT band and Ra targets by zone.
• Process plan: green/resin/shell choice with gating/risering and coating DFT windows.
• Evidence: trial reports, microstructure and hardness trends, dimensional layouts (PPAP on request).

Want a yes/no on your thin-wall concept? Upload your drawing via /rfq—YB Metal will return a feasibility note and a quote.