YBmetal has provided our customers with a wide range of thin-walled and thick-walled castings. Engineer’s rulebook for gray/grey and ductile iron: minimum iron casting wall thickness by process, uniformity ranges, rib/fillet/boss ratios, transition design, and machining stock & draft. Includes mm/in tables, simple charts to create, and an RFQ checklist.
- Realistic minimum walls on modern lines:
- Gray iron: 4–6 mm (0.16–0.24 in) in green sand; 3–4 mm (0.12–0.16 in) in shell.
- Ductile iron: 5–7 mm (0.20–0.28 in) in green sand; 4–5 mm (0.16–0.20 in) in shell.
- Uniformity target: adjacent sections vary by ≤ 20–30 %, otherwise add transitions/ribs.
- Ribs vs thick plates: stiffness comes cheaper from ribs; plate thickening creates hot spots.
- CT & stock: specify ISO 8062-3 CT for as-cast, and keep machining allowance 1.0–3.5 mm (0.04–0.14 in) by size/process.
- When to switch process: persistent thin-wall + high accuracy → shell; heavy sections/large parts → resin sand.
Minimum iron casting wall thickness by material & process
| Material | Process | Typical minimum wall* | Notes |
|---|---|---|---|
| Gray/grey iron (EN-GJL / ASTM A48) | Green sand | 4–6 mm (0.16–0.24 in) | Best flow & damping; thin ribs help stiffness |
| Ductile iron (EN-GJS / ASTM A536) | Green sand | 5–7 mm (0.20–0.28 in) | Needs feeding & nodule control; avoid knife edges |
| Gray iron | Shell molding | 3–4 mm (0.12–0.16 in) | Clean surfaces, tight CT; good for thin webs |
| Ductile iron | Shell molding | 4–5 mm (0.16–0.20 in) | Good for thin + accuracy; tooling cost ↑ |
| Gray/Ductile iron | Resin sand | 6–10 mm / 7–12 mm | Stable for large/heavy parts and many cores |
Uniformity rules
Variation limit & step transitions
- Adjacent sections: aim for ≤ 20–30 % thickness change.
- If the change is larger, use a ramp (transition length ≥ 3–5× the wall) or blend with generous radii.
Junctions (T, L, X) and hot-spot control
- At T-junctions, local thickness ≈ 1.2–1.4× wall; add a fillet radius to spread modulus.
- For L/X junctions, add coring or relief pockets to prevent heavy nodes; consider chills where needed.
Ribs, bosses & fillets (stiffness without hot spots)
| Feature | Rule of thumb | Why it works |
|---|---|---|
| Rib thickness | 0.6–0.8 × wall | Stiffness ↑ with less mass; cools uniformly |
| Rib height | 3–5 × wall | Efficient bending stiffness |
| Boss diameter | ≥ 2.0–2.5 × wall | Prevents sink & localized shrinkage |
| Boss thickness | ≈ wall to 1.2 × wall | Avoids hot mass; add under-cuts only if needed |
| Fillet radius (internal) | 0.25–0.5 × wall | Reduces stress & feeding problems |
| Fillet radius (external) | ≥ 0.25 × wall | Mold strength & better flow |
| Cored hole Ø | ≥ 1.5 × wall | Core strength & cleaning access |
Draft, shrinkage, and machining stock (tie to ISO 8062)
- Draft angles: external 1.0–1.5°, internal 1.5–2.0° (green sand); shell can be lower.
- Shrinkage allowance (pattern): gray 0.8–1.0 %, ductile 1.0–1.2 %.
- Typical machining allowance (both units):
- Specify: as-cast features → ISO 8062-3 CT grade; machined features → GD&T with datum strategy.
| Rough weight | Green sand | Resin sand | Shell |
|---|---|---|---|
| ≤ 5 kg (≤ 11 lb) | 1.0–1.5 mm (0.04–0.06 in) | 1.5–2.0 mm | 0.8–1.2 mm |
| 5–20 kg (11–44 lb) | 1.5–2.5 mm (0.06–0.10 in) | 2.0–3.0 mm | 1.0–1.5 mm |
| ≥ 20 kg (≥ 44 lb) | 2.5–3.5 mm (0.10–0.14 in) | 3.0–4.0 mm | 1.5–2.0 mm |
Iron Casting Wall Thickness strategies that actually work
- Replace plate thickness with ribs; keep rib-to-wall ratios in table above.
- Spread thickness changes with long blends; avoid abrupt steps and sharp corners.
- Vent the hardest-to-fill areas; add chill/sleeve only where modulus demands.
- Control melt & sand: pouring temp window, inoculation, AFS GFN/moisture/LOI control.
- Validate early: pilot cast + FAI/CMM / 3D scan on the thinnest paths.
When to switch process (green vs resin vs shell)
- You require ≤ 4 mm gray or ≤ 5 mm ductile with tight CT → Shell molding.
- You have large/heavy geometry or many cores → Resin sand for dimensional stability.
- You target volume, moderate accuracy → Green sand for best piece-price.
YBmetal provides Quality & verification plans for iron casting products
- Metallurgy: spectrometer per heat; Brinell hardness per batch; ductile: nodule count/shape.
- Dimensional: FAI + CMM; 3D scan on thin-wall regions; gauge R&R on critical datums.
- Defects control: monitor scrap by reason (misrun, porosity, shrink), apply root-cause (feeding, coating, venting).
- Records: pouring temp, yield, sand KPIs; traceability heat/batch/serial with photo logs.
RFQ checklist (send with drawings)
- Annual volume & batch size; target process (green/resin/shell).
- Material & grade (e.g., EN-GJL-250 / EN-GJS-500-7).
- Minimum wall targets & tight areas; preferred CT grade; draft and machining datum plan.
- Leak/NDT requirements; PPAP level; sampling plan.
- Coating/packaging; destination.
- Any prior rejects/risks you want solved.
FAQs
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