Iron casting cost: most quotes rise or fall on four levers: metal, sand, energy, and labor. This playbook explains what drives each, how to estimate them in $/kg and $/lb, and what to change on your print and process to cut waste—without risking quality.
The cost formula (simple & practical)
Price per net kg (or lb) ≈
Metal/yield + Sand/consumables + Energy + Direct labor + Overhead + Machining + Finishing/NDT + Profit.
Where:
- Yield = net casting weight ÷ poured weight (runners + risers + returns).
- Buy‑to‑fly (BTF) = 1 / yield. If yield = 60%, BTF ≈ 1.67 (you buy 1.67 kg to ship 1 kg).
- Currency & units: show both $/kg and $/lb (1 kg = 2.2046 lb).
Driver 1 — Metal (typically the largest share)
What moves it
- Grade (gray/grey vs ductile, alloyed vs standard), CE/Si/Mn windows.
- Market index for scrap/pig iron; surcharge for alloy additions.
- Yield/BTF: gating/riser design, hot‑spot control, pattern layout, core prints.
Typical impact
- Share of piece price: 45–65% (green sand), 40–60% (no‑bake/shell).
- Yields (indicative): Green sand 55–75%, No‑bake 50–70%, Shell 60–80% (geometry dependent).
Actions that save
- Consolidate wall transitions & add radii ≥ 3–5 mm (0.12–0.20 in) to raise yield.
- Use exothermic/insulating risers + chills; simulate solidification before cutting tooling.
- Agree material ranges (e.g., ASTM A536 grade family) to avoid unnecessary alloy surcharges.
Driver 2 — Sand & consumables
What moves it
- Process route (green sand / no‑bake / shell), core count & volume, molds per hour.
- Binder, catalyst, coating, sleeves, filters, chills, shot/grit for cleaning.
Typical usage per net 1 kg (2.2 lb)
| Process | Returnable sand use | New sand/binder | Notes |
|---|
| Green sand | 6–10 kg circulation | Minimal new sand; additives | Low cost; high reuse |
| No‑bake | 3–6 kg mix | 1.0–1.8 kg sand + resin | Better accuracy/cores |
| Shell | 1–2 kg shell | 0.6–1.0 kg resin‑coated sand | Best finish; higher material cost |
Actions that save
- Fewer cores with design‑for‑moldability; combine cores or switch to shell where justified.
- Standardize riser sleeves/filters to purchased part numbers; buy at volume.
Driver 3 — Energy
What moves it
- Furnace type (coreless induction vs cupola), kWh per melt/hold, preheat and cure.
- Pour superheat window, scrap moisture (drying), and machining power.
Typical energy (indicative)
| Step | kWh per net kg | kWh per net lb |
| Melt & hold | 0.6–1.0 | 0.27–0.45 |
| Molding/cure | 0.1–0.3 | 0.05–0.14 |
| Cleaning/machining | 0.1–0.2 | 0.05–0.09 |
Actions that save
- Narrow the pour temperature band; avoid excessive superheat.
- Batch parts to reduce idle hold; schedule energy‑heavy jobs off‑peak.
- Use insert tooling to cut machining time & power.
Driver 4 — Labor
What moves it
- Pattern changeover, core‑making steps, mold handling, cleaning, machining minutes, inspection & packing.
- Learning curve from sample to rate.
Benchmarks (indicative)
| Operation | Minutes per net kg | Minutes per net lb |
| Molding & core | 0.5–1.2 | 0.23–0.54 |
| Cleaning/fettling | 0.2–0.6 | 0.09–0.27 |
| Machining (simple) | 0.4–0.8 | 0.18–0.36 |
| Machining (complex) | 0.8–1.8 | 0.36–0.82 |
Actions that save
- Reduce machining stock to realistic levels (see table below).
- Combine operations with datums for single‑setup machining.
- Use fixtures & Poka‑Yoke to lower rework minutes.
What to change on the drawing to lower the price
- Tolerances: Match process ISO 8062‑3 capability (see CT grades).
- Surface finish: Don’t over‑spec; Ra 3.2–6.3 μm (125–250 μin) is typical for machined faces.
- Machining allowance: Use realistic stock by mass range (below).
- Uniform walls & radii: R ≥ 3–5 mm (0.12–0.20 in); avoid sudden transitions.
- Critical‑to‑quality features: Call them out so checks focus where value is.
Table — Typical capability & allowances
| Item | Green sand | No‑bake | Shell |
| ISO 8062‑3 CT grade | CT9–CT10 | CT8–CT9 | CT6–CT7 |
| 100 mm linear tol (indicative) | ±1.6–2.4 mm (±0.063–0.094 in) | ±1.2–1.8 mm (±0.047–0.071 in) | ±0.6–1.0 mm (±0.024–0.039 in) |
| Machining stock (5–10 kg) | 1.5–2.5 mm (0.06–0.10 in) | 1.2–2.0 mm (0.05–0.08 in) | 0.8–1.5 mm (0.03–0.06 in) |
Sample calculations (plug‑and‑play logic)
Scenario A — 10 kg (22 lb) gray iron valve body, green sand
- Yield 65% → BTF 1.54.
- Metal $/kg = $0.95; metal per net kg = $1.46.
- Sand/consumables = $0.18/kg; Energy = $0.12/kg; Direct labor = $0.40/kg.
- Cleaning/machining/NDT/overhead/profit (bundle) = $0.90/kg.
- Indicative price ≈ $3.06/kg ($1.39/lb).
Scenario B — 50 kg (110 lb) ductile iron pump housing, no‑bake
- Yield 58% → BTF 1.72.
- Metal $/kg = $1.15; metal per net kg = $1.98.
- Sand/consumables = $0.35/kg; Energy = $0.18/kg; Direct labor = $0.62/kg.
- Cleaning/machining/NDT/overhead/profit (bundle) = $1.30/kg.
- Indicative price ≈ $4.43/kg ($2.01/lb).
These are illustrative. Your quote will reflect grade, geometry, tooling amortization, inspection plan, and batch size.
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