Cast iron is one of the most-machined materials in production shops. Graphite particles dull standard tools quickly, and dust generation requires specific coolant strategy.
Cast Iron Types
- Gray cast iron (GG-25, GG-30) — Brittle, free-cutting, abrasive dust
- Ductile (nodular) iron (GGG-50, GGG-60) — Tougher, steel-like
- Compacted graphite iron (CGI) — Modern engine blocks, harder on tools
End Mill Selection
| Type | Best For | Coating |
|---|---|---|
| Solid carbide 4-flute | General gray iron, ≤1.5×D depth | TiAlN or AlCrN |
| Solid carbide 6-flute | High-MRR finishing | AlCrN |
| Indexable face mill | Large flat surfaces | K-grade insert (CVD Al2O3) |
| Ceramic insert mill | CGI, hardened cast iron above 30 HRC | Si3N4 ceramic |
Coating Choice
AlCrN outperforms TiAlN above 800°C cutting temperature. For premium production, CVD multilayer with Al2O3 outer (e.g., Sandvik GC3220) gives 30-50% longer life than PVD.
Cutting Parameters
Starting parameters for 12mm 4-flute carbide end mill in GG-25:
- Vc: 180-250 m/min
- Feed/tooth: 0.10-0.15 mm
- Axial depth: 1×D
- Radial depth: 50-75%D
Coolant Strategy
Most cast iron is machined DRY in production. Coolant + iron dust = abrasive sludge that destroys tools. Air blast for chip evacuation is preferred.
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