Mold and die work is the most demanding hardened-steel machining. Final cavity finishing in 50-65 HRC tool steels demands the right tools.
Common Mold Steels
| Steel | Hardness | Use |
|---|---|---|
| P20 (annealed) | 30 HRC | Plastic injection molds (pre-hardened) |
| P20 (heat treated) | 40 HRC | High-volume injection molds |
| H13 | 50-54 HRC | Hot-work die casting, forging |
| D2 | 58-62 HRC | Cold-work dies, blanking |
| S7 | 54-56 HRC | Shock-resistant dies |
| M2 HSS | 62-65 HRC | High-speed steel cutters |
Roughing Hardened Steel (above 45 HRC)
- Solid carbide nano-coated end mills (nACo, AlTiCrN)
- Maximum 4×D L:D for rigidity
- Light radial engagement (5-15%) — HSM toolpaths only
- Speeds: 80-150 m/min, feeds 0.05-0.15 mm/tooth
Finishing Hardened Steel
- Ball-end carbide — Standard for 3D cavity finishing
- CBN ball-end — Above 55 HRC, premium finish
- Diamond-coated — Special for P20 + glass-filled plastic abrasion
EDM as Alternative
For sharp internal corners and complex geometries impossible to mill:
- Sinker EDM — Custom electrode shapes, finest detail
- Wire EDM — Through-cuts in any hardness, ±0.005mm
- Hole-pop EDM — Start holes for wire EDM
Surface Finish Strategy
| Surface | Ra Target | Method |
|---|---|---|
| Cooling channels | 3.2 µm | Drilled |
| Ejector pin holes | 0.8 µm | Reamed |
| Cavity walls (visible) | 0.1-0.4 µm | Polished after EDM/mill |
| Cavity surface (matte) | 1.6 µm | EDM finish |
| Parting line | 0.4-0.8 µm | Hand polished |
Tool Brands for Mold Work
- Sandvik CoroMill Plura — Solid carbide for hardened steel
- Mitsubishi MS Plus — Cobalt-chromium tool steels
- NS Tool — Japanese mold-specialty end mills
- Hitachi Epoch — Long-reach hardened steel
Critical: No Coolant for Hard Turning
For CBN tools above 50 HRC, use DRY only. Coolant causes thermal shock cracking. See our hard turning guide.
Browse mold-grade tooling in our end mill catalog.
