Mould and die manufacturing sits at the intersection of the highest material hardness, most complex three-dimensional geometries, and tightest surface finish requirements in all of metalworking. Machining H13 hot work steel at 50 HRC to produce a mirror-quality plastic injection mould cavity, or machining D2 cold work steel at 60 HRC for a precision blanking die — these operations demand the best tooling available, applied with the right strategy.
Vega Tools supports Indian and global mould and die manufacturers with solid carbide end mills, CBN tools, custom profile and injection bore cutters, and a full regrinding service to support the intensive tooling consumption of a mould shop.
The Mould Steel Family: Machining Properties
| Steel Grade | Type | Typical Hardness | Machining Challenge |
|---|---|---|---|
| P20 (1.2311) | Plastic mould steel | 28–34 HRC (pre-hardened) | Good machinability; can machine with standard carbide |
| H13 (1.2344) | Hot work die steel | 44–52 HRC | High hardness; requires AlTiN/nano-coat carbide |
| D2 (1.2379) | Cold work die steel | 58–62 HRC | Extreme hardness + abrasion; near CBN territory |
| S7 (1.2355) | Shock resistant die steel | 54–58 HRC | Tough + hard; requires corner radius end mills |
| 420SS Stainless | Corrosion resistant mould steel | 48–54 HRC | Gummy + hard; TiAlN, sharp geometry, flood coolant |
| Aluminium (7075, 6061) | Prototype / low-volume mould | 150–180 HB | Soft but abrasive; PCD or uncoated high-helix SC |
Hard Milling Strategy for Mould Cavities
Hard milling — direct machining of hardened steel without EDM — has become the primary cavity machining method in modern mould shops equipped with high-speed machining centres. The approach combines:
- High spindle speeds: 12,000–30,000 RPM for small-diameter ball nose end mills in cavity finishing
- Small radial depths (ae): 5–15% of cutter diameter — keeps cutting force low, reduces heat at the carbide edge
- Small axial depths (ap): 0.1–0.5 mm for finishing, 0.5–1.5 mm for semi-finishing
- High feed rates: Compensate for small depth with high feed — maintains productivity despite shallow cuts
- Dry or MQL machining: Thermal consistency is critical in hard milling — intermittent flood coolant causes temperature cycling that cracks carbide edge
Tool Recommendations for H13 at 48–52 HRC
| Operation | Tool | Coating | Speed (m/min) |
|---|---|---|---|
| Cavity roughing | SC ball nose, 2F, corner radius | AlTiN | 80–130 |
| Rib / wall semi-finish | SC ball nose 2F or 4F | AlTiN | 100–160 |
| Cavity floor semi-finish | SC corner radius 4F | AlTiN | 100–160 |
| 3D surface finish | SC ball nose 2F, sharp geometry | AlTiN nano | 130–200 |
| Flat face finish | SC 4F wiper geometry | AlTiN | 100–160 |
| Parting line / shut-off | SC 4F corner radius, short reach | AlTiN | 100–150 |
EDM Companion Tooling: Pre-Sinking and Post-EDM
In mould shops that use Electrical Discharge Machining (EDM/spark erosion) for complex features, carbide cutting tools play two important roles:
- Pre-EDM roughing: Milling with carbide removes the bulk of material before EDM — dramatically reducing EDM time (which is slow) and electrode wear. The closer the milled shape is to the final form, the faster and more economical the EDM finish.
- Post-EDM finishing: Some mould shops re-machine after EDM to remove the white layer (re-solidified steel) and bring the surface to Ra 0.4–0.8 μm using fine ball nose carbide end mills — avoiding the need for hand polishing on less-critical surfaces.
Precision Bore Machining in Moulds
Mould assemblies require many precision bores — guide pin bushings, ejector pin holes, sprue bores, hot runner nozzle seats, cooling circuit manifold bores. Each has specific tooling requirements:
Guide Pin Bushing Bores
Typically 16–50 mm diameter, H7 tolerance in P20 or H13 (pre-hardened). Solid carbide TC reamers from Vega Tools produce IT7 bores efficiently. For hardened H13 guide bores (48 HRC), solid carbide reamers in AlTiN coating achieve IT7 in production.
Ejector Pin Bores
Ejector pin bores require a very close clearance fit to the pin diameter (typically H7/f7 sliding fit). A slight oversize causes flash; slight undersize causes the pin to stick. Vega Tools solid carbide reamers produce consistent bores across a mould base — matched batch reaming ensures all bores in one mould are within 0.003 mm of each other.
Sprue Bushing and Hot Runner Bores
Sprue bushing bores combine a tapered entry with a cylindrical (or stepped) bore body. Custom injection bore cutters from Vega Tools machine the complete bore profile including taper, seat, and transition in two or three passes — eliminating the need to separately machine and then hand-blend the tapered entry with a ball nose end mill.
Cooling Circuit Drilling in Mould Bases
Mould cooling circuits are drilled with long-series carbide drills through P20 or H13 mould steel. Requirements:
- Drill straightness over long L/D (8–12× diameter for deep cooling channels)
- Through-coolant drills recommended for L/D above 5 to flush chips and prevent drill deflection
- TiAlN coated for tool life in P20; AlTiN for H13
Thread Milling in Hardened Mould Steel
Mould bases require lifting eye threads, clamping bolt threads, and hot runner heater support threads — often in hardened material (H13, 48 HRC) where HSS taps are unreliable. Solid carbide thread mills from Vega Tools are the correct choice for all threaded features in hardened mould steel. The single-form carbide thread mill runs comfortably in H13 at 48–52 HRC, producing clean threads without the catastrophic failure risk of a tap breaking in a finished, expensive mould base.