Hitachi JPM Series: The Complete Guide to Mold Milling Carbide Inserts
Hitachi Metals (now operating as Proterial, Ltd. since 2023) has been a dominant force in mold and die milling inserts through its JPM series. Designed specifically for the demanding requirements of mold machining — where surface finish, dimensional accuracy, and long uninterrupted tool life are paramount — the JPM series has become the benchmark for high-precision copy milling and 3D contouring. This guide covers the complete JPM insert portfolio with grade specifications and application parameters.
Mold Milling Requirements
Mold and die machining presents unique challenges that differentiate it from production milling:
- Extended cutting times: A single mold cavity may require 8-40 hours of continuous milling without tool changes
- Complex 3D surfaces: Ball nose and radius cutters follow constantly changing engagement angles
- Hardened workpieces: Mold steels are typically machined at 30-62 HRC, often in the hardened state
- Surface finish demands: Ra 0.2-0.8 µm is often required directly from milling, eliminating or reducing polishing time
- Dimensional accuracy: Cavity tolerances of ±0.01-0.02 mm demand predictable, consistent tool wear
JPM Insert Families
| Series | Insert Shape | Corner Radii (mm) | IC Size | Primary Application |
|---|---|---|---|---|
| JPMW | Round (button) | R3-R12.7 | Ø6-Ø25.4mm | 3D contouring, copy milling |
| JPMT | Trigon | R0.4-R3.0 | 9.5-16mm | Shoulder milling, pockets |
| JPMF | Flat with wiper | R0.4-R1.6 | 9.5-16mm | Flat surface finishing |
| JPMB | Ball nose | R1-R10 | — | 3D profiling, engraving |
Hitachi/Proterial Grade Portfolio for Mold Milling
| Grade | Coating | Substrate | HRA | ISO Range | Application |
|---|---|---|---|---|---|
| ATH85N | AlTiSiN PVD (3µm) | Ultra-fine WC (0.4µm) | 93.0 | P10-P20 | Hardened steel finishing (50-62 HRC) |
| ATH65N | AlTiN PVD (2.5µm) | Fine WC (0.6µm) | 92.0 | P15-P30 | Hardened steel semi-finishing (40-55 HRC) |
| AC530U | TiAlSiN PVD (3µm) | Fine WC (0.8µm) | 91.5 | P20-P35 | Pre-hardened steel roughing (30-45 HRC) |
| AC520U | TiAlN PVD (2µm) | Fine WC (0.8µm) | 92.0 | P15-P30 | Pre-hardened steel finishing |
| AC720U | TiAlN PVD (2µm) | Medium WC (1.5µm) | 90.5 | P25-P40 | Soft steel roughing (20-30 HRC) |
| NS9530 | TiAlSiN PVD (3µm) | Ultra-fine WC (0.4µm) | 93.5 | P05-P15 | Hard milling, mirror finish (55-65 HRC) |
Grade Selection by Mold Steel Type
| Mold Steel | DIN/JIS | Hardness | Recommended Grade | Vc (m/min) | fz (mm/tooth) |
|---|---|---|---|---|---|
| P20 pre-hardened | 1.2311 / SCM440 | 30-34 HRC | AC530U, AC520U | 180-250 | 0.06-0.12 |
| H13 hot work | 1.2344 / SKD61 | 45-52 HRC | ATH65N | 120-180 | 0.05-0.10 |
| D2 cold work | 1.2379 / SKD11 | 55-60 HRC | ATH85N, NS9530 | 80-140 | 0.04-0.08 |
| Stavax stainless | 1.2083 / SUS420 | 50-54 HRC | ATH65N, ATH85N | 100-160 | 0.04-0.09 |
| NAK80 precipitation | — | 37-43 HRC | AC520U, AC530U | 150-220 | 0.06-0.12 |
| MAX5 hardened | 1.2767 | 58-62 HRC | NS9530 | 60-100 | 0.03-0.06 |
JPM Insert Geometry Options
| Geometry | Rake | Edge Prep | Best For | Surface Finish |
|---|---|---|---|---|
| -FR (Finishing Radius) | +10° | Honed 5µm | Semi-finishing, light roughing | Ra 0.6-1.2 µm |
| -FH (Finishing High) | +15° | Polished 2µm | Finishing, mirror surface | Ra 0.2-0.4 µm |
| -MR (Medium Radius) | +5° | Honed 10µm | General milling | Ra 1.0-2.0 µm |
| -MH (Medium Heavy) | 0° | Chamfer 20° | Roughing, scale removal | Ra 2.0-4.0 µm |
Hard Milling Parameters by Insert Size
| Insert | Grade | Workpiece (HRC) | Vc (m/min) | fz (mm/tooth) | ap (mm) | ae (mm) |
|---|---|---|---|---|---|---|
| JPMW Ø10 (R5) | ATH85N | 55-60 | 100-140 | 0.06-0.10 | 0.3-0.8 | 0.5-1.5 |
| JPMW Ø12.7 (R6.35) | ATH85N | 55-60 | 100-140 | 0.08-0.12 | 0.5-1.0 | 0.8-2.0 |
| JPMW Ø16 (R8) | ATH65N | 45-52 | 140-200 | 0.10-0.16 | 0.5-1.5 | 1.0-3.0 |
| JPMT 1135 (R1) | ATH85N | 55-60 | 80-120 | 0.04-0.08 | 0.3-0.8 | 0.3-1.0 |
| JPMT 1604 (R2) | ATH65N | 45-52 | 120-180 | 0.08-0.14 | 0.5-2.0 | 0.5-2.0 |
Competitor Mold Milling Systems
| Hitachi/Proterial | Mitsubishi | Kyocera | Sandvik | Iscar |
|---|---|---|---|---|
| JPMW Ø12.7 | SRM series | MEW series | CoroMill 210 | BALLPLUS |
| ATH85N | VP15TF | PR1525 | GC1015 | IC908 |
| ATH65N | VP20MF | PR1535 | GC1025 | IC907 |
| NS9530 | VP05RT | PR1515 | GC1005 | IC903 |
Surface Finish vs Cutting Speed Optimization
For mold finishing, there is a critical relationship between cutting speed, feed per tooth, and achievable surface finish:
| Target Ra (µm) | fz Max (mm/tooth, R5 insert) | Recommended Vc | Grade | Geometry |
|---|---|---|---|---|
| 0.2-0.4 (mirror) | 0.04-0.06 | 120-160 m/min | NS9530 | -FH polished |
| 0.4-0.8 (fine) | 0.06-0.10 | 100-150 m/min | ATH85N | -FH polished |
| 0.8-1.6 (semi-finish) | 0.08-0.14 | 120-180 m/min | ATH65N | -FR honed |
| 1.6-3.2 (roughing) | 0.12-0.20 | 150-220 m/min | AC530U | -MR honed |
Key Takeaways
- The JPM series is purpose-designed for mold and die machining — general-purpose milling inserts lack the precision and finish capability required
- NS9530 is the premium grade for hardened steel finishing above 55 HRC, achieving mirror surfaces of Ra 0.2 µm
- ATH85N is the workhorse grade for hardened steel (50-62 HRC), balancing wear resistance and toughness
- The -FH polished geometry is essential for finishing operations where Ra < 0.4 µm is required
- Always reduce feed per tooth before reducing cutting speed when targeting better surface finish
- JPMW round inserts provide the most versatile geometry for 3D contouring and copy milling
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