H13 hot-work tool steel is the dominant material for injection mould tooling worldwide — excellent hardness after heat treatment, good thermal fatigue resistance, and a long service life under repeated thermal cycling. When DMLS first emerged as a production tool, it was tool steel mould inserts with conformal cooling that provided the clearest commercial justification: cooling channels that follow the mould cavity surface cut injection moulding cycle times by 20–40% and eliminate hot spots that cause sink marks and warpage. At Layer X in Ahmedabad we produce H13 DMLS inserts for automotive, packaging, and consumer goods moulds.
Why Conventional Straight-Drilled Cooling Fails
Conventional mould cooling channels are drilled straight through the mould steel with a gun drill — limited to cylindrical channels that cannot follow the cavity geometry. The result: cooling is uniform in straight sections but poor in corners, ribs, and deep features where the mould surface is farthest from the nearest channel. Hot spots in these regions cause extended cycle times (waiting for the hot zone to cool) and part quality defects.
Conformal cooling channels — which DMLS uniquely enables — follow the mould cavity contour at a constant stand-off distance (typically 3–5 mm from the cavity surface). Thermal uniformity improves dramatically, and the cycle time reduction follows: cycle times of 45–60 seconds with straight drilling become 28–40 seconds with conformal cooling on the same part, a 20–40% reduction.
H13 Tool Steel DMLS Properties
| Property | H13 DMLS (as-printed) | H13 DMLS (hardened, 47–50 HRC) | Conventional H13 (hardened) |
|---|---|---|---|
| Hardness | 26–32 HRC | 47–52 HRC | 48–52 HRC |
| Tensile strength | 1,000–1,200 MPa | 1,600–1,900 MPa | 1,600–2,000 MPa |
| Thermal conductivity | 24 W/m·K | 24 W/m·K | 25–27 W/m·K |
| Tool life (injection shots) | — | 300,000–1,000,000+ shots | 500,000–2,000,000+ shots |
DMLS H13 after vacuum hardening achieves properties comparable to conventionally processed H13. The slight reduction in long-term tool life (vs conventional wrought+machined) is acceptable for the tooling economics enabled by conformal cooling.
Conformal Cooling Channel Design Rules
- Channel cross-section: Circular channels of 4–8 mm diameter are standard. Elliptical channels with the major axis parallel to the cavity surface improve cooling uniformity by 10–15% vs circular at the same stand-off distance.
- Stand-off distance: 3 mm minimum from cavity surface (wall thickness between channel and cavity). Less than 3 mm risks breakthrough when hardening causes minor thermal expansion.
- Channel-to-channel pitch: 1.5–2× channel diameter. Channels spaced more widely create non-uniform cooling; closer creates structural weakness in the inter-channel web.
- Inlet/outlet ports: Must be accessible from the mould's parting line or back face. Design these as straight sections terminating at the insert boundary for connection to the mould cooling manifold.
- Avoid sharp bends: Use radii of minimum 2× channel diameter. Sharp bends create turbulence-induced pressure drop and potential fatigue initiation sites.
Post-Processing Sequence for H13 Inserts
- Stress relief: 650°C × 2h (as-built residual stress is high in H13 — this step is mandatory)
- CNC rough machining of cavity and mounting surfaces (leave 0.3–0.5 mm stock)
- Vacuum hardening: 1,020–1,060°C × quench → 48–50 HRC target
- Double temper: 540–560°C × 2 × 2h (stabilises martensite)
- EDM or grinding of cavity to final drawing dimensions (±0.01 mm)
- Polishing of cavity surface to Ra <0.4 µm (SPI A-2 or A-3 finish)
- Pressure test cooling channels: 100 bar hydraulic, confirm no leakage
Economic Case for Conformal Cooling Inserts
A conformal-cooled H13 DMLS insert costs ₹80,000–2,50,000 (depending on size and complexity), compared to ₹40,000–1,50,000 for a conventional machined insert with straight-drilled cooling. The premium of ₹40,000–1,00,000 pays back through cycle time reduction: on a part with 10,000 annual shot volume and a 40-second straight-drilled cycle time, reducing to 28 seconds saves 33 machine-hours per year — worth ₹80,000–2,40,000 annually at typical IMM rates in India.
Layer X produces H13 DMLS inserts for toolmakers and OEMs across Gujarat and India. Contact us for conformal cooling design review and DMLS insert quotation.