Deep Hole Drilling in Mold and Die Making
Gun drilling is extensively used in mold and die making for cooling channels, ejector pin holes, and heater passages. Conformal cooling — channels that follow the contour of the mold cavity — is one of the most value-added applications of deep hole drilling in any industry.
This guide covers mold and die applications, channel design strategies, and the return on investment for gun-drilled conformal cooling.
Key Mold and Die Applications
Conformal Cooling Channels
Conformal cooling is the most impactful application of deep hole drilling in mold making. Channels drilled close to the cavity surface provide efficient, uniform cooling that reduces cycle time and improves part quality.
| Channel Feature | Typical Spec | Method |
|---|---|---|
| Diameter | Ø6–16 mm | Gun drilling |
| Depth | 100–1,000 mm | Gun drilling |
| Distance from cavity surface | 8–15 mm (optimal) | Design-dependent |
| Spacing between channels | 2–3× channel diameter | Thermal analysis |
| Material | P20, H13, 420 stainless | Gun drilling |
Benefits of gun-drilled conformal cooling:
- 20–40% reduction in cycle time
- 50–80% reduction in scrap
- Improved part quality (less warpage, more uniform shrinkage)
- Extended mold life (reduced thermal stress)
Ejector Pin Holes
Ejector pin holes require straight, precise bores with good surface finish for smooth pin movement.
| Feature | Spec |
|---|---|
| Diameter | Ø3–20 mm |
| Depth | 50–300 mm |
| Tolerance | H7 (ISO fit for sliding pins) |
| Surface finish | Ra 0.4–0.8 µm |
| Method | Gun drilling (often from both ends) |
Heater and Sensor Passages
| Application | Typical Bore | Method |
|---|---|---|
| Cartridge heater holes | Ø8–20 mm × 50–500 mm | Gun drilling |
| Thermocouple holes | Ø3–6 mm × 50–300 mm | Gun drilling |
| Hot runner manifold passages | Ø6–12 mm × 100–600 mm | Gun drilling |
Channel Design Strategies
Conventional (Straight) Cooling
Straight-drilled cooling channels cannot follow complex cavity geometries. They are limited to:
- Straight holes from the outside of the mold
- Simple grid patterns
- Limited coverage of the cavity surface
Conformal Cooling (Gun-Drilled)
Gun drilling enables curved or angled channels that:
- Follow the cavity contour
- Stay close to the cavity surface (8–15 mm versus 15–25 mm for straight drilling)
- Provide uniform cooling across the entire cavity
- Eliminate hot spots
Cooling Channel Layout
┌─────────────────────────┐
│ Mold cavity │
│ ┌─────────┐ │
│ │ │ │
Gun-drilled ←───┼────┤ ├──────────┼───→
channels │ │ │ │
following │ └─────────┘ │
cavity contour │ │
│ ←── Baffles ──→ │
└─────────────────────────┘
Design Rules
| Rule | Recommendation | Why |
|---|---|---|
| Channel diameter | Ø8–14 mm | Optimal for heat transfer vs. pressure drop |
| Distance from cavity | 2–3× channel diameter | Close enough for heat transfer, far enough for strength |
| Channel spacing | 3–5× channel diameter | Prevents thermal interference |
| Minimum wall between channels | 3 mm | Structural integrity |
| Entry and exit | Both ends accessible for gun drilling | Required for through-holes |
| Cross-hole intersection | Avoid intersecting channels closer than 3 mm | Wall collapse risk |
ROI of Conformal Cooling
Cost Savings Calculation
For a typical injection mold:
| Factor | Conventional Cooling | Conformal Cooling (Gun-Drilled) |
|---|---|---|
| Cycle time | 45 seconds | 30 seconds (−33%) |
| Scrap rate | 5% | 1% (−80%) |
| Mold cost (additional for conformal) | Baseline | +$5,000–15,000 |
| Annual production | 100,000 parts | 100,000 parts |
| Annual savings from cycle time | — | $20,000–50,000 |
| Annual savings from scrap | — | $3,000–8,000 |
| Payback period | — | 3–6 months |
When Conformal Cooling Pays
| Production Volume | Payback Period |
|---|---|
| < 10,000 parts/year | > 2 years (not recommended) |
| 10,000–50,000 parts/year | 6–18 months |
| 50,000–200,000 parts/year | 2–6 months |
| > 200,000 parts/year | Under 2 months |
Materials
| Mold Steel | Drillability | Typical Application |
|---|---|---|
| P20 (30–35 HRC) | Excellent | Standard injection molds |
| H13 (45–52 HRC) | Good | Die casting, high-temperature molds |
| 420 stainless (30–35 HRC) | Good | Corrosion-resistant molds (PVC) |
| S7 (45–50 HRC) | Moderate | Shock-resistant applications |
| NAK80 (38–42 HRC) | Good | High-polish molds |
Gun Drilling on Mold Steels
| Parameter | P20 | H13 (45 HRC) | 420 Stainless |
|---|---|---|---|
| Speed (m/min) | 80–110 | 40–60 | 50–70 |
| Feed (mm/rev, Ø10 mm) | 0.020–0.040 | 0.012–0.025 | 0.015–0.030 |
| Coolant pressure | 35–70 bar | 50–100 bar | 50–80 bar |
| Tool coating | TiAlN | AlTiN | TiAlN |
Summary
Deep hole drilling in mold and die making — particularly gun-drilled conformal cooling channels — offers one of the highest returns on investment in the industry. The 20–40% reduction in cycle time typically pays back the cost of gun drilling within 3–6 months on production molds. Beyond cooling, ejector pin holes and heater passages are standard gun drilling applications that benefit from the process’s precision and straightness. Mold steels (P20, H13, 420 stainless) drill well with standard carbide tooling and appropriate coatings.
For method-specific parameters, see gun drilling parameters. For material-specific drilling, see materials drilling guide. For a complete overview, visit the industry applications guide.
For the drilling-specific side of conformal cooling — segment routing, plugging, intersections, and failures — see gun drilled conformal cooling channels.