Deep Hole Drilling in Mold & Die Manufacturing
Mold and die making is one of the largest applications of deep hole drilling outside of aerospace and automotive. Every injection mold requires cooling channels that regulate the temperature of the molded part, and every mold requires ejector pin holes that are straight, smooth, and precisely positioned.
This guide covers the four main mold & die applications — cooling channels, ejector pin holes, hot runner systems, and slide cores — with material-specific parameters for P20, H13, and S7 tool steels.
Key Applications and Parameters
1. Cooling Channels
Cooling channels (waterlines) are the most common deep hole drilling application in mold manufacturing. They carry temperature-controlled fluid to remove heat from the molded part, directly affecting cycle time and part quality.
Straight cooling channels are produced by gun drilling or BTA drilling in straight lines. They cannot follow complex 3D contours, so they must be positioned optimally relative to the cavity surface.
Design rules for straight cooling channels:
- Center-to-center spacing (pitch): ≤ 3× channel diameter
- Distance from channel to cavity surface: ≤ 1.5× diameter
- Minimum wall thickness between channels and cavity surface: 8 — 11% of channel diameter
| Parameter | Typical Value |
|---|---|
| Channel diameter | 6 — 16 mm |
| Depth | 100 — 1,000 mm |
| L/D ratio | 10:1 — 80:1 |
| Tolerance | IT8 — IT9 |
| Surface finish (as-drilled) | Ra 0.4 — 1.6 µm |
| Straightness | 0.05 — 0.3 mm/m |
| Mold steel | P20 (28 — 34 HRC), H13 (44 — 52 HRC) |
Production parameters (gun drilling, P20, 8 mm diameter, Guhring EB 100 M):
- Speed: 3,008 RPM
- Feed: 39 mm/min (0.013 mm/rev)
- Coolant: High-pressure oil, 50 — 200 bar
- Tool: Solid carbide single-flute gun drill, TiAlN-coated
Guhring documents this as a standard mold cooling channel application in material 1.2312 (similar to P20), drilling to 430 mm depth with a 7.94 mm EB 100 M monolithic gun drill. The process sequence: pilot hole (1.5 — 3×D deep with RT 100 XF drill) → pre-drill with RT 100 T at 323 mm/min → finish with EB 100 M at 39 mm/min (Guhring, 2024).
Conformal Cooling
Conformal cooling channels follow the contour of the mold cavity, providing uniform thermal control that straight channels cannot achieve.
| Comparison | Straight (Gun-Drilled) | Conformal (3D Printed) |
|---|---|---|
| Cavity surface ΔT | 5 — 7°C | 2 — 3°C |
| Cycle time reduction | Baseline | 10 — 40% |
| Warpage reduction | Baseline | Up to 90% |
| Channel cost per mold | Low — moderate | High |
| Maintenance | Standard | Prone to clogging (< 1 mm channels) |
Conformal cooling channels are typically produced by additive manufacturing (DMLS/LPBF), not deep hole drilling. However, hybrid approaches exist: the mold base is gun-drilled with straight channels, and conformal sections are added via inserts or DMLS. This combines the cost advantage of gun drilling with the thermal performance of conformal cooling.
2. Ejector Pin Holes
Ejector pins push the molded part off the core after ejection. The holes must be straight and smooth — any roughness causes pin sticking, part damage, or increased maintenance.
| Parameter | Value |
|---|---|
| Diameter | 2 — 12 mm |
| Depth | 50 — 400 mm |
| L/D ratio | 10:1 — 60:1 |
| Tolerance | IT7 — IT8 |
| Surface finish | Ra 0.4 — 0.8 µm |
| Straightness | ≤ 0.05 mm per 100 mm |
| Material | P20, H13, 4140 pre-hard |
Production approach: Gun drilling is preferred over conventional drilling for ejector pin holes because it produces a straight, burnished bore in a single pass. The burnishing action of the gun drill’s guide pads creates a surface finish that allows the ejector pin to slide freely without galling.
3. Hot Runner Systems
Hot runner manifolds and nozzles require precision deep holes for melt channels and heater cartridge bores.
| Parameter | Value |
|---|---|
| Melt channel diameter | 6 — 25 mm |
| Heater bore diameter | 6 — 18 mm |
| Depth | 50 — 400 mm |
| L/D ratio | 5:1 — 30:1 |
| Tolerance | IT7 — IT9 |
| Surface finish (melt channel) | Ra 0.4 — 0.8 µm |
| Material | H13, S7, stainless 420 |
Hot runner manifolds often require intersecting channels at precise angles, which demands gun drilling with angled entry. Mollart Machinery offers tooling solutions specifically for hot runner production, including multi-angle drilling capabilities (Mollart, 2024).
4. Slide Cores and Actuator Components
Slide cores and hydraulic actuators in complex molds require deep holes for coolant passages and hydraulic lines.
| Parameter | Value |
|---|---|
| Diameter | 4 — 20 mm |
| Depth | 100 — 500 mm |
| L/D ratio | 10:1 — 40:1 |
| Material | H13, S7, D2 |
Deep hole drilling for slide cores is typically done on 3+2 axis or 5-axis machines that can drill at compound angles to reach internal features without repositioning the workpiece.
Material-Specific Parameters
P20 (Pre-Hardened, 28 — 34 HRC)
P20 is the most common mold steel. It is relatively easy to gun drill.
| Diameter (mm) | Speed (m/min) | Feed (mm/rev) | Coolant Pressure (bar) |
|---|---|---|---|
| 6 — 8 | 70 — 90 | 0.010 — 0.025 | 50 — 100 |
| 8 — 12 | 60 — 80 | 0.015 — 0.035 | 40 — 80 |
| 12 — 16 | 50 — 70 | 0.020 — 0.050 | 30 — 60 |
H13 (Hardened, 44 — 52 HRC)
H13 requires reduced speeds and higher coolant pressure due to its hardness and low thermal conductivity.
| Diameter (mm) | Speed (m/min) | Feed (mm/rev) | Coolant Pressure (bar) |
|---|---|---|---|
| 6 — 8 | 40 — 60 | 0.008 — 0.015 | 80 — 150 |
| 8 — 12 | 35 — 50 | 0.010 — 0.020 | 60 — 120 |
| 12 — 16 | 30 — 45 | 0.015 — 0.030 | 50 — 100 |
S7 (Hardened, 54 — 56 HRC)
S7 is the most difficult to drill among common mold steels. Use carbide tooling with AlTiN or AlCrN coating and conservative parameters.
| Diameter (mm) | Speed (m/min) | Feed (mm/rev) | Coolant Pressure (bar) |
|---|---|---|---|
| 6 — 8 | 20 — 35 | 0.005 — 0.012 | 100 — 200 |
| 8 — 12 | 18 — 30 | 0.008 — 0.015 | 80 — 150 |
Machine Considerations for Mold & Die
Milling + Drilling Combination Machines
UNISIG’s USC-M series combines milling and deep hole drilling in a single machine, allowing mold shops to drill cooling channels and then mill cavity details without moving the workpiece.
MSI Mold Builders case study: A UNISIG USC-3M hybrid machine (3+2 axis with universal spindle) diverted 50% of gundrill traffic from dedicated machines, reduced total machining time per tool by 10 — 15%, and increased mold output by 5%. Gundrilling depth reached 71 inches (180 cm) per side with angle drilling range of +30° to -15°. A single setup replaced six previous setups between a horizontal boring mill and a separate gundrill (UNISIG / Engineering.com, 2024).
Key Machine Features for Mold Work
| Feature | Benefit |
|---|---|
| 5-axis or 3+2 capability | Drill angled cooling channels without repositioning |
| High-pressure coolant (100+ bar) | Required for H13 and S7 at high L/D ratios |
| Whip guides | Support long drills for deep cooling channels |
| BTA capability | Faster material removal for large-diameter channels |
| Large table capacity | MSI’s USC-M handles up to 66,150 lbs (30,005 kg) |
Starting Points Summary
Mold cooling channel, P20 steel, 8 mm diameter, 400 mm deep (50:1 L/D):
- Method: Gun drilling with pilot hole
- Speed: 75 m/min (≈ 2,980 RPM)
- Feed: 0.015 mm/rev
- Coolant: 80 bar, oil-based
- Tool: TiAlN-coated carbide single-flute gun drill
- Process sequence: Pilot (1.5 — 3×D) → Gun drill to depth
- Expected finish: Ra 0.8 — 1.6 µm, IT8 — IT9
Ejector pin hole, H13 steel, 4 mm diameter, 200 mm deep (50:1 L/D):
- Method: Gun drilling
- Speed: 50 m/min (≈ 3,980 RPM)
- Feed: 0.010 mm/rev
- Coolant: 100 bar
- Expected finish: Ra 0.4 — 0.8 µm, IT7 — IT8
References
- Guhring. Deep Hole Drilling in Mould Making — EB 100 M Application Example. Technical Documentation, 2024.
- Guhring. Tools for the Mould and Die Industry. Product Catalog, 2024.
- UNISIG. Solutions for Mold Manufacturers — USC-M Hybrid Machines. Technical Brochure, 2024.
- UNISIG / Engineering.com. UNISIG Redefines Mold Making — Hybrid Milling/Drilling. 2024.
- UNISIG / CTE Magazine. Moldmaking Multitasking — MSI Case Study. Cutting Tool Engineering, 2024.
- UNISIG. Hybrid Milling/Drilling Machine Reduces Total Mold Machining Time. 2024.
- Mollart Machinery. Innovative Tooling Solution for Hot Runner Production. 2024.
- Hole Specialists Inc. Mold Manufacturing Precision Machining — Cooling System Solutions. 2024.
- HPMT Industries. How to Achieve Precise Deep Hole Drilling with Long Drills. 2024.
- 6-Axis Deep-Hole Drilling & Milling in Mold Making — HOWMIN Machinery. 2024.
- Smart Lathe. How to Select Appropriate Machining Parameters for Deep Hole Drilling. 2024.
- Harsmarg Industries. How Does Small Hole Drilling Benefit Modern Mold Production? 2024.
- GoodTech MFG. Conformal Cooling vs. Standard Cooling — ROI Analysis. 2024.
- Bozilla Corp. A Deeper Understanding of Conformal Cooling for Injection Molds. 2024.
- Patent US7134813. Cooling Channel Geometry for Deep Hole Drilling Tools. 2006.