Gun Drilled Conformal Cooling Channels
Conformal cooling routes the cooling circuit to follow the cavity surface, cutting cycle time and eliminating hot spots. There are two ways to build it: additive manufacturing (3D-printed free-form lattices) and gun drilling — a chain of straight drilled segments connected at angles to approximate the conformal path. The gun-drilled route is cheaper for existing molds and steel inserts, works in any mold steel, and can be retrofitted to a tool already in service. This guide covers how drilled conformal works, how the channel ends are sealed, and what goes wrong.
For the design rules and ROI of conformal cooling, see deep hole drilling in mold and die making. This page focuses on the drilling-specific side.
How Gun Drilling Approximates a Conformal Path
A gun drill cuts straight holes — it cannot follow a curve. A conformal path is therefore built from straight segments drilled at angles, meeting at junctions, with the unused ends plugged:
[plug]-- seg 1 --\ seg 2 \-- seg 3 --[plug]
junction
Each segment is a gun-drilled through-hole Ø6–14 mm drilled from an accessible face of the mold or insert. Because the segments approach the cavity surface from different angles, the overall circuit tracks the contour far more closely than a straight grid — the reason drilled conformal typically cuts cycle time nearly as well as fully free-form channels at a fraction of the cost.
Drilled vs Additive Conformal
| Factor | Gun-drilled conformal | Additive (3D printed) conformal |
|---|---|---|
| Geometry | Straight segments + junctions | Free-form, fully conformal lattice |
| Mold steel | Any — drilled after hardening | Only printable alloys (often maraging, not H13) |
| Existing tools | Retrofit a mold already in service | New inserts only |
| Cost per channel | Lower, established process | Higher, build-chamber limits |
| Channel finish | As-drilled, smooth | Layer lines, often needs post-finishing |
| Corner capability | Limited at tight radii | Unlimited |
Choose gun drilling when the mold exists, the steel is a conventional tool steel, or cost matters. Choose additive when the geometry needs true free-form flow or the insert is being designed new from scratch.
Channel Routing and Plugging
The channel enters and exits the mold exterior. Where a straight segment does not need to exit, its end is plugged:
| Sealing method | How it works | Best for |
|---|---|---|
| Threaded plug | Tapped port, plug seals under pressure | Accessible ends, removable for cleaning |
| Tapered pin / press plug | Interference-fit pin | Blind ends away from the cavity |
| Welded plug | Seal-welded end, then ground flush | Permanent installation, cavity-side ends |
Place plugs clear of the cavity surface — the wall between a plug and the cavity must hold mold pressure, so follow the minimum-wall rule (typically 3 mm or more; see the mold and die design rules). Parallel segments are connected with cross-drills or baffles to complete the circuit.
Intersection Control
Where two drilled segments meet is the weakest point of a gun-drilled conformal circuit:
- Deburr every intersection. A drilling burr left at a junction becomes a flow disturbance, a stress raiser, and a trap for scale.
- Radius the junctions where the geometry allows — a sharp corner in the flow path adds pressure drop and turbulence.
- Keep wall thickness between intersecting channels above the minimum (typically 3 mm) so the junction does not collapse under pressure.
- Pressure-test the completed circuit after plugging, before the mold goes into service.
Materials and Parameters
Mold steels drill well by gun drilling when the parameters match the hardness: P20 around 80–110 m/min, H13 at 45 HRC down to 40–60 m/min, and 420 stainless around 50–70 m/min, at feeds near 0.020–0.040 mm/rev for a Ø10 mm channel. Full material parameters and drillability are in gun drilling on mold steels.
Common Failures
| Failure | Cause | Fix |
|---|---|---|
| Leaking plug | Plug too shallow, or wall too thin under pressure | Move plugs off the cavity; increase wall; re-seal |
| Wall collapse between channels | Channels drilled closer than minimum wall | Respect the 3 mm minimum; verify with ultrasonic |
| Blocked channel | Chips left inside after drilling | Blow out and flush every segment before plugging |
| Scale / corrosion in water lines | Open junctions trap deposits | Deburr and radius intersections; filter the water |
| Cracked junction | Sharp corner stress concentrator | Radius junctions; inspect after leak test |
FAQ
Can conformal cooling be gun drilled? Yes — as a chain of straight drilled segments connected at angles and sealed with plugs. It approximates a conformal path far better than straight grids, at lower cost than additive channels.
Gun drilling or 3D printed conformal cooling? Gun drilling for existing molds, conventional tool steels, and lower cost; additive for new inserts needing true free-form geometry. See the comparison table above.
How are blind channel ends sealed? With threaded plugs, tapered/press pins, or seal-welded ends, placed clear of the cavity surface so the wall holds mold pressure.
What diameter cooling channels? Typically Ø6–14 mm — the design-rule table in the mold and die guide gives the sizing logic by heat-transfer versus pressure-drop.
Summary
Gun-drilled conformal cooling approximates a cavity-following circuit with straight drilled segments, junctions, and plugs — giving most of the cycle-time benefit of free-form channels in any mold steel, retrofit-able to tools already in service. The drilling details that make or break it: deburr and radius every intersection, respect minimum walls, seal the plugs properly, and flush every segment before the mold runs. For the design rules and economics, see deep hole drilling in mold and die making.
For the drilling process fundamentals, see how gun drilling works. For hardened mold steel parameters, see deep hole drilling hardened steel.