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Thermal Physics and Turbulent Coolant Flow
Cooling is usually the longest step in an injection molding cycle. The part cannot be ejected until its hottest spot drops below the ejection temperature, so the slowest cooling area sets the cycle for the whole mold. With gun drilled lines and baffles, that area is almost always somewhere the drill cannot reach: a deep core, a tall rib, a thread root or a sharp inside corner. Conformal channels wrap around those areas at a steady distance from the molding surface, so the whole part cools at a similar rate.
Keeping the Water Turbulent
Heat moves from the steel into the water much faster when the flow is turbulent. As a rule of thumb, designers aim for a Reynolds number above 4,000, and many target 10,000 or higher. Below that the flow turns laminar and a slow layer of water clings to the channel wall and insulates it. Conformal circuits are longer and narrower than drilled lines, so TK sizes the channel diameter and flow rate with a Moldflow cooling analysis and checks the pressure drop, the flow and the water temperature rise from inlet to outlet before the insert is printed.
Conformal cooling is designed into the whole tool, not added at the end. See how it fits into our custom injection mold tooling and our DFM and Moldflow review.
Conformal vs Conventional Drilled Cooling
| Characteristic | Conventional drilled lines | Conformal cooling | What it means in production |
|---|---|---|---|
| Channel path | Straight lines, plugs, baffles and bubblers | Curved channels that follow the part shape | Water reaches cores, ribs and thread roots |
| Distance to the molding surface | Changes around corners and deep features | Held even, typically about 1.5 to 2 times the channel diameter | Even cooling, less differential shrink |
| Hot spots | Corners, deep cores and thread roots run hot | Cooling follows the hot areas | Less warpage, sink and internal stress |
| Cycle time | Set by the slowest cooling area | Up to 35% shorter on TK molds | More parts per hour from the same press |
| How it is made | Drilled in solid steel | Printed in maraging steel, or diffusion bonded | Higher insert cost, paid back in cycle time |
Channel offset is a typical design rule; the actual layout is set for each insert with a Moldflow cooling analysis.
3D Metal Sintering Metallurgy: 1.2709 Maraging Steel
TK prints conformal cooling inserts in house on a 3D Systems DMP Flex 350 direct metal printer, which builds the insert one thin layer of laser melted steel powder at a time, with the cooling channels formed inside it. TK has run its own 3D printing since 2018.
Finishing and Hybrid Inserts
After printing, the insert is age hardened and its shutoffs, fits and molding surfaces are machined and polished like any other insert, down to an SPI A2 finish where the part needs it. Printing only the section that needs conformal cooling, a hybrid approach, keeps the insert cost down.
Diffusion Bonding
TK also builds conformal channels by diffusion bonding. The channels are machined into separate layers of steel, and the layers are bonded under heat and pressure into one solid block, so the channel path is not limited to straight drilled lines.
Conformal Cooled Molds Built by TK
TK uses conformal cooling where one insert holds the cycle back, usually a deep or thin core. Data is from TK’s project records.
| Part | Cavities | Resin, Weight | Press | Cycle | Where conformal cooling went |
|---|---|---|---|---|---|
| 2K pull ring flip top cap, ø34 x 27 mm | 12+12 | PP + TPE, 6.75 g | 420 T | 21 s to 17 s | Critical insert; mold shipped 10 weeks after the PO |
| Actuator cap, ø35 x 21 mm | 16 | PP | 400 T | 13 s | Core insert; 4 orifice version |
Checked at Trial
Every mold is qualified in TK’s testing center with cooling circuit testing, mold temperature testing and pressure loss analysis, along with the dry cycle and short shot balance. For more on how molds are proven out, see our mold trials and quality verification page.
Interactive Conformal Cooling Savings Calculator
Enter your current cycle, how much of it is cooling, and how much conformal cooling should cut the cooling time. The calculator works out the new cycle, parts per hour and the press hours your annual volume needs before and after. Add your press hour rate and your quote for the conformal inserts to see the payback. Open “Show the math” to see every step.
Show the math
The default numbers match TK’s 12+12 two shot cap mold, which went from 21 s to 17 s with conformal cooling on the critical insert. Your result depends on the part, the resin and where the hot spot is; TK checks it with a Moldflow cooling analysis before quoting. No prices are built in; the payback uses only the numbers you enter.
Technical Sourcing FAQ: Conformal Cooling
Want to Eliminate Cycle Delays with Conformal Cooling?
Send your part CAD, resin and current cycle to Brandon Henderson, Technical Sales Support Manager for the Americas. TK’s engineers will run a Moldflow cooling analysis and show where conformal cooling pays off.