The cavity is not the only important shape inside an injection mold. Coolant channels can determine how soon a part may be ejected and whether it keeps its dimensions.
Straight drilled channels are practical for simple parts. Around a deep or curved molding surface, their distance from the plastic varies. Heat travels farther through the metal in some areas, leaving hot zones. A conformal channel follows the part contour inside a replaceable insert, making those heat paths more even. Flowing coolant then carries the heat away.
What one experiment compared
A 2025 UNED study tested Metal-FFF inserts in an injection molding machine.[1] Metal-filled filament was printed, debound, and sintered. The researchers used polypropylene copolymer and applied the same injection settings to conventional and conformal insert sets.
Both used 17-4 PH stainless steel, but the conventional replicas were machined and the conformal inserts were printed. The exterior conventional insert could not contain an internal channel and relied on water circulating in the mold base. The result therefore compares two complete mold configurations, not channel geometry alone.
At the acceptable quality limit, the total cycle was 65.7 seconds for conventional cooling and 40.7 seconds for conformal cooling, a reported 38% reduction. At a 20-second cooling time, the conventional part showed clear ovality while the conformally cooled part retained dimensional accuracy.
The team produced 950 units in an eight-hour run without observing cracking, deformation, underfilling, or coolant leakage. That is preliminary evidence, not a production-life guarantee. The authors note that conventional molds may run for hundreds of thousands of cycles while Metal-FFF fatigue remains insufficiently characterized. Sintering shrinkage and porosity also need control.
Faster cooling still has a floor
A separate 2020 study used a laser-melted maraging-steel insert for a thermoplastic pressure-fitting cap.[2] It reduced the cycle from 47 to 32 seconds while keeping the part within ±0.2 mm. Shorter cycles caused sink marks and warping. Success meant an earlier ejection point that still met the part's functional requirements.
In the 2022 computational case, serpentine channels had significantly higher pressure drops than circular-section reference channels and were less preferred.[3] The study optimized cooling time, surface-temperature non-uniformity, and pressure drop together. X-ray CT separately checked the printed geometry.
A practical decision rule
Record the current mold's hot zones, cooling time, and the defect that appears after earlier ejection. Compare the same part under steady production for temperature variation, dimensions, warpage, sink marks, required coolant flow and pressure, leakage, cleaning, repair, and target tool life.
If straight drilling already cools the part uniformly enough, a printed insert may add cost without removing a constraint. If unreachable curves repeatedly cause hot spots, delay, and defects, and those losses exceed the cost of making and validating an insert, conformal cooling becomes a concrete candidate.
Sources:
- https://oai.e-spacio.uned.es/server/api/core/bitstreams/a170be79-ff29-41f4-a3e3-695f4a10175d/content
- https://mdpi-res.com/d_attachment/jmmp/jmmp-04-00100/article_deploy/jmmp-04-00100.pdf
- https://mdpi-res.com/d_attachment/polymers/polymers-14-00424/article_deploy/polymers-14-00424.pdf
- https://www.eos.info/industries/customer-success-stories/automotive-transportation/innomia-automotive-3d-printed-cooling-channels
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