Dongying (Suzhou Dongying Electronic Technology Co., Ltd.) is a mold maker and injection molder in Suzhou, China. We build molds and molded parts for automotive components and electronics cooling, including fan impellers, fan frames and bases.
Why fan impeller injection molding is hard to keep consistent
Short answer: thin blades, a thick hub and a spinning part leave little room for uneven filling or cooling.
An impeller looks simple. It has a hub, a ring of blades and sometimes a shroud. In practice, it is one of the less forgiving parts in a cooling module. Three features combine:
- Thin blades next to a thicker hub. Thin sections freeze fast. The hub keeps shrinking. Stress and distortion start at the transition.
- Symmetry the process must keep. Every blade should fill, pack and cool the same way. If one side of the mold runs warmer, blade pitch and blade plane drift.
- A balance requirement. Residual unbalance belongs to the finished rotor. It depends on the impeller, the shaft or hub insert, and the assembly.
So a good thin-wall impeller mold starts with a review that looks at geometry, material and process together.
Materials for injection molded fan impellers: PBT, PA66-GF and LCP
Short answer: pick the material from the fan's temperature, speed and stiffness needs, then check how it molds.
| Material | Typical use | Watch for |
|---|---|---|
| PP / ABS | General ventilation, moderate loads and temperatures | Lower stiffness and heat resistance |
| PBT (often glass-filled) | Higher stiffness and heat resistance | Directional shrinkage when glass-filled |
| PA66 with glass fiber | Stiff, heat-resistant blades | Directional shrinkage; moisture changes size |
| LCP | Very thin, stiff blades | Needs uniform walls, balanced runners, good venting |
Glass fibers add stiffness. They also align with the flow. The material then shrinks less along the flow than across it. Distributor guidance on glass-filled PBT names this as the main cause of warpage (Sales Plastics, 2026).
An LCP impeller suits very thin blades because the melt flows easily into thin sections. Celanese's Vectra guidance stresses uniform walls, balanced runners and good venting (Celanese). Some fan brands market LCP impellers for stiffness (Noctua).
The final grade should come from the fan's design and test plan. A mold maker can comment on moldability.
Gate design for impeller injection molding: keep every blade equal
Short answer: gate at the hub, symmetrically, so melt reaches each blade at the same time and pressure.
A central gate on the hub lets melt travel outward evenly. Disk, diaphragm and symmetric multi-point gates all work this way. A side gate creates a long path and a short path. That often shows up as uneven blades.
Gate count also changes fiber orientation. A Moldflow study on glass-filled PA66 found that going from one gate to three cut the warpage from corner effects, because fiber orientation became more even (ICIMM 2015).
For impellers, simulate the fill with the actual grade. Check where weld lines fall, since a weld line at a blade root is a weak point. Compare gate options before the design is frozen.
Cooling and packing: control distortion at the hub
Short answer: cool both mold halves evenly and pack the hub without over-packing the blades.
Even fill does not help if cooling is uneven. Points that come up in review:
- Cooling circuits in core and cavity, each with its own control.
- Extra cooling near the hub, where the material is thickest.
- Enough packing to offset hub shrinkage. Delrin's gear guidance makes the same point: gate into the thickest section, with a gate that does not freeze early (Delrin).
- Vents at blade tips and flow ends to avoid burns and short shots.
Mold-flow analysis guides these choices. Mold trials confirm them. The agreed checks, not the simulation, decide acceptance.
Impeller balance: agree the criterion before tooling
Short answer: write down the balance grade, test speed and test assembly before the mold is designed.
ISO 21940-11 sets out how to define allowable residual unbalance for rigid rotors. It uses balance quality grades (G-grades) tied to rotor mass and maximum speed (ISO). The right grade for a given fan is the customer's decision.
Settle these points early:
- The balance grade or allowed residual unbalance, and its speed.
- Whether you measure the bare impeller or the impeller with its hub or rotor.
- The fixture, the correction method and the sampling plan.
- Related checks: outside diameter, blade pitch, blade plane, hub bore and runout.
Once these are written down, the mold design can target the features that drive balance. Trial results also become comparable.
Fan frame molds, bases and server fan housings
Short answer: review the fan frame mold and the impeller mold together, because tip clearance links them.
Frames and bases carry the motor, set tip clearance and mount into the system. Flatness, hole positions and the gap to the blade tips matter as much as the impeller. A shared tolerance plan for frame and impeller reduces assembly surprises.
For server and AI-hardware fans, buyers also ask about plastic parts in liquid cooling. Analysts expect liquid cooling to reach most AI-chip deployments in 2026 (TrendForce, 2026). Injection-molded polymer quick disconnects that follow Open Compute Project specifications are now on the market (Autotech Review, 2026; OCP UQD v2.0.0). Dongying can evaluate plastic parts for liquid-cooling assemblies against your drawings and specifications.
RFQ checklist for cooling fan impeller injection molding
Short answer: send drawings, material, speed, balance method and quantities. List any open items as questions.
| Input | What to include |
|---|---|
| Drawings | 2D drawing and 3D model with revisions; which one controls each dimension |
| Material | Grade, or the requirements if the grade is open |
| Operation | Maximum and continuous speed, rotation direction, temperature range |
| Balance | Criterion, test method, and the assembly it applies to |
| Critical dimensions | Blade pitch, blade plane, hub bore, outside diameter, tip clearance |
| Appearance | Cosmetic needs, gate and ejector limits |
| Quantities | Samples, annual demand and target schedule, listed separately |
| Delivery model | Mold handed over to your plant, or parts molded by Dongying |
Missing items are fine. It is better to review them as open questions than to fill them with guesses. Send your inquiry.
FAQ
How are thin-wall fan impellers injection molded?
They are usually molded with a central or symmetric hub gate, so melt reaches every blade evenly. Both mold halves are cooled, with extra attention to the thicker hub. Mold-flow simulation with the actual material is used to compare gate options and predict weld lines and distortion. The agreed dimensional and balance checks are then confirmed on trial samples before release.
Which materials are common for fan impellers?
General ventilation fans often use PP or ABS. PBT and glass-fiber PA66 are chosen when more stiffness and heat resistance are needed, though glass fibers make shrinkage directional. LCP is used for very thin, stiff blades because it flows easily into thin sections. The final grade should follow the fan's operating temperature, speed and test requirements.
How is impeller balance considered in mold design?
Balance is addressed by keeping fill, packing and cooling the same for every blade. That means symmetric gating, balanced cooling and smooth wall transitions. The balance criterion, often an ISO 21940-11 grade or a residual unbalance value, should be agreed before tooling. The test speed, fixture and the assembly being measured should be agreed at the same time.
Can you mold fan frames and bases as well as impellers?
Yes. Dongying makes molds and molded parts for fan impellers, frames and bases. Reviewing frame and impeller together helps align tip clearance, mounting features and flatness requirements. Send the drawings for each part and the assembly relationship, and we will review moldability and the inspection points with you.
What do you need to quote a fan impeller mold?
Please send the 2D drawing and 3D model with revisions, the material requirement, speed and temperature range, balance criterion and test method, and critical dimensions. Add cosmetic needs, sample and annual quantities, and whether you want the mold delivered to your plant or molded parts. You can also inquire without a drawing.
Do you support plastic parts for liquid-cooling assemblies?
We can evaluate plastic parts for liquid-cooling assemblies, such as housings or fluid-path components. The review is based on your drawings, material specification and validation requirements. Coolant compatibility, pressure and leak testing are defined by your system specification, so we review those requirements with you before any tooling decision.
Related pages
Sources
- Sales Plastics, "Preventing Warpage in 30% GF PBT Injection Molding," May 14, 2026. https://salesplastics.com/pbt-injection-molding-preventing-warpage-30-gf/
- Celanese, "Tech Tips: Vectra LCP" (precision molding guide). https://www.celanese.com/-/media/Engineered%20Materials/Files/Product%20Technical%20Guides/LCP-001_VectraLCPprecMoldTG_AM_0613.pdf
- "Optimization of Injection Process Parameters to Reduce Warpage in Glass Fiber-Reinforced Polyamide Molded Parts," ICIMM 2015, Atlantis Press. https://doi.org/10.2991/icimm-15.2015.121
- Delrin, "Mold Delrin gears with precision." https://www.delrin.com/mold-delrin-gears-with-precision/
- ISO 21940-11:2016 (+Amd 1:2022), Rotor balancing – rigid rotors. https://www.iso.org/standard/54074.html
- TrendForce, "Liquid Cooling Becomes Standard for High-End AI Infrastructure…," Aug 17, 2026. https://www.trendforce.com/presscenter/news/20260817-13183.html
- Autotech Review, "ARaymond Introduces Next-Generation UQDs for Data Center Liquid Cooling," Oct 1, 2026. https://autotechreviews.com/index.php/technology/item/1299-araymond-introduces-next-generation-uqds-for-data-center-liquid-cooling
- Open Compute Project, UQD/UQDB Design Specification v2.0.0 (effective Sep 22, 2026). https://www.opencompute.org/documents/ocp-design-spec-uqd-v2-0-0-pdf/
- Noctua, "Sterrox LCP." https://www.noctua.at/en/expertise/tech/sterroxr-liquid-crystal-polymer-lcp