AFPM Core Air Gap Design
Estimate the first-pass AFPM core air-gap flux density, then use the evidence tables to decide whether the concept is ready for nonlinear FEA, supplier RFQ, or tolerance redesign.
What To Do With The Result
The tool answers the immediate sizing question. The report layer explains when the answer is useful, when it is unsafe, and what evidence a supplier or internal design team should produce next.
Key Design Conclusions
Method And Evidence
The estimator uses a simple magnetic-circuit relationship for a magnet and an air gap:
Worked Calculator Examples
Evidence Ledger
| ID | Source | How it is used | Date marker |
|---|---|---|---|
| S1 | Arnold Magnetic Technologies - NdFeB magnet overview | Sanity-checks magnet remanence and grade/temperature dependency used by the Br input. | July 23, 2026 |
| S2 | JMAG International and Hoganas - SMC in motor design | Supports the need to evaluate SMC with material curves and motor-design simulation rather than a steel-core assumption. | July 23, 2026 |
| S3 | Sumitomo Electric - soft magnetic composite overview | Supports SMC manufacturability and high-frequency magnetic-core positioning for compact motor components. | July 23, 2026 |
| S4 | Axialfluxcore - SMC vs laminated axial flux core guide | Internal sourcing and DFM framing for AFPM stator/core material selection, reviewed as site context. | July 20, 2026 |
| S5 | Axialfluxcore - magnetic loss testing in high-frequency AFPM | Internal validation workflow for B-H curves, W/kg loss data, density reporting, and frequency-specific qualification. | July 20, 2026 |
Design Bands And Actions
| Screening condition | Interpretation | Next action |
|---|---|---|
| Bg below 0.40 T | Low magnetic loading | Check whether the design intentionally trades torque density for clearance, cost, or a low-risk first prototype. |
| Bg from 0.40 T to 0.90 T | Practical first-pass screening band | Proceed to leakage, slotting, saturation, tolerance, and thermal-growth checks before freezing geometry. |
| Bg above 0.90 T | High magnetic loading | Require nonlinear 3D FEA, local tooth-flux review, magnet irreversible-loss margin, and housing stiffness proof. |
| Mechanical gap below 0.80 mm | Boundary manufacturing case | Do not release tooling without runout, bearing growth, adhesive stack, debris, and rotor deflection evidence. |
Material Route Trade-Offs
Air-gap design depends on the chosen core route. SMC and laminated steel can both be valid, but they need different proof.
| Dimension | SMC route | Laminated route | Decision use |
|---|---|---|---|
| Flux path fit | Strong fit for 3D flux paths and segmented AFPM geometries. | Strong in 2D flux paths; axial layouts often need winding, stacking, or machining compromises. | Use SMC when geometry benefits from 3D flux and high-frequency operation. |
| Magnetic model risk | Requires supplier B-H and loss curves because permeability and density depend on compaction route. | Higher permeability is familiar, but cut-edge stress and stacking quality still need validation. | Never carry steel-core assumptions into an SMC air-gap model. |
| Mechanical risk | Brittle core material; housing and carrier should absorb axial load. | Mechanically robust, but stack bonding and machining quality affect air-gap faces. | Place stiffness requirements on the assembly, not only the core material. |
| RFQ evidence | Ask for density map, B-H curve, W/kg loss data, pressing direction, ejection feasibility, and face grinding plan. | Ask for lamination thickness, coating, stack factor, cut-edge process, bonding method, and flatness. | Compare both routes with measurable evidence, not generic material labels. |
Tolerance Stack To Verify
| Input | Why it matters | Verification method |
|---|---|---|
| Mechanical air gap | Sets the visible rotor-to-core clearance, but only one part of magnetic reluctance. | CMM or optical scan on assembled stack at room temperature. |
| Bondline and coating thickness | Non-magnetic layers add effective gap and can vary around the rotor face. | Supplier coating spec, adhesive process window, and sectioned sample audit. |
| Rotor and housing axial stiffness | Magnetic attraction can close the gap under load even if static inspection passes. | FEA deflection case plus dial-indicator or laser displacement test. |
| Thermal growth | Magnets, carrier, shaft, housing, and core can move differently across duty cycles. | Hot-state stack model and thermal soak inspection. |
| Runout and bearing play | Uneven local gap drives torque ripple and rub risk. | Rotating runout measurement at assembly and after endurance cycling. |
Risks And Controls
| Risk | Impact | Likelihood | Mitigation |
|---|---|---|---|
| Misusing the 1D calculator as final design proof | High | Medium | Use the calculator only for concept bands, then require 3D FEA with source-specific material data. |
| Sub-0.8 mm gap without stiffness evidence | High | Medium | Add axial deflection, thermal growth, runout, and debris-clearance gates before prototype release. |
| SMC B-H curve assumed from generic data | High | Medium | Request batch-specific B-H and W/kg loss curves from the selected powder and compaction process. |
| Thick magnet selected to compensate for a wide gap | Medium | Medium | Compare cost, rotor inertia, demagnetization margin, and assembly force before approving magnet thickness. |
| RFQ only specifies nominal gap | Medium | High | Specify effective magnetic gap stack, measurement method, hot-state limits, and acceptance evidence. |
Scenario Examples
Buyer Checklist
Magnet grade, Br at operating temperature, recoil permeability, coating thickness, and irreversible-loss curve.
Core material route, supplier B-H curve, W/kg loss curve, density map, and compaction or lamination process note.
Mechanical gap, effective magnetic gap, adhesive stack, sleeve stack, runout, bearing play, and thermal growth budget.
3D FEA case list covering nominal, worst-case tolerance, hot-state, and demagnetization-margin conditions.
Inspection method, sample size, pass-fail threshold, and corrective action when measured gap is out of band.
FAQ
Ready to validate an AFPM core air-gap stack?
Send the calculator band, CAD stack, material route, duty cycle, and target production volume. We will review whether the design needs magnetic, mechanical, or sourcing changes before prototype tooling.