AFPM Core Design for Manufacturing
AFPM core design for manufacturing starts with the pressing route, projected area and drawing requirements. Estimate SMC pressing force and prepare your core for a supplier DFM review.
Four decisions to make before tooling
Engineering research by AxialFluxCore · Published · Updated and sources checked . Application recommendations below require part-specific confirmation.
Calculation method and its limits
A = π × (OD² − ID²) / 4
F (tf) = P (MPa) × A (mm²) / 9,806.65
Geometry reference = H / W
One MPa equals one N/mm², and one metric tonne-force equals 9,806.65 N. The default uses a solid annulus; an optional CAD projection replaces its area. Height does not enter this simple force equation.
The 600–800 MPa interval comes from Somaloy 5P process guidance. It represents two pressure scenarios, not a statistical confidence interval or a prescription for another powder grade.
For OD 150 mm and ID 90 mm, the envelope is 11,309.7 mm² and nominal force is approximately 692–923 tf. The actual projection may be smaller, but its reduction cannot be inferred from four dimensions.
Outside the model: powder fill height, density gradients, friction, separate punch loads, ejection force, press reserve, tool stress, tolerances, core losses and mechanical qualification. H is finished axial height; it is not powder fill depth. No geometry result is a manufacturing approval.
Three worked scenarios
Illustrative calculations using full-ring area and no press rating. These are not production case studies.
Baseline ring
OD / ID / H / W: 150 / 90 / 30 / 8 mm
692–923 tf · H/W 3.75:1
Start with CAD projected area and an actual supplier press rating.
Larger envelope
OD / ID / H / W: 250 / 150 / 30 / 8 mm
1,922–2,563 tf · H/W 3.75:1
Compare a larger press and segmentation; neither route is automatically mandatory.
Slender tooth
OD / ID / H / W: 150 / 90 / 60 / 4 mm
692–923 tf · H/W 15.00:1
Force is unchanged; fill and ejection need separate review. Force alone misses this change.
Turn geometry into a supplier drawing review
MPIF links long, thin sections to filling and density concerns and favors generous fillets. Its general PM guidance is a useful review checklist, not a qualified SMC tooth specification. Read the original design considerations.
REVIEW 1
Pressing and ejection
Annotate the pressing direction, back iron, slot depths and undercuts. Request a tool-motion sketch that shows how the green part is released and supported.
REVIEW 2
Tooth sections and radii
Dimension the narrowest section and the height of each step. Mark functional winding-clearance surfaces separately from radii that the toolmaker may adjust. Ask for evidence from comparable parts or trials.
REVIEW 3
Air-gap tolerance chain
Set datums and separate face flatness, axial height, runout and assembled position. Ask which dimensions are achieved as pressed, after heat treatment, after finishing and after assembly.
REVIEW 4
Segmentation and retention
Compare tooth interfaces, fixtures, retention method and inspection effort with the one-piece route. Include assembly scrap and tolerance stack-up in the quoted unit cost.
Record your dimensions, material candidates and open tooling questions in the RFQ worksheet before asking for a quotation.
Download the core RFQ worksheetSMC and laminated cores: compare the complete route
The public Höganäs axial-flux discussion describes SMC's isotropic properties and laminated alternatives, including wound constructions. Changing material without adapting the motor design can compromise performance. This table is an RFQ checklist; it does not rank costs or promise yield.
| Review point | SMC powder core | Electrical steel core |
|---|---|---|
| Process route | Powder compaction and grade-specific heat treatment; check the complete ejection sequence. | Cut or stamp and stack, or use a wound-core route suitable for the axial-flux topology. |
| Geometry review | Assess fill, thin tool members, steps, projected area and green-part handling. | Assess sheet direction, slot formation, burr control, stack fixation and assembly access. |
| Magnetic evidence | Request loss and permeability data for the selected grade, density and process. | Request data for the selected electrical steel, thickness and assembled core process. |
| Cost comparison | Quote tooling, cavities, cycle, finishing, inspection and assembled yield. | Quote strip use, cutting or stamping, stacking, joining, inspection and assembled yield. |
| Decision boundary | Consider when the geometry benefits from three-dimensional flux paths and can be tooled. | Keep as a candidate when its flux path, loss target and assembly route fit the design. |
Known inputs, unresolved risks and release evidence
Thermal qualification
Höganäs describes inorganic insulation on SMC particles. Its 5P heat-treatment parameter, up to 650°C, is a manufacturing condition, not a service rating. Coating context · 5P processing
Still unknown: permissible operating temperature for your complete part. Request strength, magnetic-loss and aging evidence at the intended duty.
Finishing and magnetic loss
A tight air-gap specification needs an agreed manufacturing and measurement route. Neither a universal as-pressed tolerance nor a mandatory chemical-etch step is established here.
Release evidence: finished-part dimensions and magnetic checks after the proposed process. Budget finishing and inspection in both prototype and production quotes.
Cost and structural life
This estimate contains no supplier capacity survey, tooling price, scrap benchmark or fatigue qualification. A nominal force figure cannot establish any of those outcomes.
Release evidence: a scoped quotation and tests for the actual retention, vibration, temperature and duty cycle. Revisit the route if those requirements dominate the design.
AFPM core DFM questions
Does a result within the press rating mean the design is manufacturable?
No. The comparison only divides pressure times projected area by the tonne-force conversion. Available tooling force, stroke, punch loads, ejection, density distribution and operating reserve still need a supplier review.
Which area should I take from CAD?
Use the projected silhouette of the pressed material normal to the assumed axial pressing direction. Exclude through-holes and through-slots. A blind winding slot over continuous back iron does not remove that back iron from the projection. Confirm multi-level parts and multiple cavities with the toolmaker.
What is the maximum SMC tooth aspect ratio?
There is no universal qualified limit established by the sources on this page. H/W helps describe the geometry, but powder flow, fill depth, section changes and tooling determine the process. Ask for a supplier limit tied to the chosen grade and representative trials.
Must every tooth have a draft angle?
No. The MPIF guidance distinguishes die-side walls from punch-formed features. Use the actual tool and ejection sequence to decide which surfaces need draft; a single angle for every slot is not a valid drawing rule.
Can machining be used to meet the air-gap tolerance?
Treat finishing as a process to qualify. Specify the finished face, datum, flatness and measurement method, then request dimensional and magnetic checks after the proposed finishing route. This page does not prescribe a universal machining allowance or chemical-etch treatment.
Can I use this for a radially pressed segment?
The ring model assumes axial pressing. Reorienting a segment changes the projection and load path. Ask the supplier to calculate that route from the drawing; entering its outer motor diameter here will not model it correctly.
Does the heat-treatment temperature define the service temperature?
No. A manufacturing heat treatment is not an operating-temperature rating. Request service-temperature and aging evidence for the actual powder, insulation, structural retention and duty cycle.
What should be included in a DFM inquiry?
Send a dimensioned drawing and CAD model, material candidates, motor duty and loss target, critical datums and tolerances, expected annual volume, and prototype quantity. Include the calculation inputs and ask the supplier to state which assumptions they have replaced with measured or qualified data.
Continue your core manufacturing review
Sources and review scope
Accessed 2026-09-20. Manufacturer data supports the named materials; MPIF covers general PM practice. Calculations and RFQ recommendations are this page's synthesis. We have not independently tested a stator or audited a supplier press fleet.
- MPIF / PickPM — Design Considerations
General powder metallurgy guidance on draft, fill, radii and tolerances. Not an SMC grade specification. Publication date not stated.
- Höganäs — Somaloy 5P process parameters
Manufacturer process guidance, including 600–800 MPa compaction for this product family. Publication date not stated.
- Höganäs / JMAG — Double-Sided Axial Flux Machines
Published 2022-11-17. Public introduction covers SMC coatings, processing and modular motor design. Login-only simulation results are not used here.
- Höganäs — Somaloy 3P material data (PDF)
Manufacturer grade-specific material and magnetic data; document copyright 2025. Sample properties do not certify a finished stator.
Prepare a CAD-based DFM assessment
Include your drawing, pressing direction, material candidates, annual volume and critical tolerances. Ask for a proposed tooling route, open assumptions and the sample evidence needed before production release.