This is the buyer-side version focused on RFQ quality and supplier comparability.
If you need design-level DFM details and process windows, read: Magnetic Circuit Design: DFM Engineering Playbook.
1. Define output at the measurement point
Do not start with magnet grade only. Start with measurable output:
- target output (Gauss, flux, pull force, torque)
- min/nominal/max tolerance window
- measurement position and orientation
- measurement temperature condition
If two suppliers test at different points or temperatures, the quote comparison is invalid.
2. Choose architecture before material upgrade
Common architecture choices:
- open magnetic path: lower complexity, more leakage
- partial return path: balance between performance and cost
- closed return path: stronger concentration, tighter geometry discipline
In many projects, architecture change has more impact than one magnet-grade upgrade.
3. RFQ thresholds to reduce ambiguity
Use practical threshold fields in RFQ:
| Field | Recommended clarity level |
|---|---|
| Air-gap definition | nominal value + tolerance + measurement reference |
| Thermal profile | continuous and peak value with dwell time |
| Drift allowance | allowed output drift over service life |
| Corrosion exposure | media type + exposure severity |
| Shielding requirement | whether nearby electronics require leakage control |
Leaving any of these open often causes quote assumption gaps.
4. Tolerance budget on magnetic-critical interfaces
Split dimensions by impact:
- highest priority: air-gap controlling features
- high priority: alignment datums for sensor/actuator interface
- lower priority: non-functional edges and cosmetic surfaces
This keeps machining spend focused where performance is sensitive.
5. Validation lines buyers should request
Before supplier recommendation is accepted, request:
- test fixture definition
- sample-size plan by stage (prototype/pilot)
- stress condition list (thermal, vibration, media)
- pass/fail criteria for both functional and dimensional outputs
If pass criteria are not written, validation disputes usually appear at pilot approval.
6. Quote comparison sheet for magnetic circuit proposals
When multiple proposals return, compare these columns:
- architecture assumption completeness
- return-path material definition
- validation scope coverage
- process-control readiness for critical features
- risk notes and fallback plan
This prevents decisions based on unit price only.
7. Typical buyer-side failure case
Observed pattern:
- RFQ specified only N-grade and outer size
- supplier A optimized for pull force, supplier B optimized for cost
- both quotes looked acceptable, but outputs were measured differently
- pilot comparison failed and project lost one cycle
Fix:
- define measurement point and condition in RFQ
- define drift allowance and environment profile
- require same comparison template for all suppliers
8. RFQ field checklist before release
Before issuing RFQ, confirm:
- output target with measurement condition is explicit
- architecture intent is stated (open/partial/closed)
- return-path material constraints are stated
- magnetic-critical datums are identified
- lifecycle and environment profile is complete
- validation deliverables are listed
- substitution and requalification rules are written
This is the minimum set for decision-grade quote comparison.
9. Read next in the workflow
- Deep engineering details: Magnetic Circuit Design: DFM Engineering Playbook
- Full RFQ structure: How to Specify a Custom Magnetic Assembly in Your RFQ
10. Advanced Deep Dive: Flux Leakage and the "Open Air" Fallacy
A common RFQ mistake is specifying "5000 Gauss at the surface" without defining what surrounds the magnet in the final application.
Case Study: Proximity Sensor Actuator Assembly
- The Mistake: A buyer approved a magnet that measured 5200 Gauss in open air on the factory floor. When installed in the actual machine, the magnet was mounted on a thick steel plate.
- The Physics: The steel plate acted as a massive magnetic short circuit (flux leakage path), pulling the field lines backwards. The surface Gauss reading in the application dropped to 1800 Gauss, failing to trigger the Hall sensor.
- The Fix: We redesigned the assembly to include a 2mm non-magnetic aluminum spacer between the magnet and the steel mounting plate, forcing the flux lines outward toward the sensor.
- Takeaway: Always specify the magnetic output in the installed condition, not in free space.
For a buyer-side pre-RFQ review, contact [email protected] or WhatsApp +8618857971991 (Open WhatsApp).
