Oct.07,2026
Reducing eddy current losses in electric motor stator and rotor cores requires more than selecting thinner steel. At Onlink, we solve the problem through a controlled process covering electrical steel selection, lamination design, punching quality, insulation coating, core stacking, and final testing. By following the steps below, motor manufacturers can reduce unnecessary heat generation, improve efficiency, and create a repeatable production process with clear inspection points.
When an alternating magnetic field passes through a solid conductive core, circulating currents are induced inside the steel. These currents are known as eddy currents, and they generate heat instead of useful mechanical output.
The total iron loss of a motor core is generally divided into:
Eddy current loss becomes especially important in:
For a simplified lamination model, eddy current loss is related to:
[ Pe \propto \frac{B{max}^2 f^2 t^2}{\rho} ]
Where:
This relationship explains why reducing lamination thickness and increasing interlaminar electrical resistance are central to controlling core loss.
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The following manufacturing sequence provides a practical solution for both new motor designs and existing core-loss problems.
The first decision is the grade and thickness of the electrical steel. Standard low-carbon steel is usually unsuitable for efficient AC motor cores because its resistivity and magnetic properties do not provide adequate loss control.
We normally evaluate:
For most rotating electric motors, non-oriented silicon steel is selected because the magnetic flux changes direction around the stator and rotor.
A thinner lamination can significantly reduce eddy current loss, but it may also increase:
For this reason, we recommend selecting the thinnest commercially practical material that meets the motor’s frequency, torque, thermal, and cost requirements.
Lamination thickness directly affects eddy current loss because the loss increases approximately with the square of thickness.
For example, changing from 0.35 mm steel to 0.20 mm steel can substantially reduce eddy current circulation, provided the material grade and insulation system remain suitable.
Dimensional control is equally important. Variations in:
can create local flux concentration and increase iron loss.
As an Electric Motor Core Parts Manufacturer, Onlink can control critical stamping dimensions to approximately 0.01 mm where the product drawing, material thickness, and tooling design permit. We recommend identifying critical-to-function dimensions before tooling begins rather than applying the same tolerance to every feature.
Each lamination must be electrically separated from the next. The insulation coating prevents current from circulating through the entire core stack.
Common electrical steel coating systems include:
The coating should provide:
A coating that is too thin, damaged, contaminated, or removed during forming can create conductive bridges between laminations. These bridges increase circulating current and localized heating.
Recommended controls include:
The exact acceptance value depends on the material supplier, coating type, lamination geometry, and motor specification. It should be defined in the purchase specification instead of assumed from a general catalog value.
Burrs are one of the most common causes of increased eddy current loss in stamped stator and rotor laminations. A burr can cut through the insulating coating and electrically connect adjacent laminations.
Burr-related problems often result from:
To reduce burrs, we recommend:
A practical target may be a burr height below 10–20% of the lamination thickness, but the correct limit must be confirmed through the customer drawing and core-loss validation. For a 0.20 mm lamination, even a small burr can become electrically significant.
Onlink uses dimensional inspection and production sampling plans to identify burr growth before it affects complete core assemblies. For high-risk programs, customers may request 100% visual inspection of critical edges and documented first-piece approval.
Even correctly stamped laminations can develop excess losses during assembly. Scratches, impact marks, excessive pressure, and incorrect interlocking can damage the coating.
During stacking, control:
Avoid uncontrolled welding across the core because welds create low-resistance electrical paths. If welding is necessary, use a qualified pattern and verify that the heat-affected zone does not create unacceptable core loss.
Bonded cores can reduce mechanical damage and improve dimensional stability. However, adhesive selection must account for:
Material and manufacturing improvements cannot compensate for an overloaded magnetic circuit. If the stator teeth or rotor back iron operate near saturation, the motor can experience higher iron loss, noise, vibration, and temperature rise.
During electromagnetic design, review:
Reducing peak flux density may require a larger core, wider teeth, or improved winding design. Although this can increase material usage, it may reduce operating temperature and improve efficiency over the motor’s service life.
For inverter-fed motors, analyze high-frequency harmonics rather than evaluating only the fundamental frequency. PWM voltage waveforms can produce additional rotor surface losses, magnet losses, and localized lamination heating.
Skewing the stator or rotor slots can reduce cogging torque, torque ripple, and certain space harmonics. It does not replace proper lamination insulation, but it can reduce harmful flux pulsations that contribute to additional core loss.
Typical skew considerations include:
The best skew angle must be determined through electromagnetic simulation and prototype testing. Excessive skew can reduce average torque and increase manufacturing cost.
A reliable core-loss reduction program should connect material control, stamping, stacking, and testing. The following table summarizes key checkpoints.
| Process stage | Main risk | Recommended control | Useful evidence |
|---|---|---|---|
| Electrical steel purchasing | Incorrect grade or thickness | Verify material certificate and grade | IEC 60404-8-4, DIN EN 10106, ASTM A677/A677M where applicable |
| Tooling preparation | Excessive burrs | Check punch-die clearance and tool condition | First-piece inspection |
| Lamination stamping | Dimensional drift | Use CMM, optical inspection, or profile measurement | Critical dimensions controlled to about 0.01 mm where specified |
| Coating condition | Interlaminar short circuits | Inspect coating and test resistance | Supplier specification and internal test method |
| Core stacking | Misalignment or coating damage | Control stack height, pressure, orientation, and skew | Stack-height report |
| Core assembly | Welding or bonding shortcuts | Qualify weld pattern or adhesive process | Process approval record |
| Final inspection | Undetected assembly defects | Check dimensions, runout, insulation, and appearance | 100% visual inspection when contractually required |
The applicable standards should be agreed upon before production. Electrical steel requirements may be referenced through IEC 60404-8-4, DIN EN 10106, ASTM A677/A677M, or the customer’s designated material standard. Motor performance and loss testing may be evaluated using IEC 60034-2-1, depending on the motor type and test configuration.
A process change should always be confirmed through testing. We recommend comparing a baseline core with the improved version under the same test conditions.
Measure:
When comparing two materials or processes, use the same sample dimensions, frequency, flux density, and test procedure. Otherwise, the results may not be comparable.
This test checks whether adjacent laminations remain electrically insulated. It is particularly important after:
Test frequency and acceptance criteria should be defined by the customer specification or validated internal method.
Inspect:
For high-volume production, statistical process control can identify gradual tool wear before it produces a noticeable increase in motor temperature or no-load current.
Very thin laminations are more vulnerable to distortion and handling damage.
Solution: Use dedicated tooling, controlled stacking fixtures, protective packaging, and lower-impact transfer methods. Begin with prototype stamping before committing to mass production.
A visual check may not detect coating damage between laminations.
Solution: Combine burr-height measurement with interlaminar resistance testing and core-loss comparison. Inspect the most vulnerable areas, especially tooth tips and slot openings.
Welds can electrically bypass insulation and increase circulating current.
Solution: Minimize weld length, isolate weld locations where possible, validate the welding sequence, and compare welded and bonded samples through core-loss testing.
A certificate may describe the steel grade but not the final stamped-and-stacked core condition.
Solution: Treat the material certificate as an incoming control, not final proof. Validate the completed core using dimensional, electrical, and performance tests.
A motor that performs well on a sine-wave test may run hotter with a PWM inverter.
Solution: Include the actual inverter switching conditions in electromagnetic simulation and prototype validation. Review rotor surface loss, harmonic flux, magnet heating, and bearing-current risk.
We use a combination of engineering and quality tools to shorten troubleshooting time:
An effective supplier should also provide:
Onlink provides a practical communication process for international projects, including engineering review and a target response within 24 hours for technical questions when complete drawings and specifications are supplied.
Selecting an Electric Motor Core Parts Manufacturer is not only a purchasing decision. It directly affects motor efficiency, temperature rise, noise, reliability, and warranty risk.
Onlink supports motor manufacturers with:
Our approach is to review the complete magnetic and manufacturing chain rather than focus only on the steel grade. This helps customers avoid a common problem: selecting low-loss material but losing the benefit through burrs, coating damage, poor stacking, or excessive harmonic flux.
To apply How to Reduce Eddy Current Losses in Electric Motor Stator and Rotor Cores to an active project, follow this sequence:
The most effective answer to How to Reduce Eddy Current Losses in Electric Motor Stator and Rotor Cores is a complete process: use suitable non-oriented electrical steel, reduce lamination thickness where practical, preserve interlaminar insulation, control burrs, protect the stack during assembly, and validate the finished core under real operating conditions.
As an Electric Motor Core Parts Manufacturer, Onlink helps customers turn these principles into measurable production controls, including approximately 0.01 mm dimensional capability where specified, 100% visual inspection options for critical parts, documented testing, and 24-hour technical response targets. Contact Onlink with your motor drawings, steel grade, operating frequency, and core-loss target so we can recommend a controlled, efficient path from prototype to reliable mass production.
