A motor manufacturer may receive electrical steel that meets its specified core-loss requirements, yet find that the finished stator has higher losses than the design model predicted.

Part of the difference may come from manufacturing. Punching can leave residual stress near cut edges, burrs can create electrical contact between laminations, and welding or housing assembly can change the core's magnetic behavior.

Finding the cause requires looking at the manufacturing steps and, where available, measurements taken between them.

1. Where Manufacturing-Related Core Loss Begins

Electrical steel core-loss data is obtained under specified magnetic conditions, commonly using standardized methods such as the Epstein frame or single sheet tester (SST). It provides a reference for material performance before motor-core manufacturing.

Punching, stacking, welding, and housing assembly can introduce changes that are not represented by the original material test. Some affect the steel's magnetic properties; others may create additional electrical paths between laminations.

Research published in IEEE Transactions on Energy Conversion, Effects of Manufacturing Processes on Core Losses of Electrical Machines, examined these manufacturing effects in an industrial motor.

Before attributing a loss increase to manufacturing, confirm that the measurements use comparable loss components and test conditions.

2. How Cutting Damage Can Increase Core Loss

Punching subjects electrical steel to concentrated mechanical forces near the cutting edge. The resulting plastic deformation, strain hardening, and residual stress can alter the magnetic behavior of the affected region.

Under certain excitation conditions, this region may have lower magnetic permeability and higher hysteresis-related losses than the relatively undamaged steel farther from the edge.

The extent of degradation varies with the steel grade, cutting geometry, tool condition, and punching parameters.

A 2023 review published in Energies, A Review on the Effect of Electrical Steel Manufacturing Processes on the Performance of Electric Machines, discusses the effects of cutting and other manufacturing processes on electrical steel performance.

Why Narrow Stator Teeth Deserve Attention

Narrow stator teeth can be particularly sensitive to cutting damage because a larger proportion of their magnetic cross-section lies near processed edges.

Consider two stators made from the same electrical steel grade, one with relatively wide teeth and the other with narrow teeth. If punching produces a similar damaged region along their edges, that region occupies a greater proportion of the narrower tooth.

The same steel grade and nominal thickness can therefore show different sensitivity to cutting damage in wide-tooth and narrow-tooth stators.

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Comparison of laminated stator teeth illustrating how cutting-edge damage can affect magnetic properties and increase core loss, particularly in narrow teeth.

3. How to Distinguish Burr-Related Loss from Cutting Stress

Cutting damage and lamination burrs are related to the same manufacturing process, but their effects on core loss are different.

Residual stress changes the magnetic properties near cut edges. Burrs present a separate risk: they can bridge the insulation between adjacent laminations, creating conductive contacts that allow additional circulating currents.

Depending on the contact paths, these currents may increase local losses and cause hot spots.

A study published in IEEE Transactions on Magnetics, Evaluation of Loss Generated by Edge Burrs in Electrical Steels, investigated artificial short circuits at lamination edges. The study found that the location of interlaminar electrical contacts, as well as their presence, can influence total power loss.

What Burr Inspection Can and Cannot Show

Visible burrs are useful evidence of cutting quality, but they do not reveal the full magnetic condition of a lamination.

A sheet with minimal visible burrs may still have a magnetically degraded region near its cut edges. Conversely, a visible burr does not necessarily create a significant loss increase unless the resulting electrical contacts form current paths.

4. Identifying Loss Changes After Welding and Housing Assembly

Welding and Housing Assembly

Welding can affect core loss through localized heating, residual stress, and electrical contact between laminations. The location of the welds matters because the affected regions are not the same in every stator design.

Housing assembly introduces a different source of stress. When an interference or shrink fit is used to install the stator into its housing, the resulting mechanical pressure can change the magnetic behavior of the laminated core.

These processes affect the core in different ways. Where practical, magnetic measurements before and after welding or housing installation can help establish when additional losses appeared.

Evidence from Manufacturing Research

An Aalto University study investigated cutting, welding, and shrink-fitting effects in a 37 kW induction motor.

At the studied rated condition, the researchers attributed approximately 10%, 7%, and 6% additional loss to these respective manufacturing stages, with a combined increase of about 23%.

These percentages were reported for the 37 kW motor under the studied operating condition and should not be used as general loss allowances for other designs.

5. How to Trace Additional Core Loss Through Manufacturing

A finished-core loss measurement can show that performance differs from expectations, but it may not identify where the difference originated.

Before investigating individual processes, engineers need to check that the measured loss components, excitation conditions, and normalization methods are comparable. A completed motor's efficiency result, for example, includes losses beyond the iron core and requires suitable loss separation.

Compare Manufacturing Stages

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Motor stator manufacturing stages from electrical steel coils through punching, lamination stacking, welding, and housing assembly.

Where suitable measurements are available, comparing the core at selected manufacturing stages can help narrow down the source of additional loss.

Manufacturing Stage	What to Check	Possible Indication
Material receipt	Steel grade, core-loss data, and specified test conditions	Whether the supplied material meets the agreed requirements
Cutting and punching	Tool condition, cutting parameters, and tooth geometry	Possible cutting-induced magnetic degradation
Lamination stacking	Burrs, insulation condition, and interlaminar electrical contact	Possible additional current paths
Welding or joining	Joint location, welding conditions, and magnetic measurements before and after joining	Possible joining-related loss changes
Housing assembly	Fit conditions and measurements before and after installation	Possible effects of assembly stress

If a loss increase appears after punching, residual stress and interlaminar electrical contact are two possible causes. Separating their contributions may require controlled tests or validated models.

A manufacturer may start with measurements before and after the production step most likely to have introduced the additional loss, rather than testing every stage.

6. What the Steel Supplier Can Verify

Material test records and manufacturing-stage measurements answer different questions.

Electrical steel suppliers can document the material grade, dimensions, coating, and magnetic properties of supplied coils. These records help manufacturers check material compliance before processing.

For HWHG electrical steel coils, product labels carry information such as grade, dimensions, coating, core loss, and magnetic induction. Inspection certificates provide more detailed material and test records, including applicable magnetic property results and coil identification.

1780384596857-HWHG Electrical Steel Quality Verification Label.webp

HWHG electrical steel coils illustrated with material labels and inspection certificates for verifying grade, dimensions, coating, and magnetic properties.

These records support material verification. Additional losses introduced during punching, stacking, welding, or housing assembly require investigation during motor-core manufacturing.

For more detail on material requirements, see Electrical Steel Grade vs. Actual Core Loss: What Should Buyers Specify?.

For standardized magnetic measurement methods, see Epstein Frame vs Single Sheet Tester.

Conclusion

When electrical steel meets its specified requirements but finished-stator core loss exceeds the design prediction, replacing the material is not necessarily the first step.

Check the production stage where the additional loss may have appeared. Comparable measurements taken before and after that stage can provide a starting point for identifying the cause.

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