High-frequency motor cores: when thin-gauge laminations beat thicker stacks

Designers know the theory: core loss, skin depth, Steinmetz, all that. What’s harder is this: at what point do thin-gauge laminations actually justify the extra cost and manufacturing pain?

This article is for that point. The grey zone where a 0.20 mm stator looks attractive, the tooling cost makes sales nervous, and someone in the room still wants 0.35 mm “because it always worked before.”

1. What “thin-gauge” really means in production, not in a datasheet

Let’s anchor some numbers first.

Typical practice today, looking across industrial and traction motors:

• Standard industrial motors still run laminations around 0.35–0.50 mm.
• Traction and high-speed machines have pushed down into the 0.20 mm class for mass production.
• Electrical steels around 0.10 mm exist and are tailored for high-frequency operation, but they’re used surgically where the business case is very tight.
• For cobalt alloys (Hiperco-type), vendors show lamination gauges around 0.15 mm as a good starting point in the few-hundred-Hz range, with 0.10 mm taking over as you move toward ~1–2 kHz.

So “thin” isn’t one magic number. It’s a band, and it shifts with:

• frequency
• flux density
• allowed temperature rise
• and how much your accountant is willing to suffer.

To compare options at a glance:

*Electrical frequency at the core, not necessarily line frequency.

These are not strict design rules. They’re the ranges where data sheets, academic studies and real motors start to agree.

2. Why thin-gauge helps at high frequency (without re-teaching electromagnetics)

You already know the punchline: eddy current loss in a lamination goes roughly with thickness² and frequency² for a given material and flux swing.

So if you drop thickness from 0.35 mm to 0.20 mm:

• loss per kilogram from eddy currents falls by roughly [(0.20 / 0.35)² ≈ 0.33]
• which is about ⅓ of the previous eddy-current loss, all else equal.

In real cores, hysteresis and “excess” loss blunt that ideal, but test curves still show the same direction: thinner laminations consistently give lower total core loss compared to thicker ones at the same grade and flux density.

What changes as you push frequency up:

• At 50–60 Hz, core losses might be ~20–25 % of total machine losses.
• At several hundred Hz, with similar current loading, core losses can move close to the top of the loss list.
• Above that, if you don’t go thinner, thermal design starts fighting back: forced cooling, higher-grade insulation, more copper to spread heat.

So thin-gauge laminations are less about fashion and more about where eddy-current loss stops being a rounding error and starts rewriting your thermal budget.

3. Where thin-gauge wins clearly

3.1 Frequency bands where thin-gauge is almost mandatory

Take published guidance around cobalt-based alloys for high-frequency machines:

• Around 300–800 Hz, ~0.15 mm laminations are often an efficient starting point.
• Around 800–1800 Hz, 0.10 mm starts to outperform in core loss.

Similar patterns show up in thin-gauge silicon steel data from electrical steel producers: grades around 0.10–0.20 mm are positioned specifically for high-frequency use because they reduce loss at higher induction levels.

If your motor spends real time in those bands under load — not just transient testing — thick laminations will cost you:

• higher iron loss
• hotter cores
• more cooling hardware than you probably wanted

At that point, arguing for 0.35 mm purely on material price is usually short-sighted.

3.2 Compact, high-torque, high-speed machines

EV traction motors, integrated starter-generators, oil-cooled e-axles, aerospace generators — all of them compress power into tight envelopes.

In these machines:

• space for copper and cooling is limited
• allowable temperature rise is constrained by the weakest component (often insulation or magnets)
• duty cycles are harsh; partial load is not always gentle

Thin-gauge laminations, especially high-grade non-oriented SiFe around 0.20 mm and below, are widely adopted in these sectors because they support higher base speeds and field-weakening ranges before loss and temperature hit their limits.

In short: once you’re in high-speed, high-power-density territory, thin-gauge is not a “premium option”; it’s part of the baseline stack for competitiveness.

4. Where thicker stacks still make sense

Thin laminations are not a universal answer. There are honest cases where thicker stacks win the project.

4.1 Moderate-performance, cost-driven drives

If the motor:

• runs near 50–100 Hz electrical most of its life
• has relaxed efficiency targets
• works in environments where a few extra Kelvin of core temperature are manageable

Then 0.35 mm or even 0.50 mm steel may keep the BOM and tooling costs under control without breaking any spec.

Some steel producers even argue that, for mild hybrids or short-range electrification, it can be rational to accept slightly lower efficiency via 0.30–0.35 mm gauge, in exchange for lower material cost and reduced battery capacity requirements.

The business case can dominate here, not physics.

4.2 High-stress rotors

At very high mechanical speeds, rotor cores have another job: not exploding.

You see designs with:

• thicker laminations
• or even solid steel rotors with careful slotting
• mechanical sleeves, shrink-fit constructions

Research on thick-lamination rotors shows that, for large machines, thicker plates combined with manual insulation can be an acceptable compromise to handle stress and manufacturability, especially when you’re already using high-strength steels and advanced machining (laser cutting, etc.).

So for rotors in the danger zone of mechanical stress, electromagnetic optimum is sometimes dialed back. You pay some extra iron loss to gain survival margin.

5. A practical decision path: when thin-gauge actually beats thicker stacks

Theory is nice, but B2B engineering usually comes down to: which option does the job with less risk at acceptable cost?

Here’s a compact way to think through lamination thickness for high-frequency cores.

Step 1 – Fix your real operating frequency

Not the catalog speed. The actual electrical frequency range where:

• torque is high
• duty cycle is substantial

If more than ~30–40 % of energy is processed above 300–400 Hz, thin-gauge options deserve serious attention.

Step 2 – Look at iron loss share, not just efficiency

Use your existing simulations or test data and split losses into:

• stator core
• rotor core
• copper
• mechanical

If core losses are:

• < 15 % of total → thickness is probably not your main lever.
• 15–30 % → you’re in the region where thinner laminations can unclog the thermal path.
• > 30 % → something is misaligned: flux density, thickness, grade, or all three.

Thin-gauge laminations are most powerful when iron loss is a top-two contributor.

Step 3 – Check mechanical and process constraints early

Thin laminations introduce non-trivial issues:

• Burr control becomes critical. Excessive burr destroys effective insulation between laminations and quietly eats the loss savings.
• Stacking factor drops; more sheets for the same core height mean more handling and more opportunities for coating damage.
• Press tooling must be precise enough; thin-gauge often demands tighter clearances and more frequent maintenance.
• Stack assembly (welding, bonding, interlocking) has to avoid distortions in tall stacks of very thin sheets.

If your supply base or factory isn’t ready for that, the theoretical gains might never arrive at the test bench.

Step 4 – Do a back-of-envelope trade-off

Even without full finite-element runs, you can compare options:

• estimate iron loss with vendor curves for two thicknesses at your main flux density
• estimate how much heat that removes (W/kg × core mass)
• translate that into cooling simplification or efficiency gain

Then ask: Is that worth the extra cost of material + tooling + process risk?

If the answer is “yes, but only barely,” it might still be smart to qualify both thicknesses — one as a performance version, another as a cost-down version.

6. Design tips that usually pay off with thin-gauge stacks

Some small decisions have outsized effects when you move into thin laminations.

• Keep flux density realistic. Many high-frequency grades are specified for lower loss at moderate induction, not heroic 1.9–2.0 T. Check the recommended operating window for the grade you actually plan to buy.
• Watch local hotspots. Even thin laminations can show ugly local loss where tooth tips or bridges push flux density far above the average.
• Balance stator and rotor choices. A super-thin stator with a “cheap” rotor stack may move loss into the rotor and into places where cooling is worse.
• Align insulation and lamination handling. Thin-gauge often relies on more advanced coatings; stacking, welding, and slot wedge designs should avoid scraping that coating off.
• Define inspection rules upfront. Decide early how you’ll measure burrs, stacking factor, and lamination flatness on incoming parts, especially when switching supplier or tool.

This is where a lamination supplier with actual high-frequency production experience earns their margin.

7. Questions to ask your lamination-stack supplier

When you’re sourcing high-frequency stator and rotor cores, your RFQ and technical Q&A can quietly decide whether thin-gauge succeeds or fails. Some practical questions:

1. Which thickness ranges do you routinely cut and stack for >400 Hz work?
2. What’s the typical burr height you achieve at that gauge, and how do you measure it?
3. Can you share core-loss test results for the same grade in at least two thicknesses at your frequency and induction?
4. What stacking methods do you recommend for my stack height and slot geometry?
5. How do you control lamination tilt and coaxiality in tall, thin stacks?
6. What’s the usual scrap rate at this thickness, and who absorbs that cost under our commercial terms?
7. Do you have experience with bonding / adhesive-coated laminations for this gauge, or only traditional interlock/weld?
8. How do you qualify a new tool for thin-gauge production? What run length, what measurements?

Suppliers that can answer these concretely are more likely to deliver the theoretical thin-gauge benefits in real hardware.

8. Summary for busy teams

If you skimmed everything else, keep this:

• At several hundred Hz and above, lamination thickness becomes a primary driver of core loss and thermal behavior, not a minor detail.
• Thin-gauge (around 0.20 mm and below) tends to win in: EV traction, aerospace, compact high-speed machinery, anything with strict efficiency or power-density contracts.
• Thicker laminations still have a place where cost, mechanical stress, or relaxed performance targets dominate.
• The real decision is not “thin vs thick,” but how often your motor lives in the high-frequency, high-flux zone, and whether your manufacturing system is ready for thin-gauge reality.

FAQ: High-frequency motor cores & lamination stacks