Concentrated vs distributed windings: how lamination geometry changes

When a customer says, “We may switch from distributed to concentrated winding, but keep the lamination stack basically the same,” that is usually where the drawing starts to drift.

Because winding choice does not stay in copper. It moves into steel.

For lamination stacks, the real change is not academic. It lands in slot area. Tooth width. Tooth-tip shape. Back-iron reserve. Sometimes segmentation. Sometimes skew. Sometimes nothing dramatic at first glance, then one small flux bottleneck turns the whole stack into a thermal problem.

That is how we look at it on the factory side.

The first mistake: treating winding choice as a winding-only decision

If the winding topology changes, the stator lamination geometry has to be rebalanced. Not always redrawn from zero. But rebalanced, yes.

A concentrated winding usually pushes the design toward a more local magnetic loading pattern around each tooth. The end turns get shorter, which is useful, but the active steel now has to absorb a different set of compromises. Local saturation margins matter more. Harmonic content matters more. Slot opening decisions stop being cosmetic.

A distributed winding spreads the magnetic action across more slots. The air-gap field is usually cleaner. Geometry becomes less sensitive in one place and more constrained in another. You gain smoothness, then pay with longer end turns, more copper outside the stack, and often less freedom in coil insertion and insulation packing.

So the lamination stack changes either way. The only question is where.

What actually changes in the lamination stack

For most programs, we see five geometry zones move first.

1. Slot area stops being a neutral number

With concentrated windings, teams often expect the shorter end turns to solve the copper side by themselves. Sometimes they do. Sometimes they simply create room to push current density harder, which means the slot window gets used more aggressively. Then the lamination is forced to decide who loses space: the tooth, the back iron, or the insulation margin.

With distributed windings, slot area is still critical, but the geometry pressure is different. The slot is part of a broader magnetic pattern, not a single-tooth event. That usually gives a more forgiving flux distribution inside the stack, while the copper penalty shifts outside the core into longer coil overhangs.

The practical point is simple: identical slot area does not mean equivalent lamination behavior after a winding change.

2. Tooth width becomes a magnetic control lever

In concentrated winding stators, the tooth is busy. It carries the coil. It shapes local permeance. It reacts harder to tooth-tip decisions. If the tooth is too slim, the design may look fine at nominal load and then fold at overload or field-weakening corners. If the tooth is too wide, slot fill and insertion effort start pushing back.

So we do not size the tooth from slot fill alone. We size it from local flux density margin first, then see how much copper the window can still accept without turning the stack into a stamping or winding headache.

Distributed winding laminations are different. The tooth set works more like a group than like isolated high-duty teeth. That often reduces local tooth-tip stress, but it does not mean tooth geometry can be relaxed. It means tooth width and slot pitch must stay aligned with winding factor targets, vibration behavior, and the insulation build that production can actually hold.

3. Tooth-tip geometry matters more than many drawings admit

A lot of stator drawings show the tooth tip as if it is just the end of the tooth. It is not. It is a field-shaping feature.

In concentrated winding lamination stacks, small tooth-tip changes can alter saturation onset, slot leakage, cogging behavior, and harmonic coupling to the rotor. Not by a little. Enough to change whether the motor runs acceptably across the whole duty range or only looks good in one operating island.

That is why we pay close attention to:

• tooth-tip width,
• slot opening width,
• tooth-tip radius,
• and the consistency of these details through the full stack height.

Distributed winding designs are usually less sharp-edged here, but still not free. A wider slot opening may help one manufacturing issue and quietly create another electromagnetic one. A narrow opening may help field shape and then complicate winding insertion or slot liner control.

So the tooth tip is not a clean-up detail. It is part of the main geometry.

How concentrated windings usually push lamination geometry

This is the pattern we see most often in concentrated winding programs.

The stack starts moving toward a tooth-centered geometry. Wider magnetic duty per tooth. Greater sensitivity to slot opening. Greater interest in segmented stator concepts. Stronger pressure on local saturation checks. And more care around rotor-side harmonic loss, because the winding is not giving you a naturally smooth field for free.

That does not mean concentrated winding is the “high saturation” option by default. Bad wording. What it means is the geometry has less room to be casual. One tooth feature can change several outputs at once.

In practice, concentrated winding lamination stacks often benefit from:

• tighter control of tooth-tip profile,
• closer review of back-iron thickness near peak loading,
• deliberate slot-opening tuning rather than copy-paste dimensions,
• and manufacturing routes that support high fill factor without distorting the tooth.

This is also where segmented lamination stacks become more attractive. Not as a trend. As a production answer. If the winding strategy rewards short end turns and high fill, a segmented stator may stop looking optional.

How distributed windings usually push lamination geometry

Distributed winding changes the stack in a calmer way, but not a cheaper one.

The lamination often moves toward more slots, narrower effective magnetic loading per tooth, and a more even circumferential field. That helps waveform quality and usually reduces the amount of geometry trickery needed to control local magnetic stress.

But then the copper package expands outside the core. End-turn length rises. Copper mass rises. Assembly space changes. Thermal decisions move beyond the lamination, yet the lamination still has to carry the right slot geometry for insertion, insulation, and stack rigidity.

So distributed winding stacks often end up with:

• stricter slot repeatability across many slots,
• more sensitivity to cumulative stamping tolerance,
• less tolerance for burr-related insulation risk,
• and more design time spent balancing electromagnetic smoothness against winding manufacturability.

It is a smoother system. Not a simpler one.

A direct comparison for lamination stack design

The part many buyers miss: lamination geometry follows the winding process too

Some geometry decisions are electromagnetic. Some are production-driven. Most are both.

A concentrated winding stack may look efficient on paper, then fail commercially because the tooth shape is too fragile in stamping, or because the stack build creates too much variation at the slot opening, or because the chosen interlock location steals steel from the wrong place.

A distributed winding stack may look conservative, then underperform in manufacturing because the slot count pushes tolerance stacking, or because the winding insertion method forces a slot profile that was never reviewed for tooling life.

This is why we review lamination stacks with the winding route in the room. Always. Hand insertion, needle winding, preformed coils, segmented tooth winding, welded stack, bonded stack, interlocked stack. These are not downstream notes. They change the steel.

What we usually tell customers before freezing the lamination drawing

If you are evaluating concentrated vs distributed windings, the faster question is not “which winding is better?”

It is this:

Which geometry penalty are you more able to control in production?

If your program can manage local tooth sensitivity, harmonic cleanup, and possibly segmented assembly, concentrated winding may give a strong lamination-stack answer.

If your program values smoother magnetic behavior, broader slot distribution, and can accept the copper and package cost outside the core, distributed winding may keep the stator geometry more forgiving.

Neither choice is generic. The same outer diameter and stack length can behave like two different products once the winding topology changes.

That is why we do not quote lamination stacks from slot count alone. We want the winding direction, slot/pole combination, target fill strategy, and the real process route before we call a drawing mature.

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