Motor Laminations 101: A Practical Guide for Engineers, Product Designers, and Procurement

Every electric motor project starts with the same nagging questions. How do we hit our efficiency target without blowing the budget. Which lamination material and thickness will keep losses down at our operating speed. Is stamping worth the tooling cost or should we laser cut and keep things flexible. If you’re weighing trade‑offs between lamination material, thickness, and manufacturing process, you’re in the right place.

This guide uses a simple framework: Problem → Explain → Guide → Empower. I’ll lay out the physics in plain English, then walk you through material and process choices with honest pros and cons. You’ll leave with a short checklist you can take to your supplier and a clear path to a sound, defensible decision.

In a rush. Skip to the “Engineering Takeaway” at the end for a concise summary and next steps.

In This Article

• Why Lamination Choice Is Critical to Your Motor’s Success
• Core Losses Explained: Eddy Currents, Hysteresis, and Frequency Effects
• Material Selection Guide: Silicon Steel, Cobalt Alloys, Amorphous, and More
• Manufacturing & Assembly: Stamping, Laser Cutting, Bonding, Interlock, Welding
• Best Fit by Application: Industrial Induction, BLDC/PMSM, High‑Speed Aerospace, Transformers
• Cost, Quality, and Supply Chain: Tooling, Coatings, Tolerances, and Testing
• Specification Checklist and Data‑Driven Selection
• Engineering Takeaway: What to Do Next

Why Lamination Choice Is Critical to Your Motor’s Success

The problem you face is simple to state and tough to solve. You need high motor efficiency, acceptable thermal performance, reliable torque production, and a realistic unit cost. The core material and lamination stack drive each of those outcomes. The wrong pick shows up as excess heat, noisy torque, and wasted watts. The right pick quietly delivers performance every day.

Here’s why laminations matter so much:

• Core loss dominates efficiency at moderate to high speeds. It shows up as heat in the stator and rotor.
• Permeability and saturation set your flux density ceiling. That sets torque density and package size.
• Thickness and coating quality control eddy current loss and stack factor. You can’t hit targets without optimizing both.
• Manufacturing method alters magnetic properties. Cutting processes create burrs and heat‑affected zones. Assembly methods can create shorted turns in the stack if you’re not careful.

When you optimize laminations, you lower copper loss indirectly. Less core loss means lower temperatures which increases copper conductivity and raises efficiency. Better laminations can also let you shrink the frame or reduce magnet mass. Small choices ripple through the whole design.

If you want a quick analogy, think about the “bulletproof” reputation of Toyota’s cast‑iron 2JZ inline‑six. The iron block, over‑built bottom end, and sensible engineering gave it headroom for power and life. Well‑chosen laminations play that same role in an electric motor. They set the foundation for efficiency, torque density, and durability.

Core Losses Explained: Eddy Currents, Hysteresis, and Frequency Effects

Let’s break down the physics with a simple picture.

• Magnetic flux is like water flowing through a sponge. Permeability tells you how easily the flux passes. High permeability acts like an open channel.
• Hysteresis is the energy you spend flipping magnetic domains back and forth each cycle. Imagine bending a paper clip over and over. It warms up from internal friction. Materials with low coercivity lose less energy per cycle.
• Eddy currents form when a changing magnetic field induces circular currents in the steel. Think of them as tiny unwanted whirlpools in a river. Those whirlpools waste energy as heat.

Thinner, insulated laminations chop those whirlpools into tiny eddies. Smaller loops mean less wasted energy. That’s the core reason laminations exist.

Key terms in practical language:

• B‑H curve: A graph that shows how the material responds to a magnetic field. It tells you how much flux density (B) you get for a given magnetizing field (H).
• Permeability: How easily flux flows through a material. High permeability means you get more flux for the same MMF.
• Coercivity: The material’s resistance to being demagnetized or remagnetized. Lower is better for reducing hysteresis loss.
• Saturation flux density (Bsat): The ceiling for usable flux. Push past it and your torque gains flatten while losses climb.

Frequency matters, a lot:

• Hysteresis loss scales roughly with frequency and to a power of peak flux density (often approximated as proportional to f·B^n with n around 1.6 to 2 depending on the alloy).
• Eddy current loss scales roughly with the square of thickness and frequency (∝ t^2·f^2) and with B^2. Halve the thickness and you cut eddy loss by about four at a given speed and flux.

Insulation coatings between laminations create electrical resistance. That resistance breaks up eddy currents and lowers loss. Coating class and quality matter because they set interlamination resistivity and stacking factor. You want enough insulation to block currents without killing the effective iron fill.

Stacking factor is the ratio of iron to total stack thickness. More insulation and burrs reduce it. Lower stacking factor reduces effective permeability and torque density. Specify both coating type and stacking factor so your model matches reality.

If you want to dig into standards, the IEC 60404 series defines test methods and material designations for soft magnetic materials. IEEE Std 112 covers methods for motor efficiency testing. Those documents anchor your lab results in accepted practice.

For foundational terms and an overview of materials, many teams start with a primer on electrical steel laminations. It helps everyone speak the same language before you lock specifications.

Material Selection Guide: Silicon Steel, Cobalt Alloys, Amorphous, and More

No single material wins every application. Your operating frequency, temperature, size, and cost targets will narrow the list quickly. Here’s a clear, unbiased overview.

Non‑Oriented Silicon Steels (NOES, M‑grades like M19, M27, M45)

Best for general‑purpose motors at 50/60 Hz through a few hundred Hz electrical.

• Pros:
• Balanced permeability and loss at industrial frequencies
• Wide availability with well‑understood supply chains
• Reasonable cost and strong mechanical properties
• Many thickness options: ~0.35 mm to 0.20 mm and thinner for higher frequency

• Cons:
• Loss rises fast at high frequency relative to specialty alloys
• Lower saturation than cobalt alloys, so torque density may be limited

• Use when:
• You build induction motors, BLDC/PMSM for appliances, HVAC, pumps, and industrial drives below a few hundred electrical Hz
• Cost and manufacturability matter most

If you need a refresher on grades and their trade‑offs, see this overview of silicon steel laminations.

Grain‑Oriented Electrical Steel (GOES)

Optimized for transformers with flux largely in one direction. Motors see rotating flux that crosses the rolling direction. That negates the grain advantage and can raise losses in the transverse direction.

• Pros:
• Very low loss along the rolling direction
• Cons:
• Poor transverse performance for rotating machines
• Use when:
• You design transformers or hybrid components with strong uniaxial flux paths

High‑Silicon Non‑Oriented Steels (2–3.2% Si, low C)

A refined subset of NOES. Vendors offer advanced coatings and low‑loss formulations for medium frequency.

• Pros:
• Lower loss and higher resistivity than low‑silicon steels
• Cons:
• Costs more than standard grades
• Use when:
• You run higher than 50/60 Hz but cannot justify cobalt or amorphous alloys

Cobalt‑Iron Alloys (e.g., 49% Co Fe) for High Saturation Flux Density

When torque density rules the day, cobalt alloys shine. They offer saturation up to ~2.35 T with good strength.

• Pros:
• Highest saturation among common soft magnetic alloys
• Strong at elevated temperatures
• Cons:
• Significantly higher cost, limited suppliers
• Higher hysteresis loss than NOES at low frequencies
• Use when:
• Aerospace, high‑speed rotors, compact traction drives must hit aggressive torque density under thermal limits

Nickel‑Iron Alloys (e.g., 80% Ni Permalloy, 50% Ni alloys)

Great for low‑frequency applications that demand very low coercivity and high permeability.

• Pros:
• Extremely low hysteresis, very high initial permeability
• Cons:
• Costly, lower saturation flux density than steels
• Use when:
• Low‑frequency precision devices and sensors, not mainstream traction motors

Amorphous and Nanocrystalline Alloys

Engineered for very low core loss at high frequencies due to ultra‑thin ribbon and lack of crystal grain boundaries.

• Pros:
• Very low eddy current and hysteresis losses at high frequency
• Cons:
• Challenging to process, brittle ribbon, limited shapes and stack methods
• Higher material cost and constraints on geometry
• Use when:
• High‑frequency motors or magnetic components benefit from ultra‑low loss more than they suffer from form‑factor constraints

Coatings and Insulation Classes

Insulation coatings control interlaminar resistance and durability. Vendors rate coatings for dielectric strength, cure temperature, and punchability. Organic coatings can offer excellent punchability. Inorganic or hybrid coatings tolerate higher temperatures. Specify coating class by performance requirement not brand name. Ask for dielectric breakdown voltage, maximum cure temperature, and friction coefficient where blank holder forces are critical.

Manufacturing & Assembly: Stamping, Laser Cutting, Bonding, Interlock, Welding

Material choice sets the ceiling. Manufacturing determines how close you get to it. You have several viable paths.

Blanking Methods

• Progressive‑die stamping
• Pros: Lowest cost per part at volume, tight repeatable tolerances, high throughput
• Cons: High tooling cost and lead time, burr formation if tooling dulls, residual stresses can raise loss unless steel and coating are optimized
• Best for: High‑volume production with stable geometry

• Laser cutting
• Pros: No tooling, fast iteration, complex shapes, good for prototypes and low volume
• Cons: Heat‑affected zone (HAZ) at the cut edge can increase local loss and reduce permeability, may require edge conditioning or stress relief
• Best for: Prototypes, bridge to production, frequent design changes

• Wire EDM
• Pros: Excellent edge quality with minimal HAZ, precise tight tolerance features
• Cons: Slow and expensive per part, limited volume throughput
• Best for: Small runs of high‑precision parts and tooling masters

• Waterjet
• Pros: No HAZ, reasonable speed, flexible
• Cons: Taper, edge roughness, potential delamination of coatings
• Best for: Some prototypes where HAZ must be avoided and edge quality is secondary

A quick way to align teams is to start with a shared definition of the components. Many organizations reference a general overview of motor core laminations to ensure mechanical and magnetic considerations stay in sync.

Stress Relief and Annealing

Cutting induces residual stresses that change magnetic properties. Post‑process annealing can restore permeability and lower core loss in many alloys. The anneal schedule depends on alloy, coating, and geometry. Confirm with the steel supplier and your lamination partner. If you plan to anneal after stacking, verify adhesive or bonding systems tolerate the thermal cycle.

Assembly Methods

• Interlocking tabs
• Tabs swage into matching features layer to layer. Think LEGO bricks snapping together.
• Pros: Fast, no adhesives or welds, strong mechanical bond
• Cons: Creates local mechanical deformation which can raise loss, can reduce stacking factor, airflow paths may open if not controlled
• Use for: Automotive scale where cycle time matters and loss impact is small relative to overall design

• Rivets and cleats
• Pros: Simple, low equipment cost
• Cons: Local shorting risk if holes and fasteners bridge laminations without insulation, reduced stacking factor
• Use for: Prototypes and low‑volume where simplicity beats automation

• Welding
• Pros: Robust joints, easy fixturing
• Cons: Creates conductive bridges across laminations, can short out layers and increase eddy losses, introduces HAZ
• Use for: Structural needs when you can tolerate some loss increase or when welds are outside the active magnetic path

• Bonding/Backlack adhesives
• Pros: Excellent interlaminar insulation, high stacking factor, silent stacks with lower vibration, good for high‑speed rotors
• Cons: Requires cure cycle and process control, adhesive adds cost, rework is limited
• Use for: High‑efficiency motors and high‑speed machines where vibration and loss must be minimized

• VPI (Vacuum Pressure Impregnation)
• Pros: Increases mechanical integrity, improves heat transfer, quiets the machine
• Cons: Adds process steps and cure time
• Use for: Stator stacks and wound cores that need rigidity and better thermal paths

Coating Integrity and Edge Quality

Burrs can short laminations. Excessive burr height wastes radial space and reduces stacking factor. Specify maximum burr height measured per industry practice. Call out deburring or brush grinding if your process tends to raise burrs. Protect the coating during handling since scratches can create local short circuits and hotspots.

Tolerances and Fit

You don’t want the stack to distort when pressed into a housing. Specify ID/OD roundness, tooth width tolerances, and key feature runout that reflect the actual magnetic path sensitivity. Coordinate with winding fill factors and insulation systems. The fit between rotor and shaft demands its own care. If you’re sourcing rotors as well, review core loss, balance grade, and any sleeve or containment method for high‑speed operation. For more on the moving half of the machine, many teams reference an overview of rotor core lamination alongside the stator design.

Best Fit by Application: Industrial Induction, BLDC/PMSM, High‑Speed Aerospace, Transformers

It’s easier to decide when you map choices to real applications. Below are typical best‑fit patterns and the pitfalls to watch.

Industrial Induction Motors (50/60 Hz, VFD duty up to a few hundred Hz)

• Material: NOES like M27 or M19 in 0.35–0.27 mm for line frequency. Drop to 0.25–0.20 mm for VFDs that run high electrical frequency.
• Process: Progressive stamping for volume. Laser for prototypes. Consider anneal if loss testing shows edge damage effect.
• Assembly: Interlock or bonding depending on noise and loss targets. VPI for stators.
• Watch out for:
• VFD harmonics that raise effective frequency and core loss
• Coating breakdown after stress relief if cure temperature mismatches

BLDC/PMSM for Appliances, Tools, HVAC, and E‑bikes

• Material: NOES with thin gauges for higher electrical frequency. Explore advanced low‑loss NOES if the duty cycle sees lots of high RPM.
• Process: Stamping for volume. Use laser early to iterate tooth shaping and slot geometry without committing to tooling.
• Assembly: Bonded stators are quiet and efficient. For rotors, secure magnet retention and consider sleeves for high RPM.
• Watch out for:
• Local saturation near tooth tips that adds hysteresis and field distortion
• Skew effects and slot/pole combinations that change local frequency content

If you’re deep in BLDC work, a refresher on the stator building block helps align mechanical and magnetic trade‑offs. See an overview of a typical bldc stator core to frame discussions with your manufacturing partner.

High‑Speed Aerospace or Turbo‑Machinery‑Class Motors

• Material: Cobalt‑iron for high saturation and elevated temperature strength. Use thin gauges to control loss.
• Process: Precision stamping or EDM depending on geometry. Plan an anneal to recover magnetic properties after cutting.
• Assembly: Bonded stacks with careful balance and tight runout control. Rotor containment sleeves and robust overspeed validation.
• Watch out for:
• Burst margins and rotor containment, not just loss
• Adhesive thermal stability and aging under vibration

EV Traction and Mild Hybrid Motors

• Material: Low‑loss NOES in thin gauges or cobalt‑iron in extreme power density cases. Evaluate segmented stators to reduce circumferential eddy currents in the yoke under inverter PWM.
• Process: High‑precision stamping with die monitoring and frequent tool maintenance. Quality control on burr height is critical.
• Assembly: Bonded stacks reduce NVH and improve thermal paths. Skew or step‑skew to manage cogging and acoustic tones.
• Watch out for:
• PWM switching frequencies and harmonics that push loss up
• Hot spot management due to local saturation near tooth tips and bridges

Transformer Cores

Motors prefer non‑oriented steels because flux rotates. Transformers often see uniaxial flux. Grain‑oriented steel dominates there.

• Material: Grain‑oriented electrical steel for low loss along the rolling direction. Amorphous or nanocrystalline cores for very high efficiency at higher frequencies.
• Process: Shearing, step‑lap stacking to reduce joint losses
• Assembly: Clamped or bonded stacks to control vibration and acoustic noise
• Watch out for:
• Joint design which can dominate total loss in small transformers

If transformers are on your scope, a quick overview of a typical transformer lamination core is a useful primer for your team.

Cost, Quality, and Supply Chain: Tooling, Coatings, Tolerances, and Testing

Let’s talk money and risk. You want to hit performance targets and keep unit cost predictable.

• Tooling vs flexibility
• Progressive dies slash per‑part cost at volume. They require capital and lead time. Laser keeps you nimble during early design. Many teams laser cut through EVT/DVT then move to stamping for PVT/production.
• Yield and burr control
• Dull tooling raises burrs and scrap. Poor fixturing damages coatings. Agree up front on burr height limits, inspection frequency, and corrective actions.
• Coating compatibility
• Coatings must survive your assembly process and any stress relief anneal. Review cure temperatures, punchability, and dielectric breakdown targets with your supplier.
• Stacking factor transparency
• Measure it on production stacks and feed the number back into your electromagnetic model. Design margins shrink when models match reality.
• Qualification and traceability
• Reference IEC 60404 measurement methods for magnetic properties. For motor efficiency validation, use IEEE Std 112 methods. Build a small plan: single‑sheet tester results from the steel vendor, ring specimen tests after cutting, and full‑stack loss on a dynamometer if practical.

Supply chain sanity check:

• Dual source materials when possible. Lock primary and secondary grades that meet your loss and Bsat targets.
• Request mill certs that include chemistry and typical magnetic properties. Track heat numbers and coil IDs for traceability.
• Align MOQ and forecast with coil widths and your lamination nest to control scrap.

Specification Checklist and Data‑Driven Selection

You can spend weeks in meetings debating materials and processes. Or you can answer these questions and let the choice emerge.

• Electrical frequency range and duty cycle
• Peak flux density targets in teeth and yoke
• Ambient and winding temperature limits

• Efficiency target at defined load points
• Torque density or size limit
• Acoustic and vibration constraints

• Candidate grade list with target thicknesses
• Required Bsat minimum at temperature
• Maximum core loss at specific B‑f points per IEC 60404
• Coating type with dielectric breakdown target and max cure temp

• Cutting process for proto and production
• Burr height limit, edge quality plan
• Stress relief anneal required or not

• Stack method: interlock, bonding, welds, rivets
• Stacking factor target and measurement method
• VPI or resin impregnation plan

• Material certs and incoming inspection
• Test coupons after cutting to measure loss and permeability
• Prototype motor efficiency per IEEE Std 112

• Annual volume, ramp, and EAU bands
• Tooling budget and amortization plan
• Alternate materials and emergency substitutes

Capture those answers in a one‑page spec. Hand it to suppliers with a request for data at your B‑f points. Ask them to cut sample laminations with the intended process, then measure core loss on a ring specimen. You’ll see which option wins without guesswork.

For the stator in particular, the geometry drives most of your electromagnetic performance and manufacturability constraints. If your organization needs a shared reference to align cross‑functional teams, point them to a concise overview of stator core lamination. It frames the conversation around slot shape, tooth tip design, stack height, and insulation.

Practical Case Snapshots

Let’s make it concrete with three short, real‑world style scenarios.

Case 1: 5 hp Industrial Induction Motor on 60 Hz with VFD

• Problem: The team needs IE3 efficiency. The drive runs up to 150 Hz electrical at high speed.
• Approach:
• Material: Switch from 0.35 mm M27 to 0.27 mm low‑loss NOES to curb eddy loss at higher frequency.
• Process: Progressive die stamping for production. Tighten burr height to less than 10% of thickness.
• Assembly: Interlock the stator stack. Add VPI to tame noise and improve thermal contact.
• Verification: Vendor provides IEC 60404 loss data at 1.5 T and 60/120/180 Hz. Team validates with ring specimens from stamped blanks.
• Result: Core loss drops 18% at 120 Hz. The motor meets IE3 without a frame size increase.

Case 2: 12,000 rpm Aerospace Starter‑Generator

• Problem: High torque density with a tight thermal envelope. Overspeed safety is critical.
• Approach:
• Material: 0.20 mm cobalt‑iron alloy for high saturation and temperature performance.
• Process: Precision stamping with post‑stack anneal per material spec. Edge conditioning to reduce micro‑cracks.
• Assembly: Bonded stator stack. Rotor with containment sleeve. Balance to a strict grade and validate burst margins.
• Verification: Loss mapping across the speed envelope. Temperature rise test in a pressure‑controlled chamber.
• Result: The design meets torque density and thermal rise. The safety review clears the rotor at 1.3× overspeed.

Case 3: High‑RPM BLDC E‑bike Motor

• Problem: The motor screams at high speed. Efficiency sags on long climbs.
• Approach:
• Material: 0.23 mm low‑loss NOES to cut eddy losses. Reduce local saturation at tooth tips with a slight tip radius change.
• Process: Laser cut prototypes to iterate quickly. Move to stamping once geometry locks.
• Assembly: Bonded stator for lower acoustic noise. Optimize skew to reduce cogging.
• Verification: Back‑to‑back efficiency test at cruising and climb speeds. Microphone array for acoustic tones.
• Result: Efficiency improves 2–3 percentage points. Acoustic peaks drop several dB in the 2–3 kHz band.

Common Traps and How to Avoid Them

• Chasing thickness without checking stacking factor
• Thinner laminations reduce eddy loss. If coating and burrs lower stacking factor too much, you give back torque density and efficiency. Measure stack factor on real parts.
• Specifying a famous grade without proper data
• Material labels like “M19” vary by mill and coating. Ask for loss vs B‑f curves and Bsat at temperature. Data beats labels.
• Ignoring cutting effects
• Laser makes design iteration easy. The HAZ can inflate loss. Test with the intended process before you lock performance expectations.
• Over‑relying on simple lamination loss models
• The Steinmetz equations and their variants give trends not guarantees. Validate with measurements through your actual process.
• Missing the inverter’s fingerprints
• PWM and harmonic content change your effective frequency and flux waveform. Model and test with realistic drive waveforms.

How Procurement Can De‑Risk the Buy

Procurement sits at the center of cost, quality, and delivery risk. Here’s how to hedge without slowing the program.

• Ask for a process FMEA that covers cutting, deburring, stacking, and coating integrity
• Lock a PPAP level that matches your risk tolerance and criticality
• Require traceable material certs and coil IDs on each lot
• Set inspection points for burr height, stack height, and dielectric integrity
• Build a second source for both steel and lamination manufacturing if volume and risk justify the effort

One more tip. Share real usage data with the supplier. Tell them your duty cycle, max temperature, and drive type. Good partners optimize more than price when they understand your constraints.

Frequently Asked “Should I…” Questions

• Should I always use the thinnest gauge available
• Not always. Thinner gauges cut eddy loss but reduce stacking factor and raise cost. You want the thinnest gauge that meets your loss targets within budget.
• Should I anneal after stamping
• It depends on material and measured impact of cutting. If ring specimen tests show elevated loss after stamping, annealing can recover properties. Validate with your alloy and coating.
• Should I bond or interlock
• Bonding lowers loss and noise at the cost of process complexity. Interlocking wins on speed and cost. Pick based on efficiency and NVH targets.
• Should I pick cobalt for torque density
• Only if you truly need the higher saturation and temperature strength. Cost rises sharply. Low‑loss NOES with clever geometry often hits targets for less.

Engineering Takeaway: What to Do Next

• Define operating frequency, Bsat targets, and efficiency points before you pick materials.
• Shortlist two to three lamination materials with thickness options. Ask for IEC 60404 loss data at your B‑f points.
• Cut and test with the intended manufacturing process. Use ring specimens or Epstein frames to measure core loss after cutting.
• Specify coating performance, stacking factor target, and burr height limits in the drawing. Verify them in first articles.
• Choose assembly based on efficiency and NVH goals. Bond for premium efficiency and quiet. Interlock for speed and cost.
• Validate motor efficiency using IEEE Std 112 methods. Close the loop between model and measurement.

If you need to brief a mixed team quickly, start with a shared overview of stator core lamination for the stationary side, then pair it with rotor core lamination for the rotating side. For a broader introduction to lamination families and material options, this primer on electrical steel laminations helps align vocabulary. When you reach material trade‑offs, especially for 50/60 Hz through medium frequency machines, an overview of silicon steel laminations keeps the conversation focused on real, available alloys. And if your project involves BLDC motors, you can share a concise view of the typical bldc stator core so mechanical, magnetic, and manufacturing stakeholders stay on the same page.

You’ve got this. Make a data‑driven choice, validate with process‑realistic tests, and you’ll ship a motor that runs cooler, quieter, and longer.

References and Standards

• IEC 60404 series, Magnetic materials — Methods of measurement and material specifications
• IEEE Std 112, Standard Test Procedure for Polyphase Induction Motors and Generators
• Vendor datasheets for NOES, cobalt‑iron, and amorphous alloys with loss vs B‑f curves and coating specifications

Note: Always verify specific grade properties and coating performance with the steel mill or lamination supplier since formulations and processes vary by source and region.