Robotics and Cobots: Precision Lamination Stacks for Servo Motors

When you watch a robot arm place a chip on a PCB or a cobot gently hand over a part to a human, you’re really watching a stack of very thin steel sheets doing their job perfectly.

Those sheets — the lamination stack inside the servo motor — quietly decide whether your robot feels silky and safe or jerky and noisy, whether your cobot joint runs cool for 10 years or cooks itself in three. Yet most discussions about robotics and cobots barely mention them at all.

This article is about treating lamination stacks as a first-class design lever in robotics and cobots, not a commodity you order at the end of the project.

• In the next sections, you’ll see:
  • How servo motors and lamination stacks translate directly into accuracy, safety, and “feel” in cobots
  • Which materials, thicknesses, and joining methods actually matter (and why)
  • How geometry tricks like skewed stacks and slotless designs tame cogging torque and noise
  • How to choose stack technologies differently for industrial robots vs cobots
  • A practical checklist you can use the next time you spec a lamination stack

1. Servo motors, robotics, and cobots: why laminations suddenly matter more

Servo motors are the muscle fibers of robotics: compact, high-torque, and constantly monitored by feedback sensors to hit precise positions and velocities. They close the loop with encoders or resolvers, comparing commanded position with actual position and correcting in real time, which is why they dominate in robots, CNC machines, and automation lines.

For industrial robots, the brief is usually simple: high torque density, speed, and uptime. Cobots, however, add extra constraints: backdrivability, low cogging, low acoustic noise, and inherent safety when bumped into by humans. Those “soft” attributes are deeply influenced by what’s happening inside the magnetic core — the lamination stack — not just by your control software.

• In both robots and cobots, the lamination stack influences:
  • Torque density and efficiency (how much torque you squeeze per kilogram)
  • Smoothness at low speed (cogging torque, torque ripple, and “feel”)
  • Thermal behavior and lifetime (core loss, hotspot distribution)
  • Noise and vibration (NVH) — especially critical around humans
  • Safety characteristics like backdrivability and compliant behavior in cobots

2. Inside the lamination stack: thin steel sheets, big consequences

Most high-performance servo motors still rely on electrical steel laminations: low-carbon iron alloyed with ~0.5–6.5% silicon, chosen for high permeability and low core loss. These sheets are usually 0.1–1.0 mm thick, punched or cut, then stacked with insulation between them to block eddy currents.

Thinner sheets mean lower eddy current loss at high switching frequencies — an increasingly big deal as servo drives push higher PWM frequencies and as robotic joints go to higher pole counts and speeds. At the same time, going thinner drives up cost and manufacturing complexity, which is why serious lamination suppliers obsess over stamping dies, burrs, and coatings.

Key lamination parameters for robot & cobot servo motors

• As a robot designer, think of lamination design as three coupled dials:
  • Material system – which grade of electrical steel (or alternative) you select
  • Geometry – tooth shape, slot/pole combination, skew, and stack height
  • Assembly quality – joining method, burr control, and alignment precision

3. Joining methods: how the stack is held together changes what the cobot “feels”

Those hundreds of thin sheets don’t magically stay together. They’re joined using methods such as adhesive bonding, self-bonding (Backlack), mechanical interlocking, riveting/bolting, cleating, and welding.

Research shows a constant tug-of-war: you need mechanical strength and manufacturability, but you don’t want to ruin magnetic performance by damaging insulation or introducing residual stresses and distortion. Glue-based joining tends to maintain low core loss and good insulation, while welding or aggressive mechanical interlocks can increase losses and noise if not carefully controlled.

Joining methods vs impact on servo lamination stacks

• For cobots in particular, bonded or self-bonded stacks are attractive because:
  • They reduce eddy current loss and thereby heat and drift
  • They damp vibrations and noise — critical when the robot works beside humans
  • They keep the torque constant more linear, simplifying force estimation and control

4. Geometry in the stack: fighting cogging, ripple, and noise

If your robot joint feels “notchy” when you backdrive it by hand, you’re feeling cogging torque — parasitic torque that comes from the interaction of permanent magnets with the stator teeth and laminations.

Designers fight this using a mix of electromagnetic design and lamination geometry: adjusting slot/pole combinations, altering magnet shape, changing tooth tip geometry, and skewing the lamination stack. A skewed rotor or stator slightly twists the laminations along the axis so that slotting harmonics “average out” along the stack length, significantly reducing cogging torque and torque ripple with only a small impact on torque constant and efficiency.

• For robotics and cobots, lamination-level geometry levers include:
  • Skewed rotor/stator stacks – reduce cogging, torque ripple, and acoustic noise, especially important for low-speed “creep” moves and cobots working near people
  • Slotless or toothless stator designs – using a ring-shaped laminated core with no teeth to almost eliminate cogging, helpful in high-end torque sensing joints
  • Optimized slot/pole combinations – fractional slot designs to break symmetry and spread harmonics
  • Tooth tip shaping and notching – local tweaks to reduce saturation and torque ripple at specific load ranges
  • Aperture and ID/OD ratios – especially in frameless motors where gearboxes or sensors live inside the rotor

5. Industrial robots vs cobots: different lamination priorities

An industrial welding robot throwing sparks in a fenced cell has a very different risk profile from a cobot assembling electronics next to a human operator. But inside both, lamination stacks still define the torque, smoothness, and thermal envelope you can work with.

For industrial robots, lamination design tends to prioritize torque density, efficiency, and cost, especially in large volumes. Slightly higher cogging torque can often be tolerated because a gearbox, stiff structure, and clever control loops can hide a lot.

For cobots and exoskeleton-style systems, backdrivability and low apparent impedance are key. High-torque-density joint motors are often paired with low gear ratios or quasi-direct-drive architectures; in that regime, every bit of cogging and friction is amplified into what a human physically feels.

• When you design lamination stacks, treat the two classes differently:
  • Industrial robot joints
    • Can live with interlocked or welded stacks if it cuts cost and boosts throughput
    • Aim for good but not perfect cogging performance; drives and gearboxes help mask imperfections
    • Thermal limits often set by duty cycle and ambient, not human comfort
  • Cobots and human-interactive robots
    • Favor bonded / self-bonded stacks and skewed laminations for ultra-smooth torque
    • Push for thinner laminations and better coatings to reduce loss and temperature drift
    • Care a lot about acoustic signature and tactile feel when backdriven

6. Manufacturing realities: how tolerances show up in robot behavior

On paper, a lamination stack is just a stack of perfect shapes. On the factory floor, details like burr height, coating robustness, and shaft fit give your motor its actual personality.

High-speed progressive stamping and rapid-stamping presses are the workhorses of lamination production, capable of millions of hits per die. Done right, they deliver tight tolerances and high stacking factors; done carelessly, they leave burrs that pierce insulation, increasing inter-laminar loss and audible noise. Many suppliers complement stamping with laser cutting, single-notching, and rotary notching for prototypes or large diameters, then assemble stacks via interlocking, bonding, or welding in-line.

On top of that, inspections — CMM checks, vision systems, iron-loss testers, and Franklin inter-laminar resistance tests — are critical to make sure your simulated motor is the motor you actually get.

• Manufacturing choices that strongly affect robot & cobot performance:
  • Burr control – lower burrs protect coatings and keep core loss and noise down
  • Coating selection & application – robust, uniform insulation maintains low loss and stable skew over the motor’s life
  • Stacking and joining process stability – consistent pressure, temperature, and alignment keep backdrivability and cogging behavior consistent across batches
  • Shaft-to-stack connection (e.g., precision-shape holes, press fits, inserts) – influences runout, vibration, and long-term reliability of joints

7. Beyond classic laminations: SMCs, axial-flux, and future robot joints

While stacked electrical steel is still dominant, there’s a growing push toward soft magnetic composites (SMCs) and axial-flux architectures in high-performance drives, including EVs and robotics. SMCs use insulated iron powder pressed into 3D forms, making it possible to design motors with truly three-dimensional flux paths and simplified assembly compared with traditional laminations.

For robotics and cobots, that opens doors to flatter, pancake-like joints, integrated cooling paths, and topologies that are hard or impossible with simple stacked sheets. However, SMCs bring their own trade-offs in terms of material cost, achievable flux densities, and process maturity, so many designs will continue to rely on carefully optimized lamination stacks for the foreseeable future.

• If you’re pushing the envelope, consider:
  • Hybrid cores – combining classic laminations in the active region with SMC or machined flux guides where 3D paths help
  • Axial-flux servo designs – enabled by carefully punched axial laminations or SMC cores, offering high torque density in a short axial length
  • Advanced coatings and amorphous alloys – to shave core losses further and keep joint temperatures low in tightly packaged arms

8. Practical checklist: designing your next robot or cobot lamination stack

At this point, it’s easy to feel overwhelmed — there are many knobs to turn. To keep it grounded, here’s a human-level design checklist you can walk through the next time you specify a lamination stack for a robotic joint.

• 1. Start from the interaction, not the datasheet.
  • Ask: What should this joint feel like when a human pushes it? That tells you how aggressive you must be on cogging torque, noise, and backdrivability.
• 2. Define your loss and temperature budget explicitly.
  • With your drive frequency and duty cycle, roughly budget core loss vs copper loss. Use that to decide lamination thickness and steel grade.
• 3. Choose a joining method that matches your “feel” targets.
  • Cobots and precision axes: lean towards self-bonded or glued stacks.
  • Heavy industrial joints: interlocking or welding may be acceptable if tested.
• 4. Decide early whether to skew.
  • Skew requires tooling choices and stacking process changes. Decide at the lamination specification stage, not after you’ve built the prototype.
• 5. Lock in manufacturable tolerances, not fantasy ones.
  • Work with your lamination supplier to match die capability, burr limits, and coating systems to your performance model.
• 6. Prototype with the real joining & stacking process.
  • A laser-cut, bolted prototype behaves differently from a production interlocked or bonded stack. Validate with something close to the final process.
• 7. Measure what humans will feel.
  • Don’t just measure efficiency; plot cogging torque, torque ripple, backdrive torque, and acoustic spectra. That’s what operators and end-users actually experience.

If you treat the lamination stack as a strategic component instead of a line item, your robots and cobots will move differently — smoother, quieter, more predictably, and more safely.

And the next time someone raves about how “natural” your cobot joint feels, you’ll know it started with a pile of very thin, very carefully joined pieces of steel.