Introduction – A New Era of Motor Core Design Freedom

Self-bonding laminations (Backlack) transform motor-core design by bonding each sheet under heat and pressure to create a rigid, fully insulated stack. Instead of stitching metal together with rivets, interlocks, or weld beads, the adhesive layer unites the laminations across their full surface—no holes, tabs, or heat-affected zones.

That simple shift removes long-standing mechanical constraints and hands designers new freedom over tooth tips, slot openings, skew, and stack length. With geometry no longer dictated by fastening points, it becomes easier to prioritize electromagnetic performance first and packaging second. With self-bonding laminations, the result is a path toward more compact machines with cleaner flux paths, higher usable stacking factor, and quieter operation—cores that are easier to tailor to the envelope and duty cycle of EVs, robotics, and medical devices built for demanding, high-efficiency work.

The Old Constraints of Traditional Lamination Assembly

Before self-bonding laminations, motor cores were held together by interlocking tabs or welding beads—methods that get the job done but quietly tax the design. Interlocking forces you to reserve space for tabs and bridges, loosening stack height tolerance as slight localized deformations accumulate through the stack.

Welding introduces heat-affected zones and residual stress, which can distort the outer diameter of the stator core and complicate creating potential shorting-paths. Both methods also carve away active material area: holes, small riveting notches, and bead paths occupy space that could have carried flux. The result is geometry defined by the joining scheme— conservative tooth shapes, limited skew angles etc.

By contrast, self-bonding laminations remove the fastener footprint and the thermal side effects, so designers can hold tighter stacking factor and tolerances, shape tooth tips for the field, and reclaim eSteel for its pristine electromagnetic performance—leading to more compact, efficient, quiet and custom-tailored electric machines built around performance rather than constraints.

How Self-Bonding Works at the Material Level

Backlack—the coating behind self-bonding laminations—is a heat-activatable adhesive applied to electrical steel at the manufacturing stage from the electrical steel manufacturers. Each sheet receives a uniform, thin layer that doubles as interlaminar insulation.

During manufacturing assembly, laminations are stacked to net height, then press-cured: pressure and controlled heat briefly soften the coating so it wets the adjacent surface; on cooling, the film re-solidifies and locks the stamped lamination sheets as one. No interlocking tabs or weld beads(paths)—so no holes to punch and no heat-affected zones. Because the bond forms across the full surface, load is spread evenly.

The insulation remains continuous from tooth tip to back iron(yoke), and the base material’s grain structure is left untouched by joining operations. In practice, self-bonding laminations deliver a core that is rigid, well-insulated, and dimensionally consistent—an ideal foundation for tight skew control, precise winding, and higher stacking factor.

Impacts on Iron Core Loss values

By removing interlock bridges and weld beads, self-bonding laminations change how loss is generated in the core. Without interlocking points, the lamination stack avoids metal-to-metal shortcuts that encourage circumferential eddy-current loops; the continuous insulating bond keeps current paths broken and localized.

Likewise, eliminating welding prevents heat-affected zones and residual stress that would otherwise widen the B–H loop, so both eddy-current and hysteresis components drop.

In our internal testing on a 200 mm OD stator core built to identical geometry, frequency-swept from 50 to 400 Hz, the stack assembled with self-bonding laminations delivered roughly 30% lower total core loss than the interlocked version. While results will vary with eSteel grade, thickness, and cure parameters, the direction is clear: remove mechanical bonding method, preserve insulation, and let the electromagnetic design work as intended—yielding more compact, efficient, and custom-tailored machines.

Implications for High-Performance Applications

Across high-performance sectors, the gains from self-bonding laminations show up where it matters most. In EV traction motors, lower iron core loss and the absence of weld-induced hot spots translate into better energy efficiency; designers can chase longer range or smaller battery packs without sacrificing torque density.

For robotics—especially frameless torque motors embedded in joints—stack integrity without interlock tabs frees tooth and slot geometry, helping you fit high-torque profiles into tight envelopes while maintaining smooth, low-cogging motion.

In medical devices, fewer mechanical discontinuities and a fully bonded stack help reduce vibration and audible noise, supporting miniaturization and a calmer acoustic signature. Because the mechanical bonding scheme no longer disturbs the geometry and insulation, motor design engineers can prioritize electromagnetic performance, thermal behavior, and packaging simultaneously.

In short, the design freedom enabled by self-bonding laminations turns into market-facing benefits: more efficient e-mobility, compact robotic joints, and quieter medical systems that serve users and brands alike.