Electric motors drive our world forward, but hidden behind their efficiency is a subtle factor few talk about: lamination punching.
Why Punching Matters in Motor Design
Most Permanent Magnet Synchronous Machines (PMSMs) are built from laminations — thin sheets of electrical steel stacked together. To manufacture these laminations, industries often use punching, a mechanical process that cuts the steel into shape.
Punching might seem like a routine step, but it introduces tiny stresses at the cut edges of the material. These stresses can degrade the steel’s magnetic properties, potentially leading to increased losses, lower efficiency, and more noise and vibration in the motor.
Our Study: Digging Deeper into Punching Effects
In this study, we used advanced finite element modeling (Altair Flux and OptiStruct) to study how punching impacts both electromagnetic performance and NVH (Noise, Vibration, Harshness) of a widely studied benchmark motor — the Toyota Prius 2004 interior PMSM.
We compared two models:
- One with ideal laminations (no punching effect).
- One with realistic punched laminations (including stress effects).
Observations
- Minimal impact on some parameters
- Back-EMF, cogging torque, and power factor were largely unaffected by punching.
- Significant effect on losses
- Iron losses increased with speed, leading to about 1% drop in efficiency at high RPM.
- This is directly linked to degraded magnetic performance at the edges of punched steel sheets.
- Torque ripple sensitivity
- Up to 5% variation was observed, which can influence drive smoothness.
- Surprising NVH results
- Contrary to expectations, noise levels slightly decreased (about 1.1 dB lower Equivalent Radiated Power) with punching.
- This shows that punching can have complex, sometimes counterintuitive, effects.
Why This Matters
For EV manufacturers and motor designers, these insights are critical. A 1% efficiency loss may sound small, but across a fleet of vehicles, it translates into significant energy consumption and range impact. Similarly, torque ripple affects driving comfort, and NVH is directly tied to customer perception of quality.
By accounting for punching effects early in the design stage, engineers can:
- More accurately predict real-world performance.
- Optimize lamination geometry and materials.
- Develop strategies to balance efficiency, NVH, and cost.
Looking Ahead
This study reinforces the importance of bridging manufacturing effects with electromagnetic and acoustic simulations. As we push for higher-performance, quieter, and more efficient electric machines, seemingly small details like punching will play a bigger role in next-generation motor design.
For a detailed discussion, figures, and methodology, you can read the full IEEE paper here:
Impact of Lamination Punching on Electromagnetic Performances & NVH Behavior of PMSM: A Comprehensive Study
