Using sound to make better electric motors

Electric vehicle sales are rising, and automotive companies must keep up with fast, precise, reliable, and cost-effective manufacturing. Welding together the hundreds of compact, rectangular copper wires used in high-performance motors is one of the largest manufacturing challenges. But while laser welding is fast and highly automated, existing quality-control methods such as X-ray scans and physical sensors either interrupt production or cannot catch hidden defects at industrial speed.

Baader et al. developed a method of quality-checking laser-welded copper wires using sound. By integrating an optical microphone into the production process, they could reliably identify bad welds without touching the parts.

“Every time an electric motor is scrapped because of a bad weld, hundreds of good welds are scrapped along with it. That’s expensive and environmentally wasteful,” said author Marcel Baader. “We wanted a way to catch defects the moment they happen — like a smoke alarm for the welding process.”

The researchers combined a laser welder with an optical microphone, then intentionally produced poor, medium, and good-quality welds. They scanned each weld with 3D X-ray tomography to see any internal defects, then matched them with their corresponding audio recording to search for patterns.

The team found several “sound fingerprints” that correlated with trapped gas bubbles, indicating weakened welds. Next, the team hopes to use machine learning to develop real-time quality predictions that trigger automated corrections during production.

“This is a real step toward inline, non-contact quality inspection for the mass production of electric motors,” said Baader. “If every weld can be checked in real time, faulty welds can be caught immediately instead of being discovered later — saving materials, energy, and cost.”

Source: “Quality monitoring in laser welding of rectangular copper wires for traction drives using an optical microphone,” by Marcel Baader, Fabian Giesbert, Tim Raffin, Jörg Franke, and Florian Risch, Journal of Laser Applications (2026). The article can be accessed at https://doi.org/10.2351/7.0001989 .

This paper is part of the Proceedings of the International Congress of Applications of Lasers & Electro-Optics (ICALEO 2025), learn more here .