Weld seam position sensing of laser stake welded T-joints using plasma voltage signals

Laser stake welding of hidden T-joints requires precise lateral beam positioning relative to the concealed web sheet. Existing monitoring approaches based on optical coherence tomography, camera vision with neural networks, or spectroscopy involve substantial hardware costs, extensive training data, or limited temporal resolution. This study presents a plasma voltage sensing approach using a voltage divider circuit with an external copper electrode. Experiments on S355 steel demonstrate that electrode positioning critically determines measurement capability. A leading electrode configuration yields clearly separated voltage distributions for weld-in (μ = 0.988 V) and weld-through (μ = 0.169 V) conditions, enabling threshold-based classification. The sensor offers a cost-effective alternative to established monitoring technologies for industrial beam positioning control.