Optical Reconstruction and Quantitative Evaluation of Arc Position in Stud Welding

This study presents an optical reconstruction method for the quantitative evaluation of arc position in stud welding. Knowledge of the instantaneous arc position is essential for understanding arc dynamics and enabling process monitoring and control. The relative spatial position of the arc is determined from the geometric centroid of an intensity distribution recorded by eight directionally arranged photodiodes. Calculated using area-weighted polygon decomposition, the centroid provides a consistent two-dimensional representation of arc motion and enables the derivation of angular and amplitude-related quantities. The method is not intended to deliver absolute metric arc positions but to provide a reliable relative description of arc movement. Whereas laser-based stereoscopic systems require an additional illumination arrangement and high-speed camera systems rely on the acquisition and processing of image sequences, the proposed method evaluates photodiode signals acquired directly within the welding hardware. This enables a compact, process-integrated implementation suitable for real-time arc monitoring. The proposed reconstruction method is evaluated under conventional direct-current, magnetically influenced direct-current, and alternating-current welding conditions. Validation against stereoscopic high-speed camera measurements showed good agreement in trajectory shape and dynamic behaviour, with mean Pearson correlation coefficients above 0.97 and a mean Euclidean deviation of 0.59 mm, corresponding to 10.4%, for rotational arc motion. The approach thus enables reliable analysis of arc movement and spatial energy distribution over the entire welding duration. Overall, the proposed methodology provides a robust and efficient tool for quantitative arc motion analysis in stud welding.