Studying the quality of laser welding process using time-frequency distributions with rotated kernel

Laser welding is becoming more and more important in automotive industry and quality of the weld is critical for a successful application. In many cases the increase in welding speed provided by laser welding has caused the welding system operator to be unable to keep up with the production rate while inspecting each part. Therefore, real time on-line inspection of the weld must be provided. To address this need, in the last years a number of on-line inspection systems, have being developed to improve weld quality and reduce overall costs. The weakness of these systems is however represented by the poor signal analysis methods, adopted to get information about the condition of the weld. In this paper we explore the time-frequency distributions with rotated kernel, to extract information from signals detected during the laser welding process. The proposed method yields significantly improved components localization. We briefly recall the fundamental concepts of the theory of time-frequency representations, after that we describe the rotation of the kernel through the fractional Fourier transform. Finally we compare the proposed time-frequency distributions by analyzing signals detected during the laser welding, demonstrating the advantages of the proposed method, giving practical applicability to the proposed method.