AkuProLas: Acoustic inline process monitoring for laser welding applications

The process of laser welding plays an increasingly important role in industrial production environments, in particular - but not only - the automotive sector. Despite its growing importance, the possibilities for both a reliable and robust process monitoring and quality control are still sparse; almost every modern in-process monitoring approach is based on electromagnetic techniques. All investigations of acoustic emissions were concentrated on lower frequency ranges(< 100 kHz air-borne acoustic emissions (ABAE/LSE), < 500 kHz structure-borne acoustic emissions (SBAE/KSE)). In order to set up a welding process with new parameters, metallography is applied offline to measure all important quality parameters of the laser welds. The project "AkuProLas", presented in this paper, aims at facilitating the higher-frequency acoustic emissions (ABAE: 700 - 1200 kHz, SBAE: 400 -1000 kHz) of the process to enable a 100 percent in-process quality control. The concentration on high frequencies combined with an in-process frequency analysis primarily allows a much better rejection of contaminating environmental noise, dramatically enhancing the signal-to-noise-ratio (SNR) between flawless processes and welding defects. In the combination of SBAE and ABAE, we show that in particular the penetration depth correlates perfectly with SBAE, whereas the influence of eventual coatings of the welded parts can be characterized by ABAE. We validate this with conventional metallographic investigations and also give an outlook on industry-ready monitoring concepts using the results of this project.