Holistic sensor concept for process control and quality assurance in laser beam welding based on Optical Coherence Tomography

Optical Coherence Tomography (OCT) enables the acquisition of direct information about the geometry of the process zone during laser beam welding. The measuring principle allows for spatial and temporal highly accurate measurements that are hardly affected by process emissions or metal vapor/plasma. A novel sensor concept based on OCT was evaluated for both multi-mode and single-mode laser radiation as well as for fixed and remote optics. The sensor was equipped to a 3D scanner unit allowing for measurements before, in, and after the process zone. Fundamental studies on aluminum, copper, and galvanized steel were carried out to analyze the effect of the material, the process, and the measurement parameters. Scan lines before and after the process zone were applied for tracking edges and assessing the weld seam topography during the process in real-time. Measurements coaxial to the laser beam revealed the capillary depth for spot sizes down to 50 µm.