Depth measurement performance of OCT during laser welding with single-mode core and ring beam configurations

The demand for precise measurements of high-speed laser welding depth is increasing due to growing e-mobility applications. Optical coherence tomography (OCT) can measure keyhole depth in real time. Newer fiber laser generations, ideal for such applications, allow single-mode core/ring configurations. However, OCT’s usability with small keyhole apertures may cause measurement inconsistencies. This work proposes a systematic analysis of signal behaviour using a contemporary fiber laser with a single-mode core and a ring with separate power control, producing focal core and ring sizes of 40 µm and 285 µm, respectively. Bead-on-plate experiments were conducted on 5 mm thick EN AW-1050 Al-alloy. Core and ring power levels were systematically analysed along with scan speeds. The OCT focal beam of 35 µm was aligned with the laser beam for different process parameters. Keyhole depth was compared to molten seam depth from metallographic cross-sections. Alignment protocols were showcased to highlight the sensitivity of OCT measurements.