Ivestigating the weld depth behaviour using different observation techniques: X-ray, inline coherent imageing and highspeed observation during welding ice

Abstract

For a comprehensive understanding of the deep-penetration laser-welding process, it is of fundamental interest to understand the dynamic behavior of the capillary. The X-ray system of the Institut fuer Strahlwerkzeuge (IFSW) allows to record a two-dimensional projection of the capillary with frame rates up to 10 kHz.Hence the system is capable to gain information about the welding capillary, such as size and shape. However, the laser-welding process is a highly dynamic process with significant changes in time periods shorter than 0.1 ms.Queen’s University and Laser Depth Dynamics (LDD) have developed a sensor based on inline coherent imaging [1] which provides direct geometrical measurements of the keyhole depth and associated dynamics at rates >300 kHz with micron-scale precision. The technique is based on spectral domain low-coherence interferometry and is delivered through a camera port and combined co-axially with the process beam.The two measurement methods were set up in a combined experiment.The X-ray system recorded the shape and depth of the capillary with a spatial resolution of about 100 µm and a frame rate of 1 kHz, whereas the depth sensor from LDD provided 200 kHz at a single spot with axial resolution on the order of 10 µm.The present contribution compares the results of the two methods for steel and aluminum welds allowing new insights to the short-timescale behavior of the capillary.In order to understand the principal findings, the results were compared with high speed videos, taken during welding of the transparent material ice. Compared to the X-ray technique, a higher spatial resolution can be obtained at high repetition rates.At a first glance, it might be astonishing, that welding of ice can be compared with welding of metals. In a large number of experiments, however, we found that during welding of ice a lot of phenomena known from welding of metals (especially steel and aluminum) are also present during welding of ice, but can be observed much more clearly because of the low temperature and the transparency of the material.For a comprehensive understanding of the deep-penetration laser-welding process, it is of fundamental interest to understand the dynamic behavior of the capillary. The X-ray system of the Institut fuer Strahlwerkzeuge (IFSW) allows to record a two-dimensional projection of the capillary with frame rates up to 10 kHz.Hence the system is capable to gain information about the welding capillary, such as size and shape. However, the laser-welding process is a highly dynamic process with significant changes in time periods shorter than 0.1 ms.Queen’s University and Laser Depth Dynamics (LDD) have developed a sensor based on inline coherent imaging [1] which provides direct geometrical measurements of the keyhole depth and associated dynamics at rates >300 kHz with micron-scale precision. The technique is based on spectral domain low-coherence interferometry and is delivered through a camera port and combined co-axially with the process beam.The two measurement methods were set up in a combined experiment.The X-...