Process zone morphology and melt dynamics in laser remote fusion cutting (RFC) revealed by high-speed X-ray imaging

Laser material processing procedures yield numerous benefits, as non-contact manipulation of the workpiece, high precision, and extensive automation capabilities. For metal joining, laser beam welding is a widely used process employed in industry, for example in automotive body construction and in the production of electronic components. With the same optical setups as usually used for laser beam welding, a melt ejection can be induced in sheet metal, resulting in the formation of a cut. This enables laser remote fusion cutting (RFC) based on a melt ejection without the need for tools near the process zone. A comprehensive understanding of the conditions and mechanisms causing the melt ejection or preventing it is yet to be achieved. In this study, in-situ observations of the process zone in RFC were performed using high-speed X-ray imaging with synchrotron radiation, achieving frame rates up to for steel samples and for AlMg3 samples. Key features of the process zone morphology are extracted by means of image processing from the recordings, such as the angle of front wall inclination or the ejection direction for different process parameters. The front wall angle for RFC is in line with an established model for the front wall angle in laser beam welding. Propagation-based phase-contrast imaging reveals the melt film at the cutting front, showing a decrease of the melt film thickness with increasing feed velocities. Melt dynamics at transitions between process states of cutting and not cutting could be observed. The temporal resolution was insufficient to capture humps in the melt film at the front wall in steel samples. These were resolved for AlMg3 samples, confirming that humps at the front wall play an important role in the melt dynamics. • Synchrotron radiation enables high-speed X-ray imaging of the process zone. • Propagation-based phase-contrast imaging reveals the melt film at the cutting front. • The melt film thickness decreases with increasing feed velocities. • For high processing velocities melt is ejected via the side walls of the process zone. • Movement of humps at front wall is visible at high framerates for AlMg3 sample.