Invisible spatter in LPBF: UCL team analyses spatter with X-ray camera

Laser Powder Bed Fusion (LPBF) is one of the key processes in metal 3D printing when it comes to complex geometries and high component quality. A recurring problem, however, is the formation of spatter: tiny particles that are ejected from the powder bed during the melting process, deposit on the surface or become embedded in subsequent layers, where they cause porosity and surface defects. For safety-critical applications in aerospace or energy systems, this can significantly complicate the certification of additively manufactured components. In addition, the particles often oxidize, which limits the reusability of the remaining powder.

A team from the UCL Department of Mechanical Engineering, led by Prof. Lee and Dr. Leung, has now investigated the formation mechanism of these spatter phenomena in detail. To this end, the researchers used a specially developed LPBF system, the Quad-laser in situ and operando process replicator (Quad-ISOPR). The system features four lasers, an industrial scan head from Renishaw and an argon process chamber that reproduces the process conditions of an industrial machine as closely as possible.

In cooperation with the European Synchrotron Radiation Facility, the setup was combined with high-speed X-ray imaging. With frame rates of up to 40,000 frames per second, the melt pool, vapor plume and particle trajectories could be observed almost in real time. The analysis showed that spatter is not only created by the direct ejection of molten droplets, but also by an interplay of metal vapor, gas flow and cascading powder. This leads to the formation of particle clusters that deposit on the component surface or initiate defects in deeper layers.

From this, the researchers identified two additional mechanisms of spatter formation and derived process strategies, such as adapted scan paths and optimized gas flow. For industrial LPBF users, the work opens up the possibility of linking process monitoring, simulation and parameter development more closely and systematically assessing the suitability of the process for critical components.

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