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Additive manufacturing by means of laser powder bed fusion (LPBF) works by selectively fusing metal powder layer by layer using a laser beam. These powders must meet strict requirements in terms of particle size and shape. However, due to a lack of sufficient process control in regards to the powder production by way of two-fluid atomisation, this can often only be achieved by additionally utilising expensive sieving processes.

As part of the project "Metal Powder Production for Additive Manufacturing" (PPAM), funded by the Indo-German Science & Technology Centre (IGSTC), scientists from the Indian Institute of Science Bangalore, the Indian Institute of Technology Kharagpur, Tata Steel Ltd, the SMS group GmbH and the Technical University of Darmstadt are collaborating in order to develop a better understanding of close-coupled atomisation (CCA) and, ultimately, to contribute to optimising this process. This form of two-fluid atomisation is based on the interaction of a gravity-driven stream of liquid metal with a high-velocity gas flow. Here, the gas usually reaches supersonic velocity, which is why the flow field is characterised by effects of compressibility.

At the Institute for Fluid Mechanics and Aerodynamics (SLA), the focus within the joint project is on modelling the atomisation process. For this purpose, a model test rig is operated, which, based on a dimensional analysis, employs water and air as substitute fluids for the atomisation. Consequently, this allows for improved accessibility for modern optical measurement systems. In particular, the phase Doppler measurement technique enables the accurate determination of particle size and velocity distributions in spite of the extreme process conditions.