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SMOB - Research project

In situ radioscopy of the melt pool morphology for selective beam melting

PhD student: Maxence GUILLON, ED 488 SIS (Science, Engineering, Health)


Additive Manufacturing processes of metals, such as Laser Beam Melting or Direct Energy Deposition are popular processes to design objects with complex geometries and high density. The main phenomenon that control the process is the interaction between the laser and the material, which is in a powder form at the beginning. This powder bed is melted with a laser. This interaction allows to build a track which quality and integrity depend on the parameters used. This step is repeated, layer by layer, to obtain a 3D object. By controlling the parameters, a specific regime can be reached: the keyhole regime. In this regime, the density of energy is high and the laser can penetrate deeper in the material. Nevertheless, the stability windows are short and porosities can be easily formed into the material which weaken the build object.
The mechanisms of the keyhole regime are linked to the interactions between laser and material and the evolution of the behaviours of the melt pool surface. Indeed, the high energy density required let appear a high temperature gradient and surface tension gradient in the melt pool which generates Marangoni convection. Moreover, a strong metal evaporation creates a recoil pressure gradient around the laser beam.
The research work aims to observe the formation of keyholes by in situ radioscopy in. As a first step, a system will be elaborated in order to allow to build a powder-bed as fine as possible to enable the transparency of the X-ray during the process. The possibility of creating and using such systems is currently investigated. Single tracks will be built and post characterized. The dimensions of the melt pool and the keyholes as well as the microstructure resulting of it will be investigate. Then, the optimize system will be added at the high-energy dual tomography in the Mateis laboratory at INSA Lyon and the ESRF in Grenoble to make in situ radioscopy during additive manufacturing process.

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