In situ diffraction during Selective Laser Melting

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Selective Laser Melting (SLM) is a relatively young and very complex manufacturing process compared to conventional manufacturing methods, which is why the fundamental understanding of the process is still insufficiently developed. This results in a partial lack of reproducibility of the results, which impedes an industrial application for series production. In the process, this manifests itself through distortions and cracks in the components, which can cause both component defects and machine defects. This joint research project aims to acquire a deeper process knowledge in order to be able to minimize the causes of process interruptions and insufficient component quality, i.e. distortion and crack formation, and thus improve the reproducibility of the process. For this purpose, the method of in situ diffraction is used to measure and describe the processes of stress formation, texture development and phase transformations in the SLM process during the solidification of individual layers. The measurements are carried out by means of high-energy synchrotron radiation on a self-developed experimental SLM setup during the production of test parts. With the knowledge gained about the stress formation in the work piece, process errors can be specifically analyzed and influenced. The influence of different geometries, process parameters and temperature profiles on the residual stresses will be investigated using test parts made of the nickel-based alloy Inconel 625 (IN625) and commercially pure titanium grade 1 (TiGrI). These two materials are characterized by their wide range of applications while exhibiting different structural properties at the same time. The expected results and data contribute to the clarification of the basic physical relationships in the process, which in turn will enable optimizing the process as a whole and form the basis for a subsequent modelling. The quantitative results also serve as input variables for the representation of the functional relationships between process parameters and residual stress states as a result of the cyclic heating and cooling during the successive application of layers in future simulations.