Characterization and quantification of mechanisms influencing the process reliability of Laser Beam Melting by experimental and numerical investigations

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The aim of the proposed research project is an advancement of the knowledge on additive manufacturing processes, which employ lasers beams for melting metal powders. The planned investigations will consider the process of cooling and solidification of the molten metal as well as the evaporation of liquid metal, which influences process characteristics and product quality, especially with respect to the occurrence of pores. Also thermally induced residual stresses in vicinity of the heating zone will be analyzed. The focus of the proposed project will be the analysis of the interactions between on one side the selected process parameters (e.g. laser power, scanning speed), the materials employed (heat conductivity, enthalpies of phase changes, powder particle size and shape) and on the other side the fluid- and thermodynamic effects in the melt pool (convection, Marangoni-effect, evaporation, liquid surface topology and laser beam reflections etc.). The obtained insights will allow for more stable beam melting processes and also help to reduce reject rates in production, reduce the number of test runs for new part designs and also allow to shorten the testing program when qualifying new materials.Initially an experimental process analysis is conducted in order to estimate the extent of influence of major process parameters on the process stability. In the following the mechanisms of interaction are investigated in greater detail and are also quantified employing experiments as well as numerical simulations. For the first time the method of smoothed particle hydrodynamics (SPH) will be applied for the simulation of laser beam melting. With SPH fluids and solids are described by Lagrangian particles, which carry properties of the respective phase. Local macroscopic values, such as temperature, are recovered by averaging operations using all particles in vicinity of the position considered. Judging by todays state of technology and our preliminary work, SPH methods will allow for a highly efficient handling of multiple phase changes and of powder layers featuring complex geometries. This will enable simulations of laser beam melting taking into account all relevant physical mechanisms. Experimental investigations will be conducted to validate the numerical method and broaden the knowledge on the melting process. In order to adequately capture rapid transient processes, suitable measurement techniques will be evaluated and adopted to the problem. For investigations of melt pool dynamics and also of the blow-away effect of powder particles from the heating zone due to application of shielding gases and also due to evaporation of the melt, high-speed cameras will be employed.