Direkt metal sinterleme yöntemlerindeki sıcaklık alanlarının, artık gerilmelerin ve çarpılmaların modellenmesi

Additive manufacturing provides new opportunities for weight reduction in the aerospace industry where high fly-o-buy ratio is desired. Selective laser sintering of advanced engineering materials like Nickel super-alloys are also expanding to reduce the cost and time of the manufacturing in the aerospace industry. Elevated temperature and temperature gradients are critical factors in selective laser sintering of metals and they significantly affect the quality and integrity factors of produced parts such as microstructures, porosity, residual stresses and distortions. Therefore, an advanced simulation tool is needed to predict the temperatures, temperature gradients and molten pool geometries for a better understanding of the physics of the selective laser melting process as well as process optimizations. Moreover, it is essential to predict residual stresses and distortions so that preventive actions such as support design or changing build direction can be taken. Although researchers have been studying for more than a decade to understand and model the complex physical phenomena involved in the Direct Laser Metal Sintering (DMLS) process, the solutions provided in the literature are not fully applicable in industrial cases due to long computation time. This thesis, introduces an adjustable finite element based multi-physics and multi-software platform thermal model for direct metal laser sintering (powder bed systems) to predict the transient temperature and the molten pool geometry. The developed model is able to simulate 3D transient temperature and molten pool shape in the laser additive manufacturing process by including the features of melting and solidification, porous media and temperature-dependent thermal material properties for different materials. A set of experiments of Inconel 625 is carried out in order to measure the size of the molten pool and to validate the developed thermal model. An experimental study on temperature distribution carried out with Titanium and an experimental study on molten pool sizes carried out with Inconel 625 in the literature are also compared with the developed thermal model. The prediction errors of the developed model are in the range of 11 – 18 %. Moreover, an analytical approach and a multi-physics based finite element modeling approach are introduced in this thesis for quick estimation of the residual stresses and distortions of the parts in the direct metal laser sintering. The modeling approach incorporates the features of plasticity and hardening mechanism into the FEM environment. FEM simulation results on residual stress and distortions are validated by experimental measurements on Inconel 625. The simulation results agree with the experimental measurements within a range of 0.2 – 9%. Finally, the developed thermo-mechanical model is tested for complex freeform and thin-walled structures. Four freeform and seven thin-wall structures are additively manufactured and simulated. Experiments on thin wall hallow and complex freeform structures are performed in order to validate the developed model for the residual stresses and distortions in direct metal laser sintering process in industrial parts. The simulation results agree well with the experimental measurements. It should be noted that for the first time in the literature, additive manufacturing of industrial parts can be successfully simulated in much shorter computation time using the developed model. The unique model developed in this thesis is used in the aerospace industry in the thermal, residual stress and distortion simulations of additive manufactured engine parts of the unmanned air vehicles.