Development of a thermomechanical finite element model for laser powder bed fusion process and its comparison with inherent strain method
Bayraktar, Can (2021) Development of a thermomechanical finite element model for laser powder bed fusion process and its comparison with inherent strain method. [Thesis]
The Laser Powder Bed Fusion process as an additive manufacturing method is used for layer-by-layer production of metal components. In recent years, the process has attracted great attention from industries such as aerospace and automotive because of its ability to produce parts with complex geometries from materials with low machinability. However, residual stresses that build up during the process due to high thermal gradients negatively affect the overall quality and mechanical performance of the end product. Hence, further investigation is needed on the relationship between process parameters and residual stresses. In this study, a thermomechanical finite element model was developed for the estimation of thermal history and residual stresses by simulating the LPBF process. A commercial finite element software was used in combination with user-defined subroutines. A methodology was implemented to the thermomechanical model to express surface heat losses as a volumetric heat loss using Gauss’ theorem. This method eliminated the need to repeatedly define free surfaces after deposition of each layer. The model predicted the melt pool dimensions with a less than %10 error according to the experimental data. A parametric study was carried out to observe the impact of process parameters and scan pattern on melt pool size, maximum temperature and residual stresses. From the theory of inherent strain, a stress-based variant was developed to estimate stresses directly from a thermal solution. The developed method predicted the stresses with a maximum of %15 deviation in comparison to the thermomechanical solution and also computational time was decreased by six times.
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