Determining the three-dimensional residual stress fields and the associated distortions using numerical simulations for multi-layered parts has proved to be a challenge in additive layer manufacturing. This paper presents an innovative three-dimensional thermal-elasto-plastic finite element model for predicting the deformation and residual stress fields in TiAl6V4 parts built on steel platforms. The developed model utilises temperature dependent material physical and mechanical properties as well as latent heat of melting. Experiments conducted using surface profilometry showed good agreement with the simulation results. The finite element model was used to investigate the overall effect of the melting powder on the platform deformation and residual stresses for multiple layers of deposited powder.
Abstract. The direct impingement of laser on the surface of a platform occurs during additive layer manufacturing especially for the first layer of powder coating. As a result, thermal stresses develop due to high temperature gradients in a thin layer of the plate surface, which can result in undesired surface deformation of the steel platform used. This study investigates the residual stress profiles on a hot-rolled AISI 1015 steel plate produced by direct laser application. A three-dimensional finite element simulation model is developed which considers the laser heating process as a sequentially coupled thermal elasto-plastic problem. Experiments using optical laser scanning microscopy to obtain surface topography of the melted surface are also presented showing reasonable agreement with the simulation results. The influence of the plate thickness on the stress-depth distribution is presented.
The Metal Laser Sintering (MLS) process has been developed over the last decade to produce 3D parts from CAD files using metal powders. A considerable amount of research has been conducted into the melting and solidifying process of metal powders, mainly to predict the temperature distribution in a single metal powder layer or a few layers. The temperature and thermal residual stress distribution in real parts built using MLS has rarely been reported. Finite element simulations of temperature distributions in metal powders and parts requires huge computing resources, this is the main obstacle to successfully predicting temperature and thermal stress distributions in MLS parts. However, from the numerical results in this paper, the periodic nature of temperature distributions in parts around the laser spot can be used to simplify the numerical simulation process to achieve the prediction of temperature and thermal stresses distributions in parts built by MLS.
The Iron Bridge completed in 1779 was the world’s first bridge. It is located at the world heritage site of Ironbridge Gorge in Shropshire, England. In order to predict the stress distribution and deformation in the bridge, the Iron Bridge was modelled and analysed using the finite element method. The maximum tensile stress was predicted to occur in the strut close to the middle of the bridge, which could be the reason why the strut failed. The numerically predicted deformations in the circles and ogees in the Iron Bridge are in agreement with the observed deformations. It is concluded that for the conservation and maintenance of the historic Iron Bridge, modern numerical simulations are invaluable for providing guidance.
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