Distortion Prediction in Selective Laser Melting: Methodology for Inherent Strain Determination

One of the process variants in metal additive manufacturing (AM) is the Selective Laser Melting (SLM) where parts are built on a layer by layer basis. A focused power source is applied (laser or electron beam) to the powder material which is rapidly heated above its melting temperature and then allowed to solidify and cool down to form a new solid layer. Typically, this manufacturing process induces residual stresses and distortions. Distortions are critical since they increase manufacturing costs, times and generate wastes and scraps due to dimensional inaccuracies. Therefore, a priori prediction of these distortions at design stage is preferred to trial and error strategy usually employed.
The detailed transient thermo-mechanical analysis (DTA) is commonly considered as the reference modelling strategy for AM processes. Nevertheless, the use of simplified methodologies, such as the Inherent Strain Method, is required in order to overcome the large computational cost needed by the DTA.
This work copes with the analysis, development and application of the Inherent Strain Method for the prediction of the final distortions in powder bed based SLM process. The main objective is to assess the predictive capability of this simplified model based on the inherent strain calibration strategy developed for that purpose. The assessment has been conducted correlating numerical results and experimental measurements in some testing geometries.