Comparison of Finite-Element Methodologies Used for Predicting Final Part Distortion and Residual Elastic Strains in Selective Laser Melting Additively Manufactured Parts

This study is a comparison of finite element-based methodologies used for predicting final part distortion and residual elastic strains of IN625 parts produced via selective laser melting (SLM) additive manufacturing (AM). It has been well documented that parts produced via SLM undergo temperature gradients in the vertical build direction during fabrication. This thermal gradation can impact final part quality and microstructure in terms of final part distortion and mechanical properties as a result of built-up residual stresses due to a varying thermal history. It has also been determined in the literature that these residual stresses and thermal histories are tied to SLM process parameters such as laser power and scan speed. However, there is no quantified process-property relationship between process parameters and final part attributes such as distortion and microstructure published to date.

The focus of this work is to contrast the reliability, accuracy, and effectiveness of final part distortion and residual elastic strain predictions for IN625 parts produced with SLM by NetFabb 2020, Abaqus 2019, and a sequentially coupled thermomechanical simulation utilizing an IN625 elastic-plastic user subroutine with the Abaqus 2019 solver. With the lack of a process-property relationships and the need to avoid empirically determining an optimized set of process parameters for each material and part geometry, it is advantageous to develop computational thermomechanical models to predict final part distortion and other part attributes with respect to input process parameters. To this end, computational software packages such as NetFabb and Abaqus have started to include thermomechanical modeling tools to help engineers account for distortions and residual stresses in their designs and calibrate process parameters for refinement.

To maintain similarities between each finite-element methodology, the machine process parameters used for the heat source model, the material of IN625, and the geometry were held constant and in accordance with the 2018 National Institute of Standards and Technology (NIST) AM benchmark test results. The SLM machine selected was an EOS M270 and the specimen geometry used was a 75 mm long, 12 mm tall, and 5 mm wide part to correspond with the 2018 NIST AM benchmark’s commercial build machine and geometry, respectively. The accuracy and reliability of each finite-element methodology was determined by measuring the deviation between the simulated results of each modeling approach with the 2018 NIST AM benchmark test measurements for final part distortion and residual elastic strain. Lastly, the effectiveness of each methodology was determined by contrasting the computational time needed for each method.