Residual Strain Predictions for a Powder Bed Fusion Inconel 625 Single Cantilever Part

Abstract

The laser powder bed fusion (LPBF) process involves using a laser beam to selectively melt metal powder with a desired shape on a substrate to create a part layer-by-layer. As an Additive Manufacturing (AM) process, laser powder bed fusion (commonly referred to as selective laser melting-SLM) offers superior design freedom over conventional manufacturing methods and enables the production of complex, lightweight geometries with applications in the aerospace, automotive, and biomedical industries. In addition to enhanced design freedom, AM technologies provide improved material utilization and allow for reduced assembly needs. However, the reliability and repeatability of additively manufactured parts is a challenge to the wide-scale adoption of the technology for safety critical parts. A critical limitation of process optimization is the prediction and control of residual stresses, distortion, and microstructure evolution. This work focuses on the development and implementation of a numerical modeling technique for the prediction of residual strains within an Inconel 625 LPBF part. The model, using the SIMULIA Additive Manufacturing Scenario App, based on the Abaqus 2018 finite element solver, was developed and analyzed as part of a submission for the NIST AM Benchmark 2018. A sequentially coupled thermo-mechanical analysis was adopted to replicate the building conditions of a single cantilever beam built at the NIST laboratories. The results of the blind study were compared to X-ray diffraction (XRD) measurements of the physical build. The predicted three-dimensional residual strain field showed a high level of accuracy and the submission described in this paper received joint first prize in the residual elastic strain category of the NIST AM Benchmark 2018. The results presented in this paper reflect only findings before the benchmark measurements were posted on the NIST website.

Modeling and experimental validation of an immersed thermo-mechanical part-scale analysis for laser powder bed fusion processes

“…On the contrary, a standard FEM approach using such a coarse dis-cretization along the growing direction would lead to less accurate results since the geometry cannot be represented with sucient accuracy anymore. Clearly, for the present benchmark numerical simulations can be obtained also by means of classical FEM codes, e.g., in Yang et al [19] an excellent agreement with the measured stains of the nal structure is obtained using ABAQUS AM R .…”

“…In the present work, we employ a similar physical model, following an extension of the pragmatic approach as proposed in [19].…”

“…mechanical behavior during both the manufacturing process and the support removal stage. Following the pragmatic approach, we instantiate the new Gauss point temperature value at the so-called relaxation temperature dened as the temperature above which thermal strain induces negligible thermal stress[19], which for IN625 is 750 • C.Once the entire LPBF process is simulated and the nal residual stresses within the component are computed, a part-removal step is carried out where the base plate cells are progressively removed and the nal deection of the artifact is calculated.…”

Outcomes and Conclusions from the 2018 AM-Bench Measurements, Challenge Problems, Modeling Submissions, and Conference

“…Of the six blind submissions for the residual strain challenge, two stood out by qualitatively matching all of the observed spatially varying strains. One of these teams has a paper in this special issue [27]. For the winning teams, quantitative comparison between submitted simulation predictions and the measurement results shows that the accuracy of the predicted strains is not uniform throughout the part.…”

Survey of Modeling and Simulation Techniques for Advanced Manufacturing Technologies Volume II – Predicting Material Performance from Material Microstructure

“…Similar to the AFRL challenge, the team used the SIMULIA Additive Manufacturing Scenario App to perform a coupled thermo-mechanical analysis of the AMT component with local activation of elements. Their results led to a publication that highlighted the abilities of their software for the prediction of mechanical responses (Figure 6.2) [202]. Within the same benchmark, the PRISM research group from the university of Birmingham was awarded the firstplace prize for predicting the phase evolution during residual stress annealing of an as-built IN625 bridge structure [201].…”