What did the Scientists Discover?
Laser powder bed fusion (L-PBF) additive manufacturing (AM) of metal parts provide signiffcant beneffts over traditional manufacturing processes, including the creation of parts with more geometric complexity. However, due to the large thermal gradients and cooling rates inherent to the process, parts produced via L-PBF often contain high levels of residual stress and experience signiffcant distortion. In order for components produced via L-PBF to be used in critical applications, they need to meet tight tolerances and a high degree of conffdence is required in their quality. In this work, researchers developed an advanced computational model to predict the residual stress state in a bridge shaped part and compared the simulated data with experimental results obtained at CHESS, finding good qualitative and quantitative agreement.
Why is this important?
The agreement between the measured and simulated strain results allows for conffdence in using the simulation results to visualize the complete stress state throughout the part, supplementing the measurements which were performed along a single cross-sectional plane. Another signiffcant outcome of this work was the measured presence of higher residual strains, especially near part boundaries. Potential explanations could be higher cooling rates and thermal gradients in these regions.
What are the broader impacts of this work?
High ffdelity simulations, combined with a more physical representation of the heat input, allow to accurately apture differences in process parameters. With that simulations will be able to predict the most suitable build parameters for L-PBF additive manufacturing (AM) for any given part.
Why did this research need CHESS?
The energy dispersive diffraction experiments were performed at the A2 station of CHESS. The high-energy, polychromatic X-ray beam provided a unique combination of penetration depth and spatial measurement resolution (in comparison to time-of-flight neutron measurements) necessary to probe the residual stress gradients throughout the metallic part. In December 2019, a laser powder bed fusion (L-PBF) additive manufacturing (AM) system is scheduled to be installed at the CHEXS FAST beamline which will make it possible to monitor these build processes in-situ.
Collaborators:
- R.K.Ganeriwala, Lawrence Livermore National Laboratory
- M.Strantza, Los Alamos National Laboratory
- W.E.King. Lawrence Livermore National Laboratory
- B.Clausen, Los Alamos National Laboratory
- T.Q.Phan, National Institute of Standards and Technology
- L.E.Levine, National Institute of Standards and Technology
- D.W.Brown, Los Alamos National Laboratory
- N.E.Hodge, Lawrence Livermore National Laboratory
Publication Citation:
Ganeriwalaa, R.K. et al., “Evaluation of a thermomechanical model for prediction of residual stress during laser powder bed fusion of Ti-6Al-4V,” Additive Manufacturing, vol. 27, pp. 489-502, May 2019. https://www.sciencedirect.com/science/article/pii/S2214860418308741
How was the work funded?
This work at Lawrence Livermore National Laboratory was supported by DOE under contract DE-AC52-07NA27344 and at Los Alamos National Laboratory under contract DE-AC52-06NA25396. CHESS was supported by NSF award DMR-1332208. CHEXS is supported by NSF award DMR-1829070.