Abstract
This work reports on employing X-ray computed tomography (XCT) to develop a predictive model aimed at optimizing laser process parameters for laser powder bed fusion. A commercially available statistical analysis software was successfully combined with XCT obtained porosity data obtained from 316L stainless steel to develop an accurate model that predicted the parameter sets and ranges with the lowest porosity. The predictions indicated that laser velocity and hatch spacing had a numerically linear relationship with laser power and can be combined to minimize porosity at any selected laser power in a specific range. In fact, the predictions indicated that the minimum porosity at any laser power is associated with a specific line energy input of approximately 0.13 J/mm for this alloy. The lowest predicted porosity at each laser power was fabricated and tested with the 85- and 92-W powers confirming ultra-low porosity. Lower laser powers, however, exhibited significantly higher porosity in contrast with the prediction. This resulted from the lower hatch spacing and velocity causing higher energy density and metallurgical defects from macro-balling. Thermodynamic calculations in the optimum laser power range yielded a line energy of 0.131 J/mm, which agrees rather well with the XCT predicted line energy and indicates that porosity generation is governed by the thermo-physical behavior of the alloy. A parameter space in the optimum range was fabricated and confirmed that the lowest porosities exist along a line energy of 0.13 J/mm, where melt pool temperature was predicted to be between 2526 and 2785 °C.
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Funding
This work was sponsored by the United States National Institute of Standards and Technology under contracts NIST-70NANB16H272, NIST-70NANB17H295, and NIST-70NANB18H220.
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RZ contributed to the study conception and design. Material preparation and data collection and analysis were performed by RZ, AS, RF, and BP. The first draft of the manuscript was written by RZ and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.
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The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: BCP reports financial support provided by the National Institute of Standards and Technology.
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Zhao, R., Shmatok, A., Fischer, R.D. et al. Linking alloy thermo-physical behavior to laser process parameters for density optimization in LPBF. Int J Adv Manuf Technol 129, 3171–3183 (2023). https://doi.org/10.1007/s00170-023-12501-y
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DOI: https://doi.org/10.1007/s00170-023-12501-y