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Characterizing the effects of laser control in laser powder bed fusion on near-surface pore formation via combined analysis of in-situ melt pool monitoring and X-ray computed tomography

Published

Author(s)

Felix Kim, Ho Yeung, Edward Garboczi

Abstract

Background: Near-surface or sub-surface pores are critical to the structural integrity of additively manufactured (AM) parts, especially in fatigue failure applications. However, their formation in laser powder bed fusion is not well-understood due to the complex processes happening near the surface, which are challenging to monitor. A lack of high-fidelity data hinders understanding of the process and its effects. Objectives: We investigated the characteristics of the near-surface pores formed due to intricate laser control (galvanometer acceleration and laser turn on/off delay) of laser powder bed fusion (LPBF) AM processes. We also demonstrate the capabilities and processes of correlative studies using in-situ melt-pool images and ex-situ XCT images. Methods: Using the NIST additive manufacturing metrology testbed (AMMT), sophisticated laser control was implemented while in-situ coaxial melt-pool images were acquired. A combination of time-stepped digital commands, in-situ coaxial melt-pool monitoring images (≈ 8 µm/pixel), and ex-situ high-resolution X-ray Computed Tomography (XCT) images (≈ 3.63 µm/voxel) were demonstrated. Advanced image analysis methods were used to characterize the pores found in terms of size and shape distribution and spatial location. Results: XCT images clearly show the effects of the laser control parameters with high correlation to the melt-pool images. We present the complete correlation analysis chain of AM command, in-situ melt-pool imaging, ex-situ XCT acquisition, and image analysis. Conclusions: Possible pore formation mechanisms are explained through the correlative analysis. The approach of correlating time-stepped digital commands, in-situ monitoring results, and ex-situ XCT measurement through image analysis is a promising method to understand sophisticated issues that often arise in AM LBPF processes.
Citation
Additive Manufacturing
Volume
48

Keywords

additive manufacturing, defects, in-situ monitoring, X-ray Computed Tomography, Correlation, sub-surface pores, near-surface pores, pores, melt pool images

Citation

Kim, F. , Yeung, H. and Garboczi, E. (2021), Characterizing the effects of laser control in laser powder bed fusion on near-surface pore formation via combined analysis of in-situ melt pool monitoring and X-ray computed tomography, Additive Manufacturing, [online], https://doi.org/10.1016/j.addma.2021.102372, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=931661 (Accessed September 28, 2022)
Created October 4, 2021, Updated February 23, 2022