316-L 스테인리스강의 레이저 분말 베드 융합 중 콜드 스패터 형성의 충실도 높은 수치 모델링
W.E. ALPHONSO1*, M. BAYAT1 and J.H. HATTEL1
*Corresponding author
1Technical University of Denmark (DTU), 2800, Kgs, Lyngby, Denmark
ABSTRACT
L-PBF(Laser Powder Bed Fusion)는 금속 적층 제조(MAM) 기술로, 기존 제조 공정에 비해 부품 설계 자유도, 조립품 통합, 부품 맞춤화 및 낮은 툴링 비용과 같은 여러 이점을 산업에 제공합니다.
전기 코일 및 열 관리 장치는 일반적으로 높은 전기 및 열 전도성 특성으로 인해 순수 구리로 제조됩니다. 따라서 순동의 L-PBF가 가능하다면 기하학적으로 최적화된 방열판과 자유형 전자코일을 제작할 수 있습니다.
그러나 L-PBF로 조밀한 순동 부품을 생산하는 것은 적외선에 대한 낮은 광 흡수율과 높은 열전도율로 인해 어렵습니다. 기존의 L-PBF 시스템에서 조밀한 구리 부품을 생산하려면 적외선 레이저의 출력을 500W 이상으로 높이거나 구리의 광흡수율이 높은 녹색 레이저를 사용해야 합니다.
적외선 레이저 출력을 높이면 후면 반사로 인해 레이저 시스템의 광학 구성 요소가 손상되고 렌즈의 열 광학 현상으로 인해 공정이 불안정해질 수 있습니다. 이 작업에서 FVM(Finite Volume Method)에 기반한 다중 물리학 중간 규모 수치 모델은 Flow-3D에서 개발되어 용융 풀 역학과 궁극적으로 부품 품질을 제어하는 물리적 현상 상호 작용을 조사합니다.
녹색 레이저 열원과 적외선 레이저 열원은 기판 위의 순수 구리 분말 베드에 단일 트랙 증착을 생성하기 위해 개별적으로 사용됩니다.
용융 풀 역학에 대한 레이저 열원의 유사하지 않은 광학 흡수 특성의 영향이 탐구됩니다. 수치 모델을 검증하기 위해 단일 트랙이 구리 분말 베드에 증착되고 시뮬레이션된 용융 풀 모양과 크기가 비교되는 실험이 수행되었습니다.
녹색 레이저는 광흡수율이 높아 전도 및 키홀 모드 용융이 가능하고 적외선 레이저는 흡수율이 낮아 키홀 모드 용융만 가능하다. 레이저 파장에 대한 용융 모드의 변화는 궁극적으로 기계적, 전기적 및 열적 특성에 영향을 미치는 열 구배 및 냉각 속도에 대한 결과를 가져옵니다.
Laser Powder Bed Fusion (L-PBF) is a Metal Additive Manufacturing (MAM) technology which offers several advantages to industries such as part design freedom, consolidation of assemblies, part customization and low tooling cost over conventional manufacturing processes. Electric coils and thermal management devices are generally manufactured from pure copper due to its high electrical and thermal conductivity properties. Therefore, if L-PBF of pure copper is feasible, geometrically optimized heat sinks and free-form electromagnetic coils can be manufactured. However, producing dense pure copper parts by L-PBF is difficult due to low optical absorptivity to infrared radiation and high thermal conductivity. To produce dense copper parts in a conventional L-PBF system either the power of the infrared laser must be increased above 500W, or a green laser should be used for which copper has a high optical absorptivity. Increasing the infrared laser power can damage the optical components of the laser systems due to back reflections and create instabilities in the process due to thermal-optical phenomenon of the lenses. In this work, a multi-physics meso-scale numerical model based on Finite Volume Method (FVM) is developed in Flow-3D to investigate the physical phenomena interaction which governs the melt pool dynamics and ultimately the part quality. A green laser heat source and an infrared laser heat source are used individually to create single track deposition on pure copper powder bed above a substrate. The effect of the dissimilar optical absorptivity property of laser heat sources on the melt pool dynamics is explored. To validate the numerical model, experiments were conducted wherein single tracks are deposited on a copper powder bed and the simulated melt pool shape and size are compared. As the green laser has a high optical absorptivity, a conduction and keyhole mode melting is possible while for the infrared laser only keyhole mode melting is possible due to low absorptivity. The variation in melting modes with respect to the laser wavelength has an outcome on thermal gradient and cooling rates which ultimately affect the mechanical, electrical, and thermal properties.
Keywords
Pure Copper, Laser Powder Bed Fusion, Finite Volume Method, multi-physics
References
[1] L. Jyothish Kumar, P. M. Pandey, and D. I. Wimpenny, 3D printing and additive
manufacturing technologies. Springer Singapore, 2018. doi: 10.1007/978-981-13-0305-0.
[2] T. DebRoy et al., “Additive manufacturing of metallic components – Process, structure
and properties,” Progress in Materials Science, vol. 92, pp. 112–224, 2018, doi:
10.1016/j.pmatsci.2017.10.001.
[3] C. S. Lefky, B. Zucker, D. Wright, A. R. Nassar, T. W. Simpson, and O. J. Hildreth,
“Dissolvable Supports in Powder Bed Fusion-Printed Stainless Steel,” 3D Printing and
Additive Manufacturing, vol. 4, no. 1, pp. 3–11, 2017, doi: 10.1089/3dp.2016.0043.
[4] J. L. Bartlett and X. Li, “An overview of residual stresses in metal powder bed fusion,”
Additive Manufacturing, vol. 27, no. January, pp. 131–149, 2019, doi:
10.1016/j.addma.2019.02.020.
[5] I. H. Ahn, “Determination of a process window with consideration of effective layer
thickness in SLM process,” International Journal of Advanced Manufacturing
Technology, vol. 105, no. 10, pp. 4181–4191, 2019, doi: 10.1007/s00170-019-04402-w.
[6] R. McCann et al., “In-situ sensing, process monitoring and machine control in Laser
Powder Bed Fusion: A review,” Additive Manufacturing, vol. 45, no. May, 2021, doi:
10.1016/j.addma.2021.102058.
[7] M. Bayat et al., “Keyhole-induced porosities in Laser-based Powder Bed Fusion (L-PBF)
of Ti6Al4V: High-fidelity modelling and experimental validation,” Additive
Manufacturing, vol. 30, no. August, p. 100835, 2019, doi: 10.1016/j.addma.2019.100835.
[8] M. Bayat, S. Mohanty, and J. H. Hattel, “Multiphysics modelling of lack-of-fusion voids
formation and evolution in IN718 made by multi-track/multi-layer L-PBF,” International
Journal of Heat and Mass Transfer, vol. 139, pp. 95–114, 2019, doi:
10.1016/j.ijheatmasstransfer.2019.05.003.
[9] S. D. Jadhav, L. R. Goossens, Y. Kinds, B. van Hooreweder, and K. Vanmeensel, “Laserbased powder bed fusion additive manufacturing of pure copper,” Additive Manufacturing,
vol. 42, no. March, 2021, doi: 10.1016/j.addma.2021.101990.
[10] S. D. Jadhav, S. Dadbakhsh, L. Goossens, J. P. Kruth, J. van Humbeeck, and K.
Vanmeensel, “Influence of selective laser melting process parameters on texture evolution
in pure copper,” Journal of Materials Processing Technology, vol. 270, no. January, pp.
47–58, 2019, doi: 10.1016/j.jmatprotec.2019.02.022.
[11] H. Siva Prasad, F. Brueckner, J. Volpp, and A. F. H. Kaplan, “Laser metal deposition of
copper on diverse metals using green laser sources,” International Journal of Advanced
Manufacturing Technology, vol. 107, no. 3–4, pp. 1559–1568, 2020, doi: 10.1007/s00170-
020-05117-z.
[12] L. R. Goossens, Y. Kinds, J. P. Kruth, and B. van Hooreweder, “On the influence of
thermal lensing during selective laser melting,” Solid Freeform Fabrication 2018:
Proceedings of the 29th Annual International Solid Freeform Fabrication Symposium – An
Additive Manufacturing Conference, SFF 2018, no. December, pp. 2267–2274, 2020.
[13] M. Bayat, V. K. Nadimpalli, D. B. Pedersen, and J. H. Hattel, “A fundamental investigation
of thermo-capillarity in laser powder bed fusion of metals and alloys,” International
Journal of Heat and Mass Transfer, vol. 166, p. 120766, 2021, doi:
10.1016/j.ijheatmasstransfer.2020.120766.
[14] H. Chen, Q. Wei, Y. Zhang, F. Chen, Y. Shi, and W. Yan, “Powder-spreading mechanisms
in powder-bed-based additive manufacturing: Experiments and computational modeling,”
Acta Materialia, vol. 179, pp. 158–171, 2019, doi: 10.1016/j.actamat.2019.08.030.
[15] S. K. Nayak, S. K. Mishra, C. P. Paul, A. N. Jinoop, and K. S. Bindra, “Effect of energy
density on laser powder bed fusion built single tracks and thin wall structures with 100 µm
preplaced powder layer thickness,” Optics and Laser Technology, vol. 125, May 2020, doi:
10.1016/j.optlastec.2019.106016.
[16] G. Nordet et al., “Absorptivity measurements during laser powder bed fusion of pure
copper with a 1 kW cw green laser,” Optics & Laser Technology, vol. 147, no. April 2021,
p. 107612, 2022, doi: 10.1016/j.optlastec.2021.107612.
[17] M. Hummel, C. Schöler, A. Häusler, A. Gillner, and R. Poprawe, “New approaches on
laser micro welding of copper by using a laser beam source with a wavelength of 450 nm,”
Journal of Advanced Joining Processes, vol. 1, no. February, p. 100012, 2020, doi:
10.1016/j.jajp.2020.100012.
[18] M. Hummel, M. Külkens, C. Schöler, W. Schulz, and A. Gillner, “In situ X-ray
tomography investigations on laser welding of copper with 515 and 1030 nm laser beam
sources,” Journal of Manufacturing Processes, vol. 67, no. April, pp. 170–176, 2021, doi:
10.1016/j.jmapro.2021.04.063.
[19] L. Gargalis et al., “Determining processing behaviour of pure Cu in laser powder bed
fusion using direct micro-calorimetry,” Journal of Materials Processing Technology, vol.
294, no. March, p. 117130, 2021, doi: 10.1016/j.jmatprotec.2021.117130.
[20] A. Mondal, D. Agrawal, and A. Upadhyaya, “Microwave heating of pure copper powder
with varying particle size and porosity,” Journal of Microwave Power and
Electromagnetic Energy, vol. 43, no. 1, pp. 4315–43110, 2009, doi:
10.1080/08327823.2008.11688599.