Ultrafast X-ray imaging of laser–metal additive manufacturing processes

Parab, Niranjan D.; Zhao, Cang; Cunningham, Ross; Escano, Luis I.; Fezzaa, Kamel; Everhart, Wes; Rollett, Anthony D.; Chen, Lianyi; Sun, Tao

doi:10.1107/s1600577518009554

Cited by 158 publications

(76 citation statements)

References 45 publications

(18 reference statements)

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“…The experimental schematic is shown in Fig. S1 of the Supplemental Material [6], with the details in Appendix A [7,23,24]. Figure 1 and Supplemental Material Fig.…”

Section: A Mhz Synchrotron-x-ray Imaging Of Laser-induced Spatteringmentioning

confidence: 99%

Bulk-Explosion-Induced Metal Spattering During Laser Processing

Zhao

Guo

et al. 2019

Phys. Rev. X

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Spattering has been a problem in metal processing involving high-power lasers, like laser welding, machining, and recently, additive manufacturing. Limited by the capabilities of in situ diagnostic techniques, typically imaging with visible light or laboratory x-ray sources, a comprehensive understanding of the laser-spattering phenomenon, particularly the extremely fast spatters, has not been achieved yet. Here, using MHz single-pulse synchrotron-x-ray imaging, we probe the spattering behavior of Ti-6Al-4V with micrometer spatial resolution and subnanosecond temporal resolution. Combining direct experimental observations, quantitative image analysis, as well as numerical simulations, our study unravels a novel mechanism of laser spattering: The bulk explosion of a tonguelike protrusion forming on the front keyhole wall leads to the ligamentation of molten metal at the keyhole rims and the subsequent spattering. Our study confirms the critical role of melt and vapor flow in the laser-spattering process and opens a door to manufacturing spatter-and defect-free metal parts via precise control of keyhole dynamics.

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“…The experimental schematic is shown in Fig. S1 of the Supplemental Material [6], with the details in Appendix A [7,23,24]. Figure 1 and Supplemental Material Fig.…”

Section: A Mhz Synchrotron-x-ray Imaging Of Laser-induced Spatteringmentioning

confidence: 99%

Bulk-Explosion-Induced Metal Spattering During Laser Processing

Zhao

Guo

et al. 2019

Phys. Rev. X

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“…However, the dynamics of particle-scale powder spreading was not revealed, due to the limited resolution and penetration depth of conventional characterization tools. Very recently, our team, as well as other research groups, have demonstrated that high-energy x-ray imaging could penetrate metals to study powder spattering, melting, and pore evolution during metal additive manufacturing process 24 – 28 , indicating that x-ray imaging could be a powerful tool for studying powder spreading process.…”

Section: Introductionmentioning

confidence: 96%

Revealing particle-scale powder spreading dynamics in powder-bed-based additive manufacturing process by high-speed x-ray imaging

Escano

Parab

Xiong

et al. 2018

Sci Rep

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101

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Powder spreading is a key step in the powder-bed-based additive manufacturing process, which determines the quality of the powder bed and, consequently, affects the quality of the manufactured part. However, powder spreading behavior under additive manufacturing condition is still not clear, largely because of the lack of particle-scale experimental study. Here, we studied particle-scale powder dynamics during the powder spreading process by using in-situ high-speed high-energy x-ray imaging. Evolution of the repose angle, slope surface speed, slope surface roughness, and the dynamics of powder clusters at the powder front were revealed and quantified. Interactions of the individual metal powders, with boundaries (substrate and container wall), were characterized, and coefficients of friction between the powders and boundaries were calculated. The effects of particle size on powder flow dynamics were revealed. The particle-scale powder spreading dynamics, reported here, are important for a thorough understanding of powder spreading behavior in the powder-bed-based additive manufacturing process, and are critical to the development and validation of models that can more accurately predict powder spreading behavior.

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“…Previous work has established a link between the shape of pores and cooling rate 2 , however, a more fundamental understanding of this process still needs to be fully established. Highspeed synchrotron imaging can provide adequate spatial and temporal resolutions to capture critical phenomena such as melt pool dynamics, powder entrainment, and defect formation [3][4][5] . In this study, the high-speed synchrotron X-ray imaging technique at the Advanced Photon Source (APS) is used to observe dynamic phenomena involved in the DED process.…”

mentioning

confidence: 99%

Porosity Formation and Meltpool Geometry Analysis Using High-speed, in situ Imaging of Directed Energy Deposition

et al. 2019

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While directed energy deposition (DED) can provide tremendous flexibility in both geometry and materials, there are still many challenges that need to be overcome before this technology can be freely used in industry 1 . Previous work has established a link between the shape of pores and cooling rate 2 , however, a more fundamental understanding of this process still needs to be fully established. Highspeed synchrotron imaging can provide adequate spatial and temporal resolutions to capture critical phenomena such as melt pool dynamics, powder entrainment, and defect formation [3][4][5] . In this study, the high-speed synchrotron X-ray imaging technique at the Advanced Photon Source (APS) is used to observe dynamic phenomena involved in the DED process. Different from previous publications, this work was carried out using an innovative home-built high-throughput DED apparatus, where a large range of process parameters could be effectively studied without the need of constantly opening the chamber to load new samples and spending time re-aligning them. This largely increased the experiment efficiency. The DED setup consists of an aluminum enclosure, a DMG single powder nozzle, a motorized sample drum, a 500 W continuous wave ytterbium fiber laser, and a fast motorized stage for deposition. The enclosure was filled with Argon during experiments to prevent excessive oxidation. The substrates to be deposited on were 50 mm by 10 mm thin rectangle plates cut from 406 µm thick sheets of Grade 5 Titanium alloy (Ti-6Al-4V). The powder used in deposition was 45-150 µm Ti-6Al-4V, and Argon carrier/shield gas was used in the nozzle. Ti-6Al-4V was chosen because it is one of most commonly used materials in metal AM and has many important applications in the fields of aerospace and aviation. The parameters in this study can be combined to define the 'effective global energy density', GED' = P/(PF•V•A), where P is the laser power, PF is the powder flow rate, V is the scan speed, and A is the beam area. GED' represents the ratio of energy to mass that is added to the sample and is an effective way to describe DED from an input parameter perspective. Since the power density of the laser used in the experiment is higher than that in a commercial DED process, the scan speeds chosen were also faster. In the experiment, the beamline components and the DED system were controlled collectively using a series of delay generators. A typical procedure is: X-ray shutters open, powder nozzle turns on, deposition stage accelerates to steady state, imaging camera turns on, fiber laser turns on and melts the powder in the X-ray window, X-ray shutters close. One example of parameters used in the experiments are: 300 W laser power, 500 mg/s powder flow rate, and 100 mm/s scan speed. Images were taken at 80,000 fps in a 2 mm  2 mm window.Observed phenomena include pore formation, melt pool geometry and fluctuations, and powder particle capture. Representative X-ray images are shown in Fig. 1. Here, the generation of pores in the melt pool can be ...

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Ultrafast X-ray imaging of laser–metal additive manufacturing processes

Cited by 158 publications

References 45 publications

Bulk-Explosion-Induced Metal Spattering During Laser Processing

Bulk-Explosion-Induced Metal Spattering During Laser Processing

Revealing particle-scale powder spreading dynamics in powder-bed-based additive manufacturing process by high-speed x-ray imaging

Porosity Formation and Meltpool Geometry Analysis Using High-speed, in situ Imaging of Directed Energy Deposition

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