Energy-Coupling Mechanisms Revealed through Simultaneous Keyhole Depth and Absorptance Measurements during Laser-Metal Processing

Allen, Troy R.; Huang, Wenkang; Tanner, Jack; Tan, Wenda; Fraser, James M.; Simonds, Brian J.

doi:10.1103/physrevapplied.13.064070

Cited by 63 publications

(29 citation statements)

References 56 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In particular, this methodology may be able to link the occurrence between geometric fluctuations of the keyhole and localized events such as a pore pinching off at the bottom of the keyhole. In addition, since the laser absorptivity is highly dependent on keyhole geometry [27,28], this method may be effective for quantifying the changes in the laser absorptivity throughout the fluctuations of the keyhole so that a direct correlation between keyhole geometry and laser energy absorptance can be revealed experimentally.…”

Section: Discussion Of the Resultsmentioning

confidence: 99%

Time-Resolved Geometric Feature Tracking Elucidates Laser-Induced Keyhole Dynamics

Pyeon

Aroh

Jiang

et al. 2021

Integr Mater Manuf Innov

View full text Add to dashboard Cite

During laser melting of metals, localized metal evaporation resulting in the formation of a keyhole shaped cavity can occur if processing conditions are chosen with high power density. An unstable keyhole can have deleterious effects in certain applications (e.g., laser powder bed fusion) as it increases the likelihood of producing defects such as porosity. In this work, we propose a pipeline that enables complete segmentation and extraction of various geometric features in keyholing conditions. In situ synchrotron high-speed X-ray visualization at the Advanced Photon Source provides large datasets of experimental images with a high spatio-temporal resolution across a range of laser parameters for Ti-6Al-4V. Computer vision image processing techniques were used to extract time-resolved quantitative geometric features (e.g., depth, width, front wall angle) throughout keyhole evolution which were subsequently analyzed to understand the relationship between the variation of local keyhole geometry and processing conditions. This analysis is the first to employ a data-driven approach to further our understanding of the keyholing process regime.

show abstract

Section: Discussion Of the Resultsmentioning

confidence: 99%

Time-Resolved Geometric Feature Tracking Elucidates Laser-Induced Keyhole Dynamics

Pyeon

Aroh

Jiang

et al. 2021

Integr Mater Manuf Innov

View full text Add to dashboard Cite

show abstract

“…Intense evaporation and recoil pressure at the keyhole bottom can be further amplified by the rapid formation of a vapour cavity ("J-shaped" keyhole, Fig. 1e-ii), which traps reflected laser light and metal vapour, increasing the number and density of multiple reflections 8,18 and building up a significant stagnation pressure 12 . With energy concentrated in this cavity, the keyhole is prone to capillary instability and may sometimes collapse, pinching off a cavity to form a vapour filled bubble (Fig.…”

Section: Fig S5)mentioning

confidence: 99%

“…We also noticed that the FKW remained relatively smooth at an approximately constant inclination, whereas the RKW presented random wrinkles and perturbations. With increasing AED, the keyhole penetration depth increases and the inclination of the FKW become steeper (higher FKW angle , tan~⁄ 38 ), which is attributed to higher drilling velocity 39 ( ) and increased energy coupling due to multiple reflections 8 .…”

Section: Keyhole Collapse Mechanism and Related Regime Transitionsmentioning

confidence: 99%

“…LPBF also often operates in keyhole mode melting 6 to ensure full fusion between successive layers. Additionally, laser absorptivity increases dramatically in keyhole melting due to multiple reflections of the laser beam along keyhole 8 , opening the door for fabrication of highly reflective materials (e.g., aluminium matrix composites with ~ 91% reflectivity 9 ) by LPBF, or enable a more economical laser heat source (e.g., diode laser) to be used in LPBF without sacrificing build efficiency 10 . However, the keyhole is subjected to axial fluctuations and radial perturbations 11 that are governed by the balance of energy and pressure [12][13][14] , posing a significant risk for keyhole instability 15,16 and in some cases, collapse.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Keyhole fluctuation and pore formation mechanisms during laser powder bed fusion additive manufacturing

Huang

Fleming

Clark

et al. 2021

Preprint

View full text Add to dashboard Cite

Keyhole porosity is a key concern in laser powder-bed fusion (LPBF), potentially impacting component fatigue life. However, the dynamics of keyhole porosity formation, i.e., keyhole fluctuation, collapse and bubble growth and shrinkage, remain unclear. Using synchrotron X-ray imaging we reveal keyhole and bubble behaviours, quantifying their formation mechanisms. The findings support the hypotheses that: (i) keyhole porosity can initiate not only in unstable, but also transition keyhole regimes, created by high laser power-velocity conditions, causing fast radial keyhole fluctuations (~ 10 kHz); (ii) transition regime collapse tends to occur part way up the rear-wall; and (iii) immediately after keyhole collapse, the bubble grows as pressure equilibrates then shrinks due to metal-vapour condensation. Concurrent with condensation, hydrogen diffusion into the bubble slows the shrinkage and stabilises the bubble size. The physics revealed here can guide the development of real-time monitoring and control systems for keyhole porosity.

show abstract

“…LPBF often operates in keyhole mode melting 6 to ensure complete fusion between successive layers. Additionally, laser absorptivity increases dramatically in keyhole melting due to multiple reflections of the laser beam along the keyhole 8 , opening the door for fabrication of highly reflective materials (e.g., aluminium matrix composites with ~91% reflectivity 9 ) by LPBF, or enable a more economical laser heat source (e.g., diode laser) to be used in LPBF without sacrificing build efficiency 10 . However, the keyhole is subjected to axial fluctuations and radial perturbations 11 that are governed by the balance of energy and pressure 12 – 14 , posing a significant risk for keyhole instability 15 , 16 and in some cases, collapse.…”

Section: Introductionmentioning

confidence: 99%

Keyhole fluctuation and pore formation mechanisms during laser powder bed fusion additive manufacturing

et al. 2022

View full text Add to dashboard Cite

Keyhole porosity is a key concern in laser powder-bed fusion (LPBF), potentially impacting component fatigue life. However, some keyhole porosity formation mechanisms, e.g., keyhole fluctuation, collapse and bubble growth and shrinkage, remain unclear. Using synchrotron X-ray imaging we reveal keyhole and bubble behaviour, quantifying their formation dynamics. The findings support the hypotheses that: (i) keyhole porosity can initiate not only in unstable, but also in the transition keyhole regimes created by high laser power-velocity conditions, causing fast radial keyhole fluctuations (2.5–10 kHz); (ii) transition regime collapse tends to occur part way up the rear-wall; and (iii) immediately after keyhole collapse, bubbles undergo rapid growth due to pressure equilibration, then shrink due to metal-vapour condensation. Concurrent with condensation, hydrogen diffusion into the bubble slows the shrinkage and stabilises the bubble size. The keyhole fluctuation and bubble evolution mechanisms revealed here may guide the development of control systems for minimising porosity.

show abstract

Energy-Coupling Mechanisms Revealed through Simultaneous Keyhole Depth and Absorptance Measurements during Laser-Metal Processing

Cited by 63 publications

References 56 publications

Time-Resolved Geometric Feature Tracking Elucidates Laser-Induced Keyhole Dynamics

Time-Resolved Geometric Feature Tracking Elucidates Laser-Induced Keyhole Dynamics

Keyhole fluctuation and pore formation mechanisms during laser powder bed fusion additive manufacturing

Keyhole fluctuation and pore formation mechanisms during laser powder bed fusion additive manufacturing

Contact Info

Product

Resources

About