Formation mechanisms of lack of fusion and keyhole-induced pore defects in laser powder bed fusion process: A numerical study

Yang, Xuan; Li, Yazhi; Li, Biao

doi:10.1016/j.ijthermalsci.2023.108221

Cited by 17 publications

(6 citation statements)

References 62 publications

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“…When maintaining a constant laser power of 260 W, the melt pool for both the bare plate and powder plate transitions from a keyholing mode to a conduction mode as the laser speed increases from 0.52 m/s to 2.20 m/s, shown in Figure 4(a1-e1,a2-e2). This transition is judged by the increase in the width-to-depth ratio, where the start of keyholing has typically been identified when the ratio is less than 1 [12][13][14]20,63]. This transition occurs because the decreasing laser energy deposition is insufficient to sustain the laser penetration [11][12][13]19,61].…”

Section: Melt Pool Surface Topography and Dimensions In The Single-tr...mentioning

confidence: 99%

“…Notwithstanding its advantages, LPBF presents challenges, such as the need to optimize process parameters to achieve the desired part quality and address defects during the printing process [6][7][8][9][10]; the laser-matter interaction in LPBF creates the melt pool, the fundamental element forming the desired geometrical design track by track and layer by layer and determining the quality of the builds. Insufficient melts or excessive heat input can lead to lack-of-fusion or keyholing defects [11][12][13][14][15]. The high instability introduced due to the fluid dynamics in the melt pool can cause spatters, balling, or humps that potentially affect the integrity of the materials [16][17][18][19].…”

Section: Introductionmentioning

confidence: 99%

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Understanding Melt Pool Behavior of 316L Stainless Steel in Laser Powder Bed Fusion Additive Manufacturing

Zhang,

Sun

et al. 2024

Micromachines

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In the laser powder bed fusion additive manufacturing process, the quality of fabrications is intricately tied to the laser–matter interaction, specifically the formation of the melt pool. This study experimentally examined the intricacies of melt pool characteristics and surface topography across diverse laser powers and speeds via single-track laser scanning on a bare plate and powder bed for 316L stainless steel. The results reveal that the presence of a powder layer amplifies melt pool instability and worsens irregularities due to increased laser absorption and the introduction of uneven mass from the powder. To provide a comprehensive understanding of melt pool dynamics, a high-fidelity computational model encompassing fluid dynamics, heat transfer, vaporization, and solidification was developed. It was validated against the measured melt pool dimensions and morphology, effectively predicting conduction and keyholing modes with irregular surface features. Particularly, the model explained the forming mechanisms of a defective morphology, termed swell-undercut, at high power and speed conditions, detailing the roles of recoil pressure and liquid refilling. As an application, multiple-track simulations replicate the surface features on cubic samples under two distinct process conditions, showcasing the potential of the laser–matter interaction model for process optimization.

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Section: Melt Pool Surface Topography and Dimensions In The Single-tr...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Understanding Melt Pool Behavior of 316L Stainless Steel in Laser Powder Bed Fusion Additive Manufacturing

Zhang,

Sun

et al. 2024

Micromachines

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“…Particle dimension distribution, flowability, and powder layer thickness can all have an impact on packing density and particle interaction, ultimately effecting the fusion process. Weak or inadequate bonding across layers can impair the mechanical characteristics of the printed object, resulting in decreased stiffness, strength, and fatigue resistance [134,135].…”

Section: Causes For Incomplete Fusion/bonding and Consequencesmentioning

confidence: 99%

Influence of in-situ process parameters, post heat treatment effects on microstructure and defects of additively manufactured maraging steel by laser powder bed fusion—A comprehensive review

2024

Phys. Scr.

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The laser powder bed fusion LPBF method in additive manufacturing for metals have proven to produce a final product with higher relative density, when compare to other metal additive manufacturing processes like WAAM, DED and it takes less time even for complex designs. Despite the use of many metal-based raw materials in the LPBF method for production of products. Maraging steel (martensitic steel) is used in aeronautical and aircraft applications in view of its advantages including low weight, high strength, long-term corrosion resistance, low cost, availability, and recyclability. A research gap concerns the selection of design, dimension, accuracy, process parameters according to different grades, and unawareness of various maraging steels other than specific maraging steels. In this comprehensive review, the research paper provides information about on LPBF maraging steel grades, their process parameters and defects, microstructure characteristics, heat treatments, and the resulting mechanical characteristics changes. In addition, detailed information about the aging properties, fatigue, residual and future scope of different maraging steel grades in LPBF for various applications are discussed.

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“…Meanwhile, Lu Wang et al [ 85 ] used a coupled multi-physical field model including heat transfer, liquid flow, metal vaporization, margin effect, and Darcy’s law for numerical simulation, mainly simulating the velocity field and temperature field of the melt pool, etc., while using high-speed X-ray imaging for experimental verification, and found that the uneven distribution of recoil pressure on the surface of the keyhole increases the formation of keyhole pores; in addition, different process parameters also affect the formation of keyholes, while low ambient pressure can reduce or even eliminate the formation of keyhole pores, and the instability of the keyhole leads to the formation process of pores, as shown in Figure 11 . In addition to the numerical simulation analyses of the melt pool by the above scholars, other scholars have also conducted related studies [ 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 ], where scholars have mainly focused on the process of keyhole generation, the influence of process parameters and processing atmosphere on the melt pool morphology, and the relationship between the unstable state of the melt pool and part defects. At the same time, a multi-physics field coupling model was established to simulate the process of laser and metal powder interaction in a more realistic way.…”

Section: Mechanism Of Metal Evaporation In the Lpbf Processmentioning

confidence: 99%

Review of Visual Measurement Methods for Metal Vaporization Processes in Laser Powder Bed Fusion

et al. 2023

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Laser powder bed fusion (LPBF) is of great importance for the visual measurement and analysis of the metallization process, which is the process of solid, liquid, and gas phase transformations of metal powders under high-energy laser irradiation due to the low boiling point/high saturated vapor pressure. Since the evaporation of metals involves the interaction of driving forces such as vapor back pressure, surface tension, and gravity, the movement of the melt pool is not stable. At the same time, it also produces vaporization products such as vapor plumes and sprays, which cause defects such as bubbles, porosity, lack of fusion, inclusions, etc., during the manufacturing process of the parts, affecting the performance and manufacturing quality of the parts. More and more researchers are using imaging technologies, such as high-speed X-ray, high-speed visible light cameras, and high-speed schlieren imaging, to perform noncontact visual measurements and analyses of the melt pool, vapor plume, and spatter during the metal evaporation process, and the results show that the metal evaporation process can be suppressed by optimizing the process parameters and changing the processing atmosphere, thereby reducing part defects and improving part performance and built part quality. This paper reviews the research on metal evaporation mechanisms and visual measurement methods of metal evaporation, then discusses the measures of metal evaporation, and finally summarizes and prospects the future research hotspots of LPBF technology, according to the existing scholars’ research on numerical simulation analysis and visual measurement methods of the metal evaporation process.

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Formation mechanisms of lack of fusion and keyhole-induced pore defects in laser powder bed fusion process: A numerical study

Cited by 17 publications

References 62 publications

Understanding Melt Pool Behavior of 316L Stainless Steel in Laser Powder Bed Fusion Additive Manufacturing

Understanding Melt Pool Behavior of 316L Stainless Steel in Laser Powder Bed Fusion Additive Manufacturing

Influence of in-situ process parameters, post heat treatment effects on microstructure and defects of additively manufactured maraging steel by laser powder bed fusion—A comprehensive review

Review of Visual Measurement Methods for Metal Vaporization Processes in Laser Powder Bed Fusion

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