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A statistical learning method for image-based monitoring of the plume signature in laser powder bed fusion
摘要： The industrial breakthrough of metal additive manufacturing processes mainly involves highly regulated sectors, e.g., aerospace and healthcare, where both part and process qualification are of paramount importance. Because of this, there is an increasing interest for in-situ monitoring tools able to detect process defects and unstable states since their onset stage during the process itself. In-situ measured quantities can be regarded as “signatures” of the process behaviour and proxies of the final part quality. This study relies on the idea that the by-products of laser powder bed fusion (LPBF) can be used as process signatures to design and implement statistical monitoring methods. In particular, this paper proposes a methodology to monitor the LPBF process via in-situ infrared (IR) video imaging of the plume formed by material evaporation and heating of the surrounding gas. The aspect of the plume naturally changes from one frame to another following the natural dynamics of the process: this yields a multimodal pattern of the plume descriptors that limits the effectiveness of traditional statistical monitoring techniques. To cope with this, a nonparametric control charting scheme is proposed, called K-chart, which allows adapting the alarm threshold to the dynamically varying patterns of the monitored data. A real case study in LPBF of zinc powder is presented to demonstrate the capability of detecting the onset of unstable conditions in the presence of a material that, despite being particularly interesting for biomedical applications, imposes quality challenges in LPBF because of its low melting and boiling points. A comparison analysis is presented to highlight the benefits provided by the proposed approach against competitor methods.
关键词： Process plume,Metal additive manufacturing,Laser powder bed fusion,Infrared imaging,In-situ monitoring,Zinc
更新于2025-11-28 14:24:20
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Laser additive manufacturing of biodegradable magnesium alloy WE43: a detailed microstructure analysis
摘要： WE43, a magnesium alloy containing yttrium and neodymium as main alloying elements, has become a well-established bioresorbable implant material. Implants made of WE43 are often fabricated by powder extrusion and subsequent machining, but for more complex geometries laser powder bed fusion (LPBF) appears to be a promising alternative. However, the extremely high cooling rates and subsequent heat treatment after solidification of the melt pool involved in this process induce a drastic change in microstructure, which governs mechanical properties and degradation behaviour in a way that is still unclear. In this study we investigated the changes in the microstructure of WE43 induced by LPBF in comparison to that of cast WE43. We did this mainly by electron microscopy imaging, and chemical mapping based on energy-dispersive X-ray spectroscopy in conjunction with electron diffraction for the identification of the various phases. We identified different types of microstructure: an equiaxed grain zone in the center of the laser-induced melt pool, and a lamellar zone and a partially melted zone at its border. The lamellar zone presents dendritic lamellae lying on the Mg basal plane and separated by aligned Nd-rich nanometric intermetallic phases. They appear as globular particles made of Mg3Nd and as platelets made of Mg41Nd5 occurring on Mg prismatic planes. Yttrium is found in solid solution and in oxide particles stemming from the powder particles’ shell. Due to the heat influence on the lamellar zone during subsequent laser passes, a strong texture developed in the bulk material after substantial grain growth.
关键词： Rapid solidification,Microstructure,Bone scaffolds,Electron microscopy,Biodegradable implants,WE43,Laser powder bed fusion,Magnesium
更新于2025-11-21 11:20:48
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Rapid Alloy Development of Extremely High-Alloyed Metals Using Powder Blends in Laser Powder Bed Fusion
摘要： The design of new alloys by and for metal additive manufacturing (AM) is an emerging field of research. Currently, pre-alloyed powders are used in metal AM, which are expensive and inflexible in terms of varying chemical composition. The present study describes the adaption of rapid alloy development in laser powder bed fusion (LPBF) by using elemental powder blends. This enables an agile and resource-efficient approach to designing and screening new alloys through fast generation of alloys with varying chemical compositions. This method was evaluated on the new and chemically complex materials group of multi-principal element alloys (MPEAs), also known as high-entropy alloys (HEAs). MPEAs constitute ideal candidates for the introduced methodology due to the large space for possible alloys. First, process parameters for LPBF with powder blends containing at least five different elemental powders were developed. Secondly, the influence of processing parameters and the resulting energy density input on the homogeneity of the manufactured parts were investigated. Microstructural characterization was carried out by optical microscopy, electron backscatter diffraction (EBSD), and energy-dispersive X-ray spectroscopy (EDS), while mechanical properties were evaluated using tensile testing. Finally, the applicability of powder blends in LPBF was demonstrated through the manufacture of geometrically complex lattice structures with energy absorption functionality.
关键词： multi-principal element alloys,high-entropy alloys,additive manufacturing,rapid alloy development,powder blends,laser powder bed fusion
更新于2025-11-21 11:01:37
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Direct observation of pore formation mechanisms during LPBF additive manufacturing process and high energy density laser welding
摘要： Laser powder bed fusion (LPBF) is a 3D printing technology that can print parts with complex geometries that are unachievable by conventional manufacturing technologies. However, pores formed during the printing process impair the mechanical performance of the printed parts, severely hindering their widespread application. Here, we report six pore formation mechanisms that were observed during the LPBF process. Our results reconfirm three pore formation mechanisms - keyhole induced pores, pore formation from feedstock powder and pore formation along the melting boundary during laser melting from vaporization of a volatile substance or an expansion of a tiny trapped gas. We also observe three new pore formation mechanisms: (1) pore trapped by surface fluctuation, (2) pore formation due to depression zone fluctuation when the depression zone is shallow and (3) pore formation from a crack. The results presented here provide direct evidence and insight into pore formation mechanisms during the LPBF process, which may guide the development of pore elimination/mitigation approaches. Since certain laser processing conditions studied here are similar to the situations in high energy density laser welding, the results presented here also have implications for laser welding.
关键词： Pore formation,Laser powder bed fusion,X-ray imaging,Laser welding,Additive manufacturing
更新于2025-09-23 15:21:01
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Correlations between thermal history and keyhole porosity in laser powder bed fusion
摘要： Additive manufacturing has the potential to revolutionize the production of metallic components as it yields near net shape parts with complex geometries and minimizes waste. At the present day, additively manufactured components face qualification and certification challenges due to the difficulty in controlling defects. This has driven a significant research effort aimed at better understanding and improving processing controls – yielding a plethora of in-situ measurements aimed at correlating defects with material quality metrics of interest. In this work, we develop machine-learning methods to learn correlations between thermal history and subsurface porosity for a variety of print conditions in laser powder bed fusion. Un-normalized surface temperatures (in the form of black-body radiances) are obtained using high-speed infrared imaging and porosity formation is observed in the sample cross-section through synchrotron x-ray imaging. To demonstrate the predictive power of these features, we present four statistical machine-learning models that correlate temperature histories to subsurface porosity formation in laser fused Ti-6Al-4V powder.
关键词： in-situ measurement,keyhole porosity,machine learning,laser powder bed fusion,x-ray imaging
更新于2025-09-23 15:21:01
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[IEEE NAECON 2019 - IEEE National Aerospace and Electronics Conference - Dayton, OH, USA (2019.7.15-2019.7.19)] 2019 IEEE National Aerospace and Electronics Conference (NAECON) - In Situ Process Monitoring for Laser-Powder Bed Fusion using Convolutional Neural Networks and Infrared Tomography
摘要： Additive Manufacturing (AM) is a growing field for various industries of avionics, biomedical, automotive and manufacturing. The onset of Laser Powder Bed Fusion (LPBF) technologies for metal printing has shown exceptional growth in the past 15 years. Quality of parts for LPBF is a concern for the industry, as many parts produced are high risk, such as biomedical implants. To address these needs, a LPBF machine was designed with in-situ sensors to monitor the build process. Image processing and machine learning algorithms provide an efficient means to take bulk data and assess part quality, validating specific internal geometries and build defects. This research will analyze infrared (IR) images from a Selective Laser Melting (SLM) machine using a Computer Aided Design (CAD) designed part, featuring specific geometries (squares, circles, and triangles) of varying sizes (0.75-3.5 mm) on multiple layers for feature detection. Applying image processing to denoise, then Principal Component Analysis (PCA) for further denoising and applying Convolution Neural Networks (CNN) to identify the features and identifying a class which does not belong to a dataset, where a dataset are created from CAD images. Through this automated process, 300 geometric elements detected, classified, and validated against the build file through CNN. In addition, several build anomalies were detected and saved for end-user inspection.
关键词： Laser Powder Bed Fusion (LPBF),Principal Component Analysis (PCA),infrared image (IR),Convolution Neural Networks (CNN),Additive Manufacturing (AM),Computer Aided Design (CAD)
更新于2025-09-23 15:21:01
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The Average Grain Size and Grain Aspect Ratio in Metal Laser Powder Bed Fusion: Modeling and Experiment
摘要： The additive manufacturing (AM) process induces high uncertainty in the mechanical properties of 3D-printed parts, which represents one of the main barriers for a wider AM processes adoption. To address this problem, a new time-efficient microstructure prediction algorithm was proposed in this study for the laser powder bed fusion (LPBF) process. Based on a combination of the melt pool modeling and the design of experiment approaches, this algorithm was used to predict the microstructure (grain size/aspect ratio) of materials processed by an EOS M280 LPBF system, including Iron and IN625 alloys. This approach was successfully validated using experimental and literature data, thus demonstrating its potential efficiency for the optimization of different LPBF powders and systems.
关键词： laser powder bed fusion,additive manufacturing,microstructure,process optimization,analytical model
更新于2025-09-23 15:21:01
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A review of technological improvements in laser-based powder bed fusion of metal printers
摘要： Additive manufacturing (AM) is an emerging process that has been extremely improved in terms of technology and application in recent years. In this technology review, new industrial improvements in laser powder bed fusion (LPBF) of metals are discussed. LPBF has the lowest build rate among all AM processes that produce metals such as electron beam powder bed fusion, direct energy deposition, binder jetting and sheet lamination. The findings of the current research show that the most innovations and future directions of LPBF printers are toward increasing the speed of the process by using interchangeable feedstock chamber, closed-loop control powder handling, automated powder sieving, multi-layer concurrent printing, 2-axis coating and multi powder hoppers. To increase the speed of the process, the new improvements for transferring time and using fast lasers are presented. Another innovation in the building of LPBF printers is enhancing part quality by improving lasers with the shorter beam diameter, multi-lasers, uniform inert gas flow, accurate positioning systems, using high vacuum systems and using sensors and automation.
关键词： Industrial improvement,Additive manufacturing,Laser,Powder bed fusion
更新于2025-09-23 15:21:01
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Connecting Diffraction-Based Strain with Macroscopic Stresses in Laser Powder Bed Fused Ti-6Al-4V
摘要： The laser powder bed fusion (LPBF) production process often results in large residual stress (RS) in the parts. Nondestructive techniques to determine RS are badly needed. However, a reliable quantification of macro-RS (i.e., stress at the component level) by means of diffraction-based techniques is still a great challenge, because the link between diffraction-based strain and macro-RS is not trivial. In this study, we experimentally determine (by means of in-situ synchrotron radiation diffraction) this link for LPBF Ti-6Al-4V. We compare our results with commonly used models to determine the so-called diffraction elastic constants (DECs). We show that LPBF materials possess different DECs than wrought alloys, simply because their microstructural and mechanical properties are different. We also show that the existing models can be used to calculate DECs only if high accuracy of the RS values is not required. If the peculiarities of the microstructure have to be taken into account (as is the case of additively manufactured materials), a radically new approach is desirable.
关键词： synchrotron radiation diffraction,Laser powder bed fusion,residual stress,Ti-6Al-4V,diffraction elastic constants
更新于2025-09-23 15:21:01
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Computational Assessment of Thermokinetics and Associated Microstructural Evolution in Laser Powder Bed Fusion Manufacturing of Ti6Al4V Alloy
摘要： Although most of the near non-equilibrium microstructures of alloys produced by laser powder bed fusion (LPBF) additive manufacturing (AM) are being reported at a rapid rate, the accountable thermokinetics of the entire process have rarely been studied. In order to exploit the versatility of this AM process for the desired properties of built material, it is crucial to understand the thermokinetics associated with the process. In light of this, a three-dimensional thermokinetic model based on the finite element method was developed to correlate with the microstructure evolved in additively manufactured Ti6Al4V alloy. The computational model yielded the thermal patterns experienced at given location while building a single layer through multiple laser scans and a whole part through multiple layers above it. X-ray analysis of the resultant microstructure confirmed the presence of acicular martensitic (α′) phase of (002) texture within the build-plane. Computationally predicted magnitude of the thermal gradients within the additively manufactured Ti6Al4V alloy in different directions (X, Y, and Z) facilitated the understanding about the evolution of grain morphology and orientation of acicular martensite in prior β grains. The scanning electron microscopy observations of the alloy revealed the distinct morphology of phase precipitated within the martensitic phase, whose existence was, in turn, understood through predicted thermal history.
关键词： Thermokinetics,Additive manufacturing,Microstructural evolution,Laser powder bed fusion,Ti6Al4V alloy
更新于2025-09-23 15:21:01