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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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Investigation of cut quality in fiber laser cutting of CFRP
摘要： Fiber laser cutting of CFRP sheets was investigated using a 2 kW multi-mode fiber laser, focusing on how the cut quality factors, such as kerf width, kerf depth, matrix evaporation width, matrix recession width, kerf taper angle, matrix damage zone, and cut surface morphology, change as laser power, laser scanning speed, and the number of laser passes are varied. By designing a systematic experiment on a large process window, several important parameters for kerf width, kerf depth, matrix evaporation width, and matrix recession width were identified, and using them, it was verified that the beam scanning speed is a dominant factor for minimizing thermal damages. Also, circular rings were observed in each carbon fiber at the cut surfaces, and it looked as if they were generated when each fiber was thermally fused in the radial direction. A larger number of laser passes was found to contribute to a smooth surface morphology, because of the formation of highly-fused surfaces, which prevents fiber delamination and pull-outs. Optimum process conditions were also identified by comparing various cut quality factors.
关键词： Fiber laser cutting,Optimal process conditions,Cut quality factors,Thermal damage,Carbon fiber reinforced plastic (CFRP)
更新于2025-11-28 14:24:20
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Effect of shielding gas flow on welding process of laser-arc hybrid welding and MIG welding
摘要： The influence of shielding gas on welding process of laser-arc hybrid welding (LAHW) and metal inert-gas welding (MIG) was investigated by the computational fluid dynamics analysis (CFD) and high-speed photography. The results show that the process stability of MIG under high gas flow rate is poorer than that of LAHW. And the force of gas flow Fg can hinder the droplet transfer, whether MIG or LAHW. But the vaporization-induced recoil force Fv in LAHW helps to reduce this kind of hindrance and keep the process stability. Next, it can be found that the shielded gas flow mode in the main welding area cannot be changed significantly by increasing the shielding gas flow rate, while high gas flow rate can increase the area of high argon concentration and benefit the spread of molten metal.
关键词： Welding process,Computational fluid dynamics analysis,Laser-arc hybrid welding,MIG welding
更新于2025-11-28 14:24:20
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Process control and quality assurance in remote laser beam welding by optical coherence tomography
摘要： Remote laser beam welding significantly outperforms conventional joining techniques in terms of flexibility and productivity. This process benefits in particular from a highly focused laser radiation and thus from a well-defined heat input. The small spot sizes of high brilliance laser beam sources, however, require a highly dynamic and precise positioning of the beam. Also, the laser intensities typically applied in this context result in high process dynamics and in demand for a method to ensure a sufficient weld quality. A novel sensor concept for remote laser processing based on optical coherence tomography (OCT) was used for both quality assurance and edge tracking. The OCT sensor was integrated into a 3D scanner head equipped with an additional internal scanner to deflect the measuring beam independently of the processing beam. With this system, the surface topography of the process zone as well as the surrounding area can be recorded. Fundamental investigations on aluminum, copper, and galvanized steel were carried out. Initially, the influence of the material, the angle of incidence, the welding position within the scanning field, and the temperature on the OCT measuring signal were evaluated. Based on this, measuring strategies for edge tracking were developed and validated. It was shown that orthogonal measuring lines in the advance of the process zone can reliably track the edge of a fillet weld. By recording the topography in the trailing area of the process zone, it was possible to assess the weld seam quality. Comparing the results to microscopic measurements, it was shown that the system is capable of clearly identifying characteristic features of the weld seam. Also, it was possible to observe an influence of the welding process on the surface properties in the heat-affected zone, based on the quality of the measuring signal.
关键词： inline quality assurance,optical coherence tomography,remote laser beam welding,process control
更新于2025-11-28 14:24:20
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Crystalline phase effect on the up-conversion processes and white emission of Yb3+/Er3+/Tm3+: Y2Si2O7 nanocrystals.
摘要： Yb3+, Er3+, Tm3+: Y2Si2O7 nano powders were fabricated by sol-gel method and then annealed at two different temperatures of 1050°C and 1480°C for 12 h to investigate the phase effect on the structural and optical properties. X-ray diffraction patterns (XRD) of all powders revealed that most of the peaks were in good harmony with the standard JCPDS cards of Y2Si2O7 (PDF#38-0223 and PDF#38-0440). SEM images of the powders were taken to examine the morphology and chemical analysis of the powders. Diffuse reflections spectra of Y2Si2O7 exhibited varying number of transitions depending on the dopant ion in all powders in the range of 400-1050 nm. Spectral properties of the powders were detailed to identify the possible up-conversion (UC) emission mechanism in the range between 400 - 900 nm under 975 nm excitation. The broadening white light emission was observed with increasing laser pumping power at room temperature as well. Spectral profiles of the transitions observed in both reflectance and up-conversion luminescence spectra were found to be crystalline phase depended.
关键词： Nanophosphors,Sol–gel process,Up-conversion,White emission
更新于2025-11-25 10:30:42
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Color Reproduction Accuracy Promotion of 3D-Printed Surfaces Based on Microscopic Image Analysis
摘要： Full-color 3D printing technology is a powerful process to manufacture intelligent customized colorful objects with improved surface qualities; however, poor surface color optimization methods are the main impeding factors for its commercialization. As such, the paper explored the correlation between microstructure and color reproduction, then an assessment and prediction method of color optimization based on microscopic image analysis was proposed. The experimental models were divided into 24-color plates and 4-color cubes printed by ProJet 860 3D printer, then impregnated according to preset parameters, at last measured by a spectrophotometer and observed using both a digital microscope and a scanning electron microscope. The results revealed that the samples manifested higher saturation and smaller chromatic aberration (ΔE) after post-processing. Moreover, the brightness of the same color surface increased with the increasing soaked surface roughness. Further, reduction in surface roughness, impregnation into surface pores, and enhancement of coating transparency effectively improved the accuracy of color reproduction, which could be verified by the measured values. Finally, the chromatic aberration caused by positioning errors on different faces of the samples was optimized, and the value of ΔE for a black cube was reduced from 8.12 to 0.82, which is undetectable to human eyes.
关键词： Structural characterisation,Impregnating process,Scanning electron microscope,Image analysis,Color optimization,Full-color printing
更新于2025-11-21 11:18:25
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Spectroscopic monitoring of laser blown powder directed energy deposition of Alloy 718
摘要： Experimental explorations of a spectrometer system used for in-process monitoring of the laser blown powder directed energy deposition of Alloy 718 is presented. Additive manufacturing of metals using this laser process experiences repeated heating and cooling cycles which will influence the final microstructure and chemical composition at every given point in the built. The spectrometer system disclosed, under certain process conditions, spectral lines that indicate vaporisation of chromium. Post process scanning electron microscope energy dispersive spectroscopy analysis of the deposited beads confirmed a reduction of chromium. Since the chromium concentration in Alloy 718 is correlated to corrosion resistance, this result encourages to further investigations including corrosion tests.
关键词： additive manufacturing,laser blown powder directed energy deposition,spectroscopic system,in-process monitoring
更新于2025-11-21 11:01:37
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Sol-gel processed vanadium oxide as efficient hole injection layer in visible and ultraviolet organic light-emitting diodes
摘要： Low-cost, high-throughput and scalable production currently boosts organic electronic device towards solution processing. Sol-gel processed aqueous vanadium oxide (h-VOx) is facilely synthesized and proven to be efficient hole injection layer (HIL) in visible and ultraviolet organic light-emitting diodes (OLEDs). Atomic force microscopy and X-ray/ultraviolet photoelectron spectroscopy measurements indicate that h-VOx behaves superior film morphology and exceptional electronic properties such as oxygen vacancy dominated non-stoichiometry and appropriate surface work function. With tris(8-hydroxy-quinolinato)aluminium as emitter, the visible OLED gives maximum luminous and power efficiencies of 6.3 cd/A and 3.2 lm/W, respectively, which are slightly superior to the counterpart with vacuum thermally-evaporated VOx (5.6 cd/A and 2.7 lm/W). With 3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole as emitter, the ultraviolet OLED produces attractive short-wavelength emission of 379 nm with full width at half maximum of 40 nm and improved durability. The maximum radiance and external quantum efficiency reach 15.3 mW/cm2 and 2.92%, respectively, which are considerably enhanced in comparison with the corresponding reference (11.9 mW/cm2 and 2.32%). Current versus voltage characteristics and impedance spectroscopy analysis elucidate that h-VOx exhibits robust hole injection and accordingly high-performance OLEDs. Our results pave an alternative way for advancing organic electronic devices and VOx applications with solution process.
关键词： Organic light-emitting diode,Hole injection,Solution process,Vanadium oxide,Sol-gel method
更新于2025-11-20 15:33:11
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Light-Stimulated Synaptic Transistors Fabricated by a Facile Solution Process Based on Inorganic Perovskite Quantum Dots and Organic Semiconductors
摘要： Implementation of artificial intelligent systems with light-stimulated synaptic emulators may enhance computational speed by providing devices with high bandwidth, low power computation requirements, and low crosstalk. One of the key challenges is to develop light-stimulated devices that can response to light signals in a neuron-/synapse-like fashion. A simple and effective solution process to fabricate light-stimulated synaptic transistors (LSSTs) based on inorganic halide perovskite quantum dots (IHP QDs) and organic semiconductors (OSCs) is reported. Blending IHP QDs and OSCs not only improves the charge separation efficiency of the photoexcited charges, but also induces delayed decay of the photocurrent in the IHP QDs/OSCs hybrid film. The enhanced charge separation efficiency results in high photoresponsivity, while the induced delayed decay of the photocurrent is critical to achieving light-stimulating devices with a memory effect, which are important for achieving high synaptic performance. The LSSTs can respond to light signals in a highly neuron-/synapse-like fashion. Both short-term and long-term synaptic behaviors have been realized, which may lay the foundation for the future implementation of artificial intelligent systems that are enabled by light signals. More significantly, LSSTs are fabricated by a facile solution process which can be easily applied to large-scale samples.
关键词： light-stimulated synaptic transistors,solution process,organic semiconductors,blended materials,inorganic halide perovskite quantum dots
更新于2025-11-19 16:56:42
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Improvement of Ga distribution with Sb incorporation for two-step low-temperature processing of CIGSe thin film solar cells
摘要： In this study, the application of Sb incorporation for low-temperature (≤ 450 °C) processing of Cu(In,Ga)Se2 (CIGSe) solar cells is explored. At low reaction temperature, most Ga remains at the back of the ?lm adjacent to the Mo back contact. We observed that the incorporated Sb enhanced grain size and improved device performance compared with similarly processed CIGSe ?lms made without Sb. From the energy-dispersive spectroscopy analysis and secondary ion mass spectrometry results, it was determined that elemental Ga accumulation at the back of the reacted ?lm after the two-step selenization process was signi?cantly alleviated owing to Sb incorporation. Signi?cant Sb-induced grain size enhancement was con?rmed using cross-sectional scanning electron microscopy. The electronic and optical properties of the Sb incorporated CIGSe ?lms were examined with admittance spectroscopy and ?uorescence lifetime imaging techniques.
关键词： Ga distribution,Thin ?lm solar cell,Sb incorporation,Low temperature process
更新于2025-11-14 17:28:48