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Experimental investigation on a new hybrid laser process for surface structuring by vapor pressure on Ti6Al4V
摘要： Besides conventional structuring processes such as turning, milling or photo-chemical etching, laser processes are increasingly being used for surface structuring of metals. These laser processes differ fundamentally in that structuring is carried out either by material removal or by material redistribution. In this study, a new hybrid process of material ablation by means of pulsed laser radiation and material redistribution based on a remelting process by means of cw laser radiation is experimentally investigated. Besides an introduction to this new hybrid process, we give a detailed description of the equipment and methods used as well as surface structures produced on Ti6Al4V. A melt pool was generated on a prepared Ti6Al4V surface using cw laser radiation with a laser beam diameter of 520 μm, laser power of 220 W, and a scanning velocity of 100 mm/s. In order to create surface structures, simultaneously, superimposed pulsed laser radiation with a laser beam diameter of 65 μm, pulse duration of 60 ns, a maximum pulse energy of 0.35 mJ, and a pulse frequency of 50 kHz was used to evaporate small amounts of molten material from the melt pool. This localized evaporation of molten material is assumed to create vapor pressure that deforms the melt pool surface and therefore leads to surface structures. Our results indicate that by pulsed laser radiation capillary surface waves with a wavelength of the doubled laser beam diameter are excited on the melt pool surface. This forced excitation of capillary surface waves result in surface structures that are analyzed after solidification by means of white light interferometry. Based on this analysis we derived an oscillation frequency of ν = 2.27 (± 0.16) kHz for the excited capillary surface wave as well as an effective kinematic viscosity of μ = 0.1328 cm2 s-1 for the damping of this surface oscillation during solidification. In terms of structural features, we achieved surface structures with heights of up to 100 μm. Furthermore, structure height controllably scales in dependence on pulse energy and number of laser pulses as long as no ejection of molten material takes place. Finally, a comparison of the redistributed material volume per time shows that we achieved a volume redistribution rate of 28.37 mm3/min, which is significantly bigger than has been achieved with other laser texturing techniques so far and demonstrates the high potential of this new hybrid technique not only for surface structuring purposes.
关键词： surface structuring,melt pool,material redistribution,capillary surface wave,Ti6Al4V,remelting
更新于2025-09-16 10:30:52
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Topographic Measurement of Individual Laser Tracks in Alloy 625 Bare Plates
摘要： Additive manufacturing (AM) combines all of the complexities of materials processing and manufacturing into a single process. The digital revolution made this combination possible, but the commercial viability of these technologies for critical parts may depend on digital process simulations to guide process development, product design, and part qualification. For laser powder bed fusion, one must be able to model the behavior of a melt pool produced by a laser moving at a constant velocity over a smooth bare metal surface before taking on the additional complexities of this process. To provide data on this behavior for model evaluations, samples of a single-phase nickel-based alloy were polished smooth and exposed to a laser beam at three different power and speed settings in the National Institute of Standards and Technology Additive Manufacturing Metrology Testbed and a commercial AM machine. The solidified track remaining in the metal surface after the passing of the laser is a physical record of the position of the air–liquid–solid interface of the melt pool trailing behind the laser. The surface topography of these tracks was measured and quantified using confocal laser scanning microscopy for use as benchmarks in AM model development and validation. These measurements are part of the Additive Manufacturing Benchmark Test Series.
关键词： Additive manufacturing,Welding,Nickel-based superalloys,Topography data,Laser melt pool,Metals
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE 15th International Conference on Automation Science and Engineering (CASE) - Vancouver, BC, Canada (2019.8.22-2019.8.26)] 2019 IEEE 15th International Conference on Automation Science and Engineering (CASE) - Iterative learning control for power profile shaping in selective laser melting
摘要： Selective laser melting (SLM) can be used to manufacture functional metal parts with complex geometries that cannot be produced by traditional manufacturing methods. However, SLM process control cannot yet guarantee the end part quality required for critical applications. The application of model-based control strategies to SLM is complicated by both the closed architecture of industrial SLM machines and the lack of suitable control-oriented process models. In this paper we (1) present an open-source SLM printer that allows implementation of the on-the-fly power adjustment and (2) use a data-driven method, iterative learning control (ILC) to learn the suitable laser power profile using the melt pool emission measurements from a coaxial camera. We demonstrate the effectiveness of the proposed ILC approach through experiments on the open-source SLM machine.
关键词： iterative learning control,laser power profile,open-source SLM printer,Selective laser melting,melt pool emission measurements
更新于2025-09-12 10:27:22
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Melt pool monitoring for laser beam melting of metals: inline-evaluation and remelting of surfaces
摘要： Laser Beam Melting of Metals (LBM-M) is an additive manufacturing technique that is applied successfully for the production of complex parts, small batch series and prototypes. In LBM metallic parts are generated layer by layer directly from sliced CAD data. For each layer a thin powder layer is deposited and subsequently irradiated by a focused laser beam which is guided by a galvanometer scanner. Due to variations in the powder stock, plain parameter sets and unresolved machine maturity problems, quality fluctuations are a major problem for a future series production. Surface roughness of parts during manufacturing is a quality issue. In this paper, we address it with a coaxial melt pool monitoring system and show a method for inline evaluation of surfaces by means of melt pool monitoring and the results of applied remelting strategies.
关键词： Laser Beam Melting,Additive Manufacturing,process stability,remelting,Selective Laser Melting,Melt pool Monitoring,Surface roughness,quality assurance
更新于2025-09-12 10:27:22
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Melt pool monitoring for laser beam melting of metals: assistance for material qualification for the stainless steel 1.4057
摘要： Laser Beam Melting of Metals (LBM-M) is an additive manufacturing technique that is successfully applied for the manufacturing of complex parts, small batch series and prototypes. In LBM metallic parts are generated layer by layer directly from sliced CAD data. For each layer a thin powder layer is deposited and subsequently, irradiated by a focused laser beam, which is guided by a galvanometer scanner. A major drawback of this relatively new manufacturing technology is a limited material portfolio. Today, the whole procedure of material qualification is time-consuming and resource intensive because a fast and reliable modelling of the process is not yet possible. In this work we are going to show the results of a qualification procedure applying a coaxial melt pool monitoring system to determine suitable processing parameters for a material, which has not yet been processed. In this work, a stainless steel material was exemplarily used to proof the feasibility. Furthermore, we are discussing the usability of this methodology for the material qualification in LBM-M in general.
关键词： Laser Beam Melting,Additive Manufacturing,Stainless Steel,Material Qualification,Quality Assurance,Selective Laser Melting,Process Stability,Melt pool Monitoring
更新于2025-09-12 10:27:22
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Single track scanning experiment in laser powder bed fusion process
摘要： Laser powder bed fusion (LPBF) process utilizes laser source to melt the powder particles. As a result, melt pool is formed which develops along the scan track. In this study, single track scanning with Ti-6Al-4V alloy is performed in alternate layers over the supporting base pad. Multiple single scan tracks with scanning speeds of 200mm/s, 400 mm/s and 600 mm/s are defined and thermal responses are captured using infrared camera. The thermal images record the apparent temperature measurements; therefore, derivate method is used to find the liquidus-solidus transition region which is required to estimate the melt pool length and width. Based on the estimation, the average melt pool width of the single track decreased with increasing speed while the average melt pool length for 200 mm/s scanning speed was 438.62 μm, for 400 mm/s was 432.27 μm and for 600 mm/s was 451.2 μm. Besides, cylindrical powder container samples with enclosed single tracks were designed to investigate internal features using computed tomography (CT). The CT images showed that the scanning speed of 200 mm/s and 400 mm/s resulted in formation of significant number of pores due to keyhole formation which may contribute to variation in melt pool length.
关键词： Thermal image,Single track,Infrared Camera,Porosity,Melt pool
更新于2025-09-12 10:27:22
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Computational Investigation of Melt Pool Process Dynamics and Pore Formation in Laser Powder Bed Fusion
摘要： In the laser powder bed fusion additive manufacturing process, the presence of porosity may result in cracks and significantly affects the part performance. A comprehensive understanding of the melt pool process dynamics and porosity evolution can help to improve build quality. In this study, a novel multi-physics computational fluid dynamics (CFD) model has been applied to investigate the fluid dynamics in melt pools and resultant pore defects. To accurately capture the melting and solidification process, major process physics, such as the surface tension, evaporation as well as laser multi-reflection, have been considered in the model. A discrete element method is utilized to model the generation of powder spreading upon build plate by additional numerical simulations. Multiple single track experiments have been performed to obtain the melt pool shape and cross-sectional dimension information. The predicted melt pool dimensions were found to have a reasonable agreement with experimental measurements, e.g., the errors are in the range of 1.3 to 10.6% for melt pool width, while they are between 1.4 and 15.9% for melt depth. Pores are captured by both CFD simulation and x-ray computed tomography measurement for the case with a laser power of 350 W and laser speed of 100 mm/s. The formation of keyholes maybe related to the melt pool front wall angle, and it is found that the front wall angle increases with the increase in laser line energy density. In addition, a larger laser power or smaller scanning speed can help to generate keyhole-induced pores; they also contribute to produce larger sized pores.
关键词： additive manufacturing,melt pool,computational fluid dynamics (CFD),stainless steel,discrete element method (DEM),keyhole
更新于2025-09-12 10:27:22
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Melt Pool Size Control Through Multiple Closed-Loop Modalities in Laser-Wire Directed Energy Deposition of Ti-6Al-4V
摘要： Sensing and closed-loop control are critical attributes of a robust 3D printing process, such as Directed Energy Deposition (DED), in which it is necessary to manage geometry, material properties, and residual stress and distortion. The present research demonstrates multiple modes of closed-loop melt pool size control in laser-wire based DED, a form of large-scale metal additive manufacturing. First, real-time closed-loop melt pool size control through laser power modulation was demonstrated for intralayer control of bead geometry. Aspects such as controller tuning, response time, interaction with primary process variables, and disturbance rejection are presented. Next, an interlayer trend in laser power during the printing of layered components was documented, which inspired the development of novel modes of control. A controller that modulates print speed and deposition rate on a per-layer basis was developed and demonstrated, enabling the control of either average melt pool size alone or average laser power in coordination with real-time melt pool size control. This work demonstrates that accumulated heat in components under construction can be exploited to maintain process stability as print speed and deposition rate are automatically increased under closed-loop control. This has major implications for overall production efficiency. Control modes are characterized in terms of their effect on local bead geometry, global part geometry, and interlayer effect on energy density, among other factors.
关键词： Directed Energy Deposition,Monitoring,Metal,Closed-Loop,3D Printing,Ti-6Al-4V,Lasers,Control,Additive Manufacturing,Melt Pool
更新于2025-09-12 10:27:22