80 results on '"Alexander Kaplan"'
Search Results
2. The role of powder morphology in particle movement behavior in laser powder bed fusion with an emphasis on fluid drag
- Author
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Jesper Sundqvist, Alexander Kaplan, and Tatiana Fedina
- Subjects
Entrainment (hydrodynamics) ,Fusion ,Materials science ,General Chemical Engineering ,Alloy steel ,engineering.material ,Laser ,law.invention ,law ,Drag ,engineering ,Particle ,Composite material ,Pressure gradient ,Order of magnitude - Abstract
This study investigates the movement behavior of particles of dissimilar morphology in the powder bed in Laser Powder Bed Fusion. Gas atomized (GA) and water atomized (WA) low alloy steel powders were employed to study their motion around the laser scan path. Particle velocities, entrainment distances and denudation zones were measured for both powders using high-speed imaging. The entrainment of GA powder particles in front of the laser beam towards the process area was initiated 1.6 mm from the edge of the melt pool, whereas the distance was 0.6–0.8 mm for the WA powder. The differences in observed behavior were related to the variations in particle shape of the two types of powder. The processing of WA powder resulted in a 16% narrower denudation zone (for a low volumetric energy density) compared to GA powder. However, the denudation width difference decreased with increasing volumetric energy density, most likely due to a steeper pressure gradient in the process area which diminishes the impact of powder shape. X-ray computed microtomography was utilized to estimate the drag force acting on the powder particles of various morphologies. The results showed that the radial drag force exerted on GA powder was 64% greater than when using WA powder. Moreover, if the WA powder particles were of elongated shape the drag force decreased by almost an order of magnitude, demonstrating the importance of the particle's morphology in the process dynamics.
- Published
- 2022
3. Blown powder directed energy deposition on various substrate conditions
- Author
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Himani Naesstroem, Alexander Kaplan, and Frank Brueckner
- Subjects
Materials science ,Strategy and Management ,Evaporation ,Substrate (printing) ,Management Science and Operations Research ,Industrial and Manufacturing Engineering ,Galvanization ,symbols.namesake ,Cracking ,Volume (thermodynamics) ,symbols ,Deposition (phase transition) ,Wetting ,Composite material ,Porosity - Abstract
Blown powder directed energy deposition of SS316L powder is carried out on various substrate surface conditions of SS304 such as cleaned, sand blasted, milled, oily, cold galvanised and painted to study their influence on the process. High-speed imaging is used for process observation and the deposited tracks are analysed qualitatively and quantitatively using surface images, cross sectional macrographs and x-ray images. Frames from high-speed imaging reveal the removal of additional material from the substrate surface such as paint and oil. The stages involved in their removal: peeling and evaporation are presented. EDS analysis showed that no additional elements other than powder and substrate material are found in the track volume. The quantitative results for all specimens show that the surface conditions had minor influences on track width, track height, wetting angle, dilution and deposited cross sectional area. Defects such as porosity, inclusions and cracking were not observed related to the surface conditions. These findings could significantly reduce processing time by skipping the cleaning step before directed energy deposition such as laser cladding or repair in industrial applications.
- Published
- 2022
4. A pragmatic approach for assessment of laser-induced compressive residual stress profiles
- Author
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Alexander Kaplan, Handika Sandra Dewi, Philipp Krooß, Jorge Luis Arias Otero, Andreas Fischer, Joerg Volpp, David Köcher, Thomas Niendorf, Javier Souto Grela, and Jacobo Otero Tranchero
- Subjects
0209 industrial biotechnology ,Work (thermodynamics) ,Materials science ,Strategy and Management ,Context (language use) ,02 engineering and technology ,Mechanics ,Management Science and Operations Research ,021001 nanoscience & nanotechnology ,Laser ,Industrial and Manufacturing Engineering ,law.invention ,020901 industrial engineering & automation ,law ,Residual stress ,Hardening (metallurgy) ,Surface layer ,0210 nano-technology ,Material properties ,Intensity (heat transfer) - Abstract
Laser hardening is a very efficient technique for local surface treatment, however, in case of complex and large components robust processing is highly challenging due to limitations in terms of the absolute size of the overall heat-affected zone. As is shown in the present work, an increased in-depth effect can be achieved by tailoring the laser parameters without melting the surface layer. Optimization of process parameters leads to an elaborate test design demanding numerous verification measurements to determine essential material properties. In this context, the evaluation of compressive residual stress values in the surface layer is very important, e.g. in case of fatigue loaded components. However, residual stress profile measurements obtained by X-ray diffraction are very time-consuming and, thus, can significantly impair the laser parameter development cycle. For this reason, the present study introduces a novel pragmatic approach allowing for qualitative evaluation of laser-induced compressive residual stress states, in particular for multiple laser pass processes based on a Gaussian-like intensity profile. Based on straightforward analytical evaluation, several characteristic features of the affected surface layer, e.g. the position of the residual stress transition zone, can be correlated to a change of the local energy input. A novel parameter referred to as modified area energy is established in present work for this purpose. This novel energy approach provides for an essential contribution to the field of laser hardening to considerably shorten the experimental effort within the laser parameter search.
- Published
- 2021
5. Single-Subject TMS Pulse Visualization on MRI-Based Brain Model: A precise method for mapping TMS pulses on cortical surface
- Author
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Nikolay Syrov, Alfiia Mustafina, Artemiy Berkmush-Antipova, Lev Yakovlev, Andrey Demchinsky, Daria Petrova, and Alexander Kaplan
- Subjects
Medical Laboratory Technology ,Clinical Biochemistry - Published
- 2023
6. Vertical laser metal wire deposition of Al-Si alloys
- Author
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Joerg Volpp, Alexander Kaplan, Sicong Wang, and Adrien Da Silva
- Subjects
0209 industrial biotechnology ,Materials science ,Metallurgy ,chemistry.chemical_element ,02 engineering and technology ,Solidus ,Liquidus ,010501 environmental sciences ,Thermal conduction ,Laser ,01 natural sciences ,law.invention ,Metal ,020901 industrial engineering & automation ,chemistry ,Aluminium ,law ,visual_art ,visual_art.visual_art_medium ,General Earth and Planetary Sciences ,Deposition (phase transition) ,Layer (electronics) ,0105 earth and related environmental sciences ,General Environmental Science - Abstract
Additive Manufacturing of aluminium alloys has become crucial for lightweight applications. However, new materials and techniques need to be developed in order to achieve more advanced properties and higher efficiency. Therefore, a new energy-efficient wire deposition strategy was developed for processing aluminium-silicon alloys with Laser Metal Wire Deposition. Three alloys with different Si-contents were studied: AlSi5, AlSi10Mg and AlSi12. Different thicknesses of partially melted zones were observed and explained. The previous layer was partly remelted only by the heat conduction in the melt pool. It was found that the thickness of the partially melted zone depends on the difference of temperature between the liquidus and solidus.
- Published
- 2020
7. The stability of laser welding with an off-axis wire feed
- Author
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Alexander Kaplan, Himani Siva Prasad, and Jan Frostevarg
- Subjects
0209 industrial biotechnology ,Materials science ,business.industry ,Metals and Alloys ,Process (computing) ,Streak ,Laser beam welding ,02 engineering and technology ,Welding ,Industrial and Manufacturing Engineering ,Computer Science Applications ,law.invention ,020303 mechanical engineering & transports ,020901 industrial engineering & automation ,Optics ,0203 mechanical engineering ,law ,Position (vector) ,Robustness (computer science) ,Modeling and Simulation ,Ceramics and Composites ,Undercut ,business ,Joint (geology) - Abstract
The concept using an off-axis filler wire during laser welding is introduced here in order to provide added process robustness considering gap width variations. Its stability is investigated with respect to gap width, welding speeds and powers. Geometry of the welds is analysed by tracing of weld cap edges and joint cross sections, connecting trends to weld parameters. High speed imaging and streak images are used to further study and describe sequences of events, including undercut formation. Formation of imperfections are found to be mainly correlated to wire feed position variations at the surface due to irregular melting of the wire tip.
- Published
- 2019
8. Microstructure morphology characterization of welding consumables studied by pulse-shaped laser heating
- Author
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Alexander Kaplan, Anandkumar Ramasamy, Bert Kalfsbeek, Stephanie M. Robertson, Joerg Volpp, and Jan Frostevarg
- Subjects
0209 industrial biotechnology ,Toughness ,Consumables ,Materials science ,02 engineering and technology ,Welding ,Microstructure ,Industrial and Manufacturing Engineering ,Pulse (physics) ,law.invention ,Characterization (materials science) ,020303 mechanical engineering & transports ,020901 industrial engineering & automation ,0203 mechanical engineering ,Artificial Intelligence ,law ,Microstructure morphology ,Laser heating ,Composite material - Abstract
During welding, wire consumables can essentially contribute to the resulting microstructures and mechanical properties. In order to maintain high toughness even for high strength steel, certain mic ...
- Published
- 2019
9. Sensitisation behaviour of drop-deposited 11% Cr ferritic stainless steel
- Author
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Jesper Sundqvist and Alexander Kaplan
- Subjects
010302 applied physics ,Materials science ,Drop (liquid) ,Metallurgy ,Alloy ,Solid-state ,02 engineering and technology ,engineering.material ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Martensite ,0103 physical sciences ,Thermal ,engineering ,Transformation hardening ,Grain boundary ,Tempering ,Electrical and Electronic Engineering ,0210 nano-technology - Abstract
For low-chromium ferritic stainless steel, a recently developed laser-driven drop-deposition technique enabled the building of three adjacent tracks on a substrate sheet of the same alloy, to study its risk for sensitisation from certain sequences of thermal cycles. The process was recorded by high-speed imaging to understand the drop-deposition mechanisms. Higher beam power resulted in a smoother track. The added layer was fully martensitic, achieving an elevated hardness of 320 HV. For a temperature peak just below austenitisation, the thermal cycle from a subsequent track affected the former track through tempering. Etching revealed a continuous region of ditched grain boundaries around the interface between the melted and heat affected zones. In the melted zone, the network became discontinuous approaching the surface, meaning that the specimen was immune to sensitisation, in contrast to transformation hardening results in the solid state. Additive manufacturing can induce manifold sequences of thermal cycles, but from the here generalized knowledge, strategies against sensitisation can be derived.
- Published
- 2018
10. Oxidation in wire arc additive manufacturing of aluminium alloys
- Author
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Tobias Hauser, Raven T. Reisch, Alexander Kaplan, Joerg Volpp, Kaivalya S. Joshi, Katharina Bela, Philipp Peter Breese, Yogesh Nalam, and Tobias Kamps
- Subjects
0209 industrial biotechnology ,Materials science ,Metallurgy ,Biomedical Engineering ,Oxide ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Industrial and Manufacturing Engineering ,Amorphous solid ,Volumetric flow rate ,ddc ,chemistry.chemical_compound ,020901 industrial engineering & automation ,chemistry ,Machining ,Aluminium ,visual_art ,Aluminium alloy ,visual_art.visual_art_medium ,General Materials Science ,Light emission ,0210 nano-technology ,Inert gas ,Engineering (miscellaneous) - Abstract
Wire Arc Additive Manufacturing is a near-net-shape machining technology that enables low-cost production of large and customised metal parts. In the present work, oxidation effects in Wire Arc Additive Manufacturing of the aluminium alloy AW4043/AlSi5(wt%) were investigated. Two main oxidation effects, the surface oxidation on aluminium parts and the oxidation anomalies in aluminium parts were observed and analysed. The surface oxidation on aluminium parts changed its colour during Wire Arc Additive Manufacturing from transparent to white. In the present work, it was shown by high-speed imaging that this change in the surface oxidation took place in the process zone, which was covered by inert gas. Since the white surface oxidation formed in an inert gas atmosphere, it was found that the arc interacts with the existing amorphous oxide layer of the previously deposited layer and turns it into a white duplex (crystalline and amorphous) oxide layer. In addition to the analysis of the white surface oxidation, oxidation anomalies, which occur at low shielding from the environment, were investigated. It was shown by physical experiments and Computational Fluid Dynamics simulations, that these oxidation anomalies occur at inadequate gas flow rates, too big nozzle-to-work distances, process modes with too high heat input, or too high wire feed rates. Finally, a monitoring method based on light emission spectroscopy was used to detect oxidation anomalies as they create peaks in the spectral emission when they occur.
- Published
- 2020
11. Porosity in wire arc additive manufacturing of aluminium alloys
- Author
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Benjamin Lutz, Joerg Volpp, Philipp Peter Breese, Tobias Hauser, Yogesh Nalam, Raven T. Reisch, Matteo Pantano, Tobias Kamps, Alexander Kaplan, and Katharina Bela
- Subjects
Convection ,0209 industrial biotechnology ,Work (thermodynamics) ,Materials science ,Shielding gas ,Biomedical Engineering ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Industrial and Manufacturing Engineering ,Forced convection ,Volumetric flow rate ,ddc ,Arc (geometry) ,020901 industrial engineering & automation ,chemistry ,Aluminium ,General Materials Science ,Composite material ,0210 nano-technology ,Porosity ,Engineering (miscellaneous) - Abstract
Wire Arc Additive Manufacturing is a near-net-shape processing technology which allows cost-effective manufacturing of large and customized metal parts. Processing of aluminium in Wire Arc Additive Manufacturing is quite challenging, especially in terms of porosity. In the present work, pore behaviour in Wire Arc Additive Manufacturing of AW4043/AlSi5(wt%) was investigated and a post-process monitoring approach was developed. It has been observed that as the shielding gas flow rate increases, the porosity in aluminium parts also increases due to the rapid solidification of the melt pool by forced convection. The higher convection rate seems to limit the escape of gas inclusions. Furthermore, gas inclusions escaping from the melt pool leave cavities on the surface of each deposited layer. Process camera imaging is used to monitor these cavities to acquire information about the porosity in the part. The observations were supported by Computational Fluid Dynamics simulations which show that the gas flow rate correlates with the porosity in aluminium parts manufactured by Wire Arc Additive Manufacturing. Since a lower gas flow rate leads to reduced convective cooling, the melt pool remains liquid for a longer period allowing pores to escape for a longer period and thus reducing porosity. Based on these investigations, a monitoring approach is presented.
- Published
- 2020
12. Fluctuation effects in Wire Arc Additive Manufacturing of aluminium analysed by high-speed imaging
- Author
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Adrien Da Silva, Joerg Volpp, Tobias Kamps, Raven T. Reisch, Tobias Hauser, and Alexander Kaplan
- Subjects
Work (thermodynamics) ,Materials science ,Manufacturing process ,Strategy and Management ,Process (computing) ,chemistry.chemical_element ,Ground and neutral ,Welding ,Management Science and Operations Research ,Industrial and Manufacturing Engineering ,law.invention ,ddc ,Arc (geometry) ,chemistry ,Aluminium ,law ,Composite material ,Lead (electronics) - Abstract
Wire Arc Additive Manufacturing is a near-net-shape processing technology which allows the cost-effective manufacturing of big and customized metal parts. In the present work the Wire Arc Additive Manufacturing of AW4043/AlSi5(wt.%) with different lead angles of the welding torch was investigated. It has been shown that for some lead angles fluctuation effects occur in the structures produced if the interlayer temperature is either too low or too high. All experiments were analysed by high-speed imaging whereby the welding phenomena could be observed. In the case of Wire Arc Additive Manufacturing with a lead angle above 10° at lower interlayer temperatures, the deposited track consists out of several, seperated WAAM globules and is no longer in a uniform track. In the case of the dragging and neutral Wire Arc Additive Manufacturing processes at higher interlayer temperatures, fluctuation effects occur. In addition, by evaluating the high-speed videos with computer vision, it was found that such fluctuation effects can be detected at the arc frequency of the process. To avoid fluctuation effects caused by too low or too high interlayer temperatures, a pushing Wire Arc Additive Manufacturing process with a slightly tilted lead angle should be used.
- Published
- 2019
13. The geometry of the cutting front created by Fibre and CO2 lasers when profiling stainless steel under standard commercial conditions
- Author
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Jan Frostevarg, Alexander Kaplan, Jetro Pocorni, and John Powell
- Subjects
010302 applied physics ,Profiling (computer programming) ,Co2 laser ,Brewster's angle ,Materials science ,Laser cutting ,Front (oceanography) ,Geometry ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Laser ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,symbols.namesake ,law ,Fiber laser ,0103 physical sciences ,Curve fitting ,symbols ,Electrical and Electronic Engineering ,0210 nano-technology - Abstract
Cutting fronts created by CO2 and fibre lasers in stainless steel at thicknesses between 2 mm and 10 mm have been ‘frozen’ and their geometry has been measured. Standard commercial cutting paramete ...
- Published
- 2018
14. Laser surface hardening of 11% Cr ferritic stainless steel and its sensitisation behaviour
- Author
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Timo Manninen, Alexander Kaplan, Hannu-Pekka Heikkinen, Jesper Sundqvist, and Severi Anttila
- Subjects
0209 industrial biotechnology ,Materials science ,Metallurgy ,02 engineering and technology ,Surfaces and Interfaces ,General Chemistry ,Lath ,engineering.material ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Microstructure ,Hardness ,Surfaces, Coatings and Films ,Corrosion ,Carbide ,020901 industrial engineering & automation ,Ferrite (iron) ,Martensite ,Materials Chemistry ,Hardening (metallurgy) ,engineering ,0210 nano-technology - Abstract
11% Cr ferritic stainless steel conforming to EN 1.4003 standard was surface hardened by a continuous-wave fibre laser beam. Both single-pass and multi-pass laser hardening was investigated. Different laser parameters were compared and their influence on hardness, microstructure, geometry of the hardened zone and sensitisation was investigated, especially for overlapping passes. The experiments showed that a surface hardness which is double that of the base material hardness was obtainable via martensitic phase transformation and high cooling rate, in spite of the low carbon and nitrogen content. This behaviour could be predicted from the chemical composition using the Kaltenhauser Ferrite Factor. Hardening at higher power levels gives more coarse-grained lath martensite but does not increase the hardness. Sensitisation was not a problem in single-pass hardening. However, the production of overlapping tracks could be detrimental to corrosion resistance in 11% Cr steel due to the formation of chromium carbides and nitrides.
- Published
- 2018
15. Holographic measurement of distortion during laser melting: Additive distortion from overlapping pulses
- Author
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Alexander Kaplan, Ingemar Eriksson, Jan Frostevarg, John Powell, and Peter Haglund
- Subjects
Thermal distortion ,Materials science ,business.industry ,technology, industry, and agriculture ,Holography ,02 engineering and technology ,Welding ,Bending ,021001 nanoscience & nanotechnology ,Laser ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,Pulse (physics) ,010309 optics ,Optics ,law ,Distortion ,0103 physical sciences ,Thermal ,Electrical and Electronic Engineering ,0210 nano-technology ,business - Abstract
Laser - material interactions such as welding, heat treatment and thermal bending generate thermal gradients which give rise to thermal stresses and strains which often result in a permanent distortion of the heated object. This paper investigates the thermal distortion response which results from pulsed laser surface melting of a stainless steel sheet. Pulsed holography has been used to accurately monitor, in real time, the out-of-plane distortion of stainless steel samples melted on one face by with both single and multiple laser pulses. It has been shown that surface melting by additional laser pulses increases the out of plane distortion of the sample without significantly increasing the melt depth. The distortion differences between the primary pulse and subsequent pulses has also been analysed for fully and partially overlapping laser pulses.
- Published
- 2018
16. Process stability during fiber laser-arc hybrid welding of thick steel plates
- Author
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Ivan Bunaziv, Odd M. Akselsen, Jan Frostevarg, and Alexander Kaplan
- Subjects
0209 industrial biotechnology ,Heat-affected zone ,Materials science ,Mechanical Engineering ,Gas tungsten arc welding ,Laser beam welding ,02 engineering and technology ,Welding ,Electrogas welding ,021001 nanoscience & nanotechnology ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,Gas metal arc welding ,020901 industrial engineering & automation ,law ,Welding power supply ,Arc welding ,Electrical and Electronic Engineering ,Composite material ,0210 nano-technology - Abstract
Thick steel plates are frequently used in shipbuilding, pipelines and other related heavy industries, and are usually joined by arc welding. Deep penetration laser-arc hybrid welding could increase productivity but has not been thoroughly investigated, and is therefore usually limited to applications with medium thickness (5-15 mm) sections. A major concern is process stability, especially when using modern welding consumables such as metal-cored wire and advanced welding equipment. High speed imaging allows direct observation of the process so that process behavior and phenomena can be studied. In this paper, 45 mm thick high strength steel was welded (butt joint double-sided) using the fiber laser-MAG hybrid process utilizing a metal-cored wire without pre-heating. Process stability was monitored under a wide range of welding parameters. It was found that the technique can be used successfully to weld thick sections with appropriate quality when the parameters are optimized. When comparing conventional pulsed and the more advanced cold metal transfer pulse (CMT+P) arc modes, it was found that both can provide high quality welds. CMT+P arc mode can provide more stable droplet transfer over a limited range of travel speeds. At higher travel speeds, an unstable metal transfer mechanism was observed. Comparing leading arc and trailing arc arrangements, the leading arc configuration can provide higher quality welds and more stable processing at longer inter-distances between the heat sources.
- Published
- 2018
17. Dynamic laser piercing of thick section metals
- Author
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John Powell, Jetro Pocorni, Jan Frostevarg, and Alexander Kaplan
- Subjects
Materials science ,Laser cutting ,business.industry ,Mechanical Engineering ,02 engineering and technology ,Thick section ,021001 nanoscience & nanotechnology ,Laser ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,010309 optics ,Optics ,law ,Fiber laser ,0103 physical sciences ,Electrical and Electronic Engineering ,0210 nano-technology ,business ,Productivity ,Reliability (statistics) - Abstract
Before a contour can be laser cut the laser first needs to pierce the material. The time taken to achieve piercing should be minimised to optimise productivity. One important aspect of laser pierci ...
- Published
- 2018
18. Behavior of heated powder particles on solid surfaces
- Author
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Alexander Kaplan, Joerg Volpp, and Himani Siva Prasad
- Subjects
Cladding (metalworking) ,0209 industrial biotechnology ,Materials science ,Solid surface ,Nozzle ,Laser additive manufacturing ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Industrial and Manufacturing Engineering ,020901 industrial engineering & automation ,Artificial Intelligence ,Composite material ,0210 nano-technology ,Laser beams - Abstract
Powder particles applied through a powder nozzle as used e.g. in laser additive manufacturing or cladding processes are heated during their flight through the laser beam. The heating process and th ...
- Published
- 2018
19. Powder particle attachment mechanisms onto liquid material
- Author
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Himani Siva Prasad, Mirko Riede, Frank Brueckner, Jörg Volpp, and Alexander Kaplan
- Subjects
Metal deposition ,0209 industrial biotechnology ,020901 industrial engineering & automation ,Materials science ,Chemical physics ,General Earth and Planetary Sciences ,Particle ,02 engineering and technology ,021001 nanoscience & nanotechnology ,0210 nano-technology ,General Environmental Science - Abstract
In order to achieve high powder and energy efficiencies of Direct Metal Deposition processes knowledge about the basic effects of the interaction of the particle on the liquid surface is mandatory. ...
- Published
- 2018
20. Numerical simulation of laser ablation driven melt waves
- Author
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Sang-Woo Han, Jetro Pocorni, Alexander Kaplan, Suck-Joo Na, Jason Cheon, and Hee-Seon Bang
- Subjects
010302 applied physics ,Laser ablation ,Materials science ,Computer simulation ,business.industry ,Strategy and Management ,Front (oceanography) ,02 engineering and technology ,Welding ,Management Science and Operations Research ,021001 nanoscience & nanotechnology ,Mathematics::Geometric Topology ,01 natural sciences ,Industrial and Manufacturing Engineering ,law.invention ,Mathematics::Algebraic Geometry ,Optics ,law ,Condensed Matter::Superconductivity ,Fiber laser ,0103 physical sciences ,0210 nano-technology ,business ,Keyhole ,Melt flow index - Abstract
Numerical simulations on the melt flow down the keyhole front during fibre laser welding are presented here. The calculations confirm the existence of melt waves previously observed by high speed i ...
- Published
- 2017
21. Spattering and oxidation phenomena during recycling of low alloy steel powder in Laser Powder Bed Fusion
- Author
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Alexander Kaplan, Tatiana Fedina, and Jesper Sundqvist
- Subjects
Fusion ,Materials science ,Economies of agglomeration ,Scanning electron microscope ,Metallurgy ,Alloy steel ,chemistry.chemical_element ,02 engineering and technology ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Oxygen ,0104 chemical sciences ,chemistry ,Mechanics of Materials ,Materials Chemistry ,engineering ,Degradation (geology) ,General Materials Science ,Particle size ,0210 nano-technology ,Ejecta - Abstract
This study reports on the impact of repeated powder recycling on the degradation of low alloy steel powder in Laser Powder Bed Fusion. The average powder particle size increased slightly upon recycling due to powder agglomeration and the presence of spatters and other ejecta from the process zone. The oxygen content showed a continuous growth after each recycle, while the other chemical elements of the recycled powder remained largely unchanged. A map of ejecta classification is presented, featuring various ejecta types formed during laser processing. Ejecta of increased diameter and different shapes were observed in the recycled powder, using high-speed imaging and Scanning Electron Microscopy. The ejecta were collected after each powder recycle to enable the calculation of the ejecta mass generated during the process. The result showed a direct correlation between oxygen content in the powder and spatter/ejecta formation with the number of recycling events. It is likely that the increase in oxygen contributes to powder spattering.
- Published
- 2021
22. The effects of laser irradiation on an aluminium powder stream in Directed Energy Deposition
- Author
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Alexander Kaplan, Joerg Volpp, and Adrien Da Silva
- Subjects
0209 industrial biotechnology ,Materials science ,Biomedical Engineering ,chemistry.chemical_element ,powder disintegration ,02 engineering and technology ,Industrial and Manufacturing Engineering ,law.invention ,Momentum ,020901 industrial engineering & automation ,power attenuation ,Aluminium ,law ,Deposition (phase transition) ,Manufacturing, Surface and Joining Technology ,General Materials Science ,Irradiation ,Laser power scaling ,Composite material ,Bearbetnings-, yt- och fogningsteknik ,Engineering (miscellaneous) ,recoil pressure ,021001 nanoscience & nanotechnology ,Laser ,chemistry ,Particle ,powder deviation ,Aluminium powder ,0210 nano-technology ,Direct Metal Deposition - Abstract
Additive Manufacturing with aluminium alloys is a subject of increasing industrial interest. Directed Energy Deposition using high power lasers and a powder feed is a useful option but the interactions between the powder stream and the laser beam are not completely understood. It is well known that the powder particles heat up in the laser beam and some theoretical models predict that they can reach their vaporisation temperature and have their flight path altered by the associated recoil pressure. In order to learn more about these phenomena, powder streams were observed with a high-speed camera at different laser powers (up to 6 kW) and with three batches of powder (AlSi10Mg) of different particle sizes. The results showed an increase of powder focussing with increased laser power. In addition, some particles were found to disintegrate in the laser beam. It is demonstrated that particle disintegration is most likely to be caused by the momentum induced by the recoil pressure. Validerad;2021;Nivå 2;2021-04-20 (alebob);Finansiär: EIT Raw Materials (18079)
- Published
- 2021
23. Evaluation of pre-determined dilution of high strength steels by the Snapshot method
- Author
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Jan Frostevarg, Alexander Kaplan, Jonas Näsström, Stephanie M. Robertson, and Therese Berndtsson
- Subjects
Cladding (metalworking) ,Toughness ,Materials science ,Mechanical Engineering ,Metallurgy ,Laser beam welding ,Welding ,Microstructure ,Atomic and Molecular Physics, and Optics ,Acicular ferrite ,Electronic, Optical and Magnetic Materials ,law.invention ,Dilution ,Machining ,law ,Electrical and Electronic Engineering - Abstract
Dilution is an unavoidable consequence of multi-material fusion processing, i.e. welding, cladding etc. In this paper we propose a novel method for controlled dilution experiments, analyzing microstructural trends of steel filler wire diluted with steel base metal. The highlight of this method is the control of processing conditions used to melt a pre-determined dilution of two high strength steels. The materials involved are S960QL base metal machining chips and a chopped under-matched wire consumable, which is used to increase the toughness of welded joints. These materials were combined in specific mass ratios in a prepared cavity and then melted by a pulsed laser beam. A high-speed RGB camera evaluated the relative spatial temperature of the melt surface. The molten mass then solidified into a uniform nugget, confirmed by energy dispersive x-ray spectrometry (EDS) to have a homogenous chemical composition (a ‘Snapshot’ nugget). Hardness values obtained for different dilution levels were compared to a narrow gap multi-layer laser weld (NGMLW), with a decreased dilution rate yielding a decreased hardness. The Snapshot microstructures created are similar to the different regions of the NGMLW, in the weld cap and in the body of the weld. Snapshot nuggets were also evaluated for non-metallic inclusion (NMI) size distributions relating to the dilution levels (NMIs are important indicators for acicular ferrite, which has been shown to increase impact toughness).
- Published
- 2021
24. Analytical heat conduction modelling for shaped laser beams
- Author
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Jesper Sundqvist, Alexander Kaplan, Choon Yen Kong, and L. Shachaf
- Subjects
0209 industrial biotechnology ,Materials science ,02 engineering and technology ,Welding ,Beam parameter product ,Industrial and Manufacturing Engineering ,law.invention ,020901 industrial engineering & automation ,Optics ,law ,Spot welding ,Computer Science::Databases ,business.industry ,Metals and Alloys ,Laser beam welding ,021001 nanoscience & nanotechnology ,Thermal conduction ,Laser ,Computer Science Applications ,Modeling and Simulation ,Ceramics and Composites ,Physics::Accelerator Physics ,M squared ,Laser beam quality ,0210 nano-technology ,business - Abstract
Conduction mode laser spot welding and laser spot hardening usually employ Gaussian or top-hat-like beam modes. One main requirement of these techniques is the avoidance of overheating in the centre of the laser-material interaction zone. Process flexibility can be improved by spatially and/or temporally shaping the beam, which can enable higher process quality, robustness or speed. A desired spatial beam shape can be achieved by a suitably designed diffractive optical element. However, the prediction of a suitable beam shape for a particular process can be complex. A simplified analytical heat conduction model has been developed that can rapidly calculate the temperature field and cooling behaviour for almost any spatial and temporal beam shape. The potential and limits of the model are demonstrated and discussed by calculating and analysing temperature profiles for several cases of multi-spot welding.
- Published
- 2017
25. Using laser cutting as a source of molten droplets for additive manufacturing: A new recycling technique
- Author
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Alexander Kaplan and Ramiz Saeed Matti Samarjy
- Subjects
Engineering drawing ,Materials science ,Laser cutting ,chemistry.chemical_element ,02 engineering and technology ,Substrate (printing) ,01 natural sciences ,law.invention ,law ,Aluminium ,0103 physical sciences ,lcsh:TA401-492 ,Deposition (phase transition) ,General Materials Science ,Composite material ,010302 applied physics ,Jet (fluid) ,Fusion ,Mechanical Engineering ,021001 nanoscience & nanotechnology ,Laser ,chemistry ,Mechanics of Materials ,lcsh:Materials of engineering and construction. Mechanics of materials ,Wetting ,0210 nano-technology - Abstract
A new variant of additive manufacturing is proposed which involves transferring molten droplets via a laser beam to a substrate. The droplets are generated by laser remote fusion cutting of a supply sheet that could be a waste material, for recycling purposes. The laser-induced ablation pressure at the cutting front continuously drives melt downwards below the supply sheet in the form of a liquid column. Droplets separate from the column and solidify as a track on a substrate below. The droplets, surrounded by vapour, had in this case an average diameter of 500 μm and a speed of 2 m/s, with deviations up to 50%. Sound clad tracks were generated on steel and aluminium substrates. In the case of a copper substrate discontinuous clad tracks were produced as a result of poor wetting. The droplet jet had a small divergence of about 5°, which is suitable for controlled deposition. The transmitted part of the laser beam interacted with the clad track but did not affect the process result. High speed imaging was found to be a suitable tool for qualitative and quantitative analysis of the technique. Keywords: Additive manufacturing, Laser remote fusion cutting, Ablation, High speed imaging, Deposition, Droplet
- Published
- 2017
26. Assessing motor imagery in brain-computer interface training: Psychological and neurophysiological correlates
- Author
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Anatoly N. Vasilyev, Lev Yakovlev, Liburkina Sp, Olga Perepelkina, and Alexander Kaplan
- Subjects
Adult ,Male ,medicine.medical_specialty ,Cognitive Neuroscience ,medicine.medical_treatment ,Experimental and Cognitive Psychology ,Motor Activity ,Electroencephalography ,050105 experimental psychology ,Young Adult ,03 medical and health sciences ,Behavioral Neuroscience ,0302 clinical medicine ,Motor imagery ,Physical medicine and rehabilitation ,medicine ,Humans ,0501 psychology and cognitive sciences ,Motor skill ,Neurorehabilitation ,Brain–computer interface ,Cerebral Cortex ,medicine.diagnostic_test ,05 social sciences ,Brain Waves ,Transcranial Magnetic Stimulation ,Transcranial magnetic stimulation ,Disinhibition ,Brain-Computer Interfaces ,Imagination ,Auditory imagery ,Female ,medicine.symptom ,Psychology ,Neuroscience ,030217 neurology & neurosurgery - Abstract
Motor imagery (MI) is considered to be a promising cognitive tool for improving motor skills as well as for rehabilitation therapy of movement disorders. It is believed that MI training efficiency could be improved by using the brain-computer interface (BCI) technology providing real-time feedback on person's mental attempts. While BCI is indeed a convenient and motivating tool for practicing MI, it is not clear whether it could be used for predicting or measuring potential positive impact of the training. In this study, we are trying to establish whether the proficiency in BCI control is associated with any of the neurophysiological or psychological correlates of motor imagery, as well as to determine possible interrelations among them. For that purpose, we studied motor imagery in a group of 19 healthy BCI-trained volunteers and performed a correlation analysis across various quantitative assessment metrics. We examined subjects' sensorimotor event-related EEG events, corticospinal excitability changes estimated with single-pulse transcranial magnetic stimulation (TMS), BCI accuracy and self-assessment reports obtained with specially designed questionnaires and interview routine. Our results showed, expectedly, that BCI performance is dependent on the subject's capability to suppress EEG sensorimotor rhythms, which in turn is correlated with the idle state amplitude of those oscillations. Neither BCI accuracy nor the EEG features associated with MI were found to correlate with the level of corticospinal excitability increase during motor imagery, and with assessed imagery vividness. Finally, a significant correlation was found between the level of corticospinal excitability increase and kinesthetic vividness of imagery (KVIQ-20 questionnaire). Our results suggest that two distinct neurophysiological mechanisms might mediate possible effects of motor imagery: the non-specific cortical sensorimotor disinhibition and the focal corticospinal excitability increase. Acquired data suggests that BCI-based approach is unreliable in assessing motor imagery due to its high dependence on subject's innate EEG features (e.g. resting mu-rhythm amplitude). Therefore, employment of additional assessment protocols, such as TMS and psychological testing, is required for more comprehensive evaluation of the subject's motor imagery training efficiency.
- Published
- 2017
27. CYCLAM - Recycling by a Laser-driven Drop Jet from Waste that Feeds AM
- Author
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Alexander Kaplan and Ramiz Saeed Matti Samarjy
- Subjects
010302 applied physics ,Materials science ,business.industry ,Drop (liquid) ,Metallurgy ,3D printing ,02 engineering and technology ,Raw material ,021001 nanoscience & nanotechnology ,Laser ,01 natural sciences ,law.invention ,chemistry.chemical_compound ,chemistry ,law ,0103 physical sciences ,Cyclam ,Hardware_INTEGRATEDCIRCUITS ,0210 nano-technology ,business - Abstract
Additive manufacturing of metal parts is supplied by powder or wire. Manufacturing of this raw material causes additional costs and environmental impact. A new technique is proposed where the feedi ...
- Published
- 2017
28. Transient interaction of a boiling melt with a pulsed Nd:YAG-laser
- Author
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Alexander Kaplan and Ramiz Saeed Matti Samarjy
- Subjects
010302 applied physics ,Materials science ,Mechanical Engineering ,Front (oceanography) ,Drilling ,02 engineering and technology ,Welding ,Mechanics ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,Surface tension ,Cross section (physics) ,law ,Boiling ,Nd:YAG laser ,0103 physical sciences ,Electrical and Electronic Engineering ,0210 nano-technology ,Keyhole - Abstract
The boiling front induced by a pulsed Nd:YAG-laser at very slow translation speed was studied. The purpose is to understand fundamental melt movement mechanisms. The melt was observed by high speed imaging, with and without illumination. When switching on the laser beam a hole is drilled through a bulk of melt. The hole expands and the boiling pressure gradually opens the melt bridge, instead developing an interaction front similar to cutting. These conditions remain in quasi-steady state during the pulse. The ablation pressure from boiling shears waves down the front and keeps the melt downwards in a stable position. When switching off, the waves smoothen and in absence of boiling the surface tension drags the melt back upwards, to semi-torus-like Catenoid shape. Evidence on the large melt pool and its shape was achieved by three-dimensional reconstruction from cross section macrographs. The basic findings how melt can move with and without ablation pressure can enable controlled melt dynamics for various laser processing techniques, like remote cutting, ablation, keyhole welding or drilling.
- Published
- 2017
29. Fibre laser cutting stainless steel: Fluid dynamics and cut front morphology
- Author
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Jetro Pocorni, Jan Frostevarg, Alexander Kaplan, Eckard Deichsel, and John Powell
- Subjects
0209 industrial biotechnology ,Morphology (linguistics) ,Materials science ,business.industry ,Laser cutting ,digestive, oral, and skin physiology ,Front (oceanography) ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Laser ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,020901 industrial engineering & automation ,Optics ,Particle tracking velocimetry ,law ,Fiber laser ,Fluid dynamics ,Physics::Atomic Physics ,Electrical and Electronic Engineering ,0210 nano-technology ,business ,Nonlinear Sciences::Pattern Formation and Solitons ,Melt flow index - Abstract
In this paper the morphology of the laser cut front generated by fibre lasers was investigated by observation of the ‘frozen’ cut front, additionally high speed imaging (HSI) was employed to study ...
- Published
- 2017
30. A comparative study of water and gas atomized low alloy steel powders for additive manufacturing
- Author
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Alexander Kaplan, Tatiana Fedina, Jesper Sundqvist, and John Powell
- Subjects
0209 industrial biotechnology ,Materials science ,Alloy steel ,Metallurgy ,Biomedical Engineering ,Particle entrainment ,chemistry.chemical_element ,02 engineering and technology ,engineering.material ,021001 nanoscience & nanotechnology ,Oxygen ,Industrial and Manufacturing Engineering ,020901 industrial engineering & automation ,chemistry ,engineering ,Particle ,Track formation ,General Materials Science ,Irradiation ,0210 nano-technology ,Melt pool ,Engineering (miscellaneous) ,Laser processing - Abstract
This work reports a study of the differences between laser processing of water and gas atomized low alloy steel powders with a focus on powder behavior and performance in additive manufacturing. Material packing densities were measured to establish a relationship between powder packing and track formation. The results showed that the track height when using water atomized powder was 15% lower than the value achieved for the gas atomized powder. High-speed imaging was utilized to observe the material behavior and analyze the powder particle movement under laser irradiation. It was found that water atomized powder has less particle entrainment due to its tendency towards mechanical interlocking. The occurrence of powder spattering and melt pool instabilities was also studied. More frequent spatter ejection is believed to be due to the higher amount of oxygen in the water atomized powder.
- Published
- 2020
31. Closed-form orthotropic constitutive model for aligned square array mesostructure
- Author
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Ruiqi Chen, Alexander Kaplan, and Debbie G. Senesky
- Subjects
0209 industrial biotechnology ,Materials science ,Mathematical analysis ,Constitutive equation ,Biomedical Engineering ,Hypotrochoid ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Orthotropic material ,Antiplane shear ,Industrial and Manufacturing Engineering ,Shape parameter ,Finite element method ,020901 industrial engineering & automation ,General Materials Science ,Elasticity (economics) ,0210 nano-technology ,Porosity ,Engineering (miscellaneous) - Abstract
This work models the square array mesostructure found in fused filament fabrication parts using an orthotropic constitutive model and derives closed-form expressions for all nine effective elastic constants. The periodic void shape is modeled using a four point hypotrochoid curve with a single shape parameter that controls the sharpness of the points. In-plane elastic constants ( E y y , E z z , v y z , G y z ) are derived by solving the 2D elasticity equations using the complex variable method of elasticity. The antiplane shear constants ( G x y and G x z ) are derived from a complex variable formulation of the antiplane shear equations. The remaining elastic constants ( E x x , v x y , and v x z ) are derived by directly solving the linearelasticity equations. We compare our results to unit cell finite element simulations. The simulations match the closed-form expressions exactly for E x x , v x y , and v x z . For the remaining elastic constants, the difference between closed-form model and simulation increases as porosity increases. Tensile testing specimens at various porosity values under 12% are fabricated to test six of the nine elastic constants. Experiments on E x x , v x y , and v x z agree well with closed-form predictions, differing by less than 2.6% for the tested specimen types. Experiments on E y y , E z z , and G x y generally agree well, with larger differences at higher porosity values. The difference is less than 6% for all tested specimen types except for the E zz specimen with a porosity of 0.113, which had a difference of 21%. Several reasons for the discrepancy are postulated, including non-ideal void shape and interfacial bond stiffness.
- Published
- 2020
32. Powder incorporation and spatter formation in high deposition rate blown powder directed energy deposition
- Author
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Alexander Kaplan, Himani Siva Prasad, and Frank Brueckner
- Subjects
0209 industrial biotechnology ,Materials science ,Molten metal ,Flow (psychology) ,Biomedical Engineering ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Rotation ,Laser ,Industrial and Manufacturing Engineering ,law.invention ,Deposition rate ,Surface tension ,020901 industrial engineering & automation ,law ,Deposition (phase transition) ,General Materials Science ,Composite material ,0210 nano-technology ,Engineering (miscellaneous) ,Laser beams - Abstract
A high deposition rate blown powder directed energy deposition process is presented. Clad tracks are deposited and the process is observed by high-speed imaging. An island of unmelted powder forms inside the melt pool, in the centre of the laser spot, which can be attributed to the highly focussed powder flow and the laser beam configuration used. On contact with the melt pool, the powder grains melt to join the melt pool, or they overcome surface tension and are engulfed by the melt. Powder grains can also incorporate into a mushy zone that may be present on the powder island. The powder island appears to rotate in the melt pool and incorporates relatively slowly. The speed of rotation is connected to the size of the island, which also depends on the energy density used. Spatter can form from the edges of the melt pool or from areas around the island when molten metal droplets burst. Frames from high-speed videos are presented and reasons for the various phenomena observed are discussed.
- Published
- 2020
33. Modulation of critical brain dynamics using closed-loop neurofeedback stimulation
- Author
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Alexander Zhigalov, Alexander Kaplan, and J. Matias Palva
- Subjects
Male ,0301 basic medicine ,Neuroregulation ,Stimulation ,Sensory system ,Stimulus (physiology) ,Electroencephalography ,Young Adult ,03 medical and health sciences ,0302 clinical medicine ,Physiology (medical) ,medicine ,Humans ,Brain Mapping ,medicine.diagnostic_test ,Brain ,Signal Processing, Computer-Assisted ,Cognition ,Neurofeedback ,Brain Waves ,Sensory Systems ,030104 developmental biology ,medicine.anatomical_structure ,Neurology ,Scalp ,Female ,Neurology (clinical) ,Psychology ,Neuroscience ,Photic Stimulation ,030217 neurology & neurosurgery - Abstract
Objective EEG long-range temporal correlations (LRTCs) are a significant for both human cognition and brain disorders, but beyond suppression by sensory disruption, there are little means for influencing them non-invasively. We hypothesized that LRTCs could be controlled by engaging intrinsic neuroregulation through closed-loop neurofeedback stimulation. Methods We used a closed-loop-stimulation paradigm where supra-threshold α-waves trigger visual flash stimuli while the subject performs the standard eyes-closed resting-state task. As a "sham" control condition, we applied similar stimulus sequences without the neurofeedback. Results Over three sessions, a significant difference in the LRTCs of α-band oscillations ( U =89, p Wilcoxon rank sum test ) and their scalp topography ( T =−2.92, p T-test ) emerged between the neurofeedback and sham conditions so that the LRTCs were stronger during neurofeedback than sham. No changes ( F =0.16, p >0.69, ANOVA test ) in the scalp topography of α - band power were observed in either condition. Conclusions This study provides proof-of-concept for that EEG LRTCs, and hence critical brain dynamics, can be modulated with closed-loop stimulation in an automatic, involuntary fashion. We suggest that this modulation is mediated by an excitation–inhibition balance change achieved by the closed-loop neuroregulation. Significance Automatic LRTC modulation opens novel avenues for both examining the functional roles of brain criticality in healthy subjects and for developing novel therapeutic approaches for brain disorders associated with abnormal LRTCs.
- Published
- 2016
34. Numerical optimization approaches of single-pulse conduction laser welding by beam shape tailoring
- Author
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Eurico Assunção, Alexander Brodsky, Jesper Sundqvist, L. Shachaf, Alexander Kaplan, Luísa Quintino, C. Kong, and Jon Blackburn
- Subjects
010302 applied physics ,Materials science ,business.industry ,Mechanical Engineering ,Process (computing) ,Laser beam welding ,02 engineering and technology ,Welding ,021001 nanoscience & nanotechnology ,Thermal conduction ,01 natural sciences ,Beam parameter product ,Atomic and Molecular Physics, and Optics ,Control volume ,Electronic, Optical and Magnetic Materials ,law.invention ,Optics ,law ,0103 physical sciences ,Heat transfer ,Physics::Accelerator Physics ,Laser beam quality ,Electrical and Electronic Engineering ,0210 nano-technology ,business - Abstract
While circular laser beams are usually applied in laser welding, for certain applications tailoring of the laser beam shape, e.g. by diffractive optical elements, can optimize the process. A case where overlap conduction mode welding should be used to produce a C-shaped joint was studied. For the dimensions studied in this paper, the weld joint deviated significantly from the C-shape of the single-pulse laser beam. Because of the complex heat flow interactions, the process requires optimization. Three approaches for extracting quantitative indicators for understanding the essential heat flow contributions process and for optimizing the C-shape of the weld and of the laser beam were studied and compared. While integral energy properties through a control volume and temperature gradients at key locations only partially describe the heat flow behaviour, the geometrical properties of the melt pool isotherm proved to be the most reliable method for optimization. While pronouncing the C-ends was not sufficient, an additional enlargement of the laser beam produced the desired C-shaped weld joint. The approach is analysed and the potential for generalization is discussed.
- Published
- 2016
35. Combination of laser keyhole and conduction welding: Dissimilar laser welding of niobium and Ti-6Al-4V
- Author
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Mohammad Javad Torkamany, F. Malek Ghaini, Reza Poursalehi, and Alexander Kaplan
- Subjects
0209 industrial biotechnology ,Heat-affected zone ,Materials science ,Mechanical Engineering ,Niobium ,Titanium alloy ,chemistry.chemical_element ,Laser beam welding ,02 engineering and technology ,Welding ,021001 nanoscience & nanotechnology ,Laser ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,020901 industrial engineering & automation ,chemistry ,law ,Butt joint ,Electrical and Electronic Engineering ,Composite material ,0210 nano-technology ,Keyhole - Abstract
Pulsed Nd:YAG laser welding of pure niobium plate to titanium alloy Ti-6Al-4V sheet in butt joint is studied regarding the laser/metal interaction modes. To obtain the optimized process parameters in dissimilar welding of Ti-6Al-4V/Nb, the melting ratio of laser beam energy for each weld counterpart is evaluated experimentally. Different laser welding modes of keyhole and conduction are predicted regarding the absorbed energy from the similar laser pulses on each weld counterpart. Laser keyhole and conduction welding were observed simultaneously through direct visualization of laser interaction with dissimilar metals using High Speed Imaging (HSI) system.
- Published
- 2016
36. Imaging of the Dynamic Melt Movement Induced by a Pulsed Laser
- Author
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Alexander Kaplan and Ramiz Saeed Matti Samarjy
- Subjects
010302 applied physics ,Materials science ,Laser beam welding ,02 engineering and technology ,Mechanics ,Physics and Astronomy(all) ,021001 nanoscience & nanotechnology ,Laser ,01 natural sciences ,law.invention ,Surface tension ,Superheating ,boiling ,law ,Boiling ,pulsed laser ,0103 physical sciences ,melt flow ,remote cutting ,0210 nano-technology ,high speed imaging ,Keyhole ,Laser drilling ,Melt flow index - Abstract
A special case of an interrupted superheated process was developed, governed by the ablation pressure of a boiling melt, induced by a pulsed Nd:YAG-laser. A kind of cutting process was carried out, but at very low speed to generate a large melt pool that can be well studied. The interaction zone was observed by high speed imaging, with and without illumination. When switching the laser pulse on or off, different dynamic phenomena can be clearly observed, like drilling into a bulk of melt, breaking of a melt bridge, controlled pushing of the melt pool, waves running down, all driven by boiling. After the pulse, the melt smoothens and oscillates and is dragged back upwards by the surface tension forces from the melt shape curvature, ending in a torus-like equilibrium shape. The fundamental understanding that was generated could be applied to improve processes like keyhole laser welding, laser remote fusion cutting or laser drilling
- Published
- 2016
- Full Text
- View/download PDF
37. Post-modelling of images from a laser-induced wavy boiling front
- Author
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Ramiz Matti and Alexander Kaplan
- Subjects
Materials science ,business.industry ,Laser cutting ,Front (oceanography) ,Physics::Optics ,General Physics and Astronomy ,Surfaces and Interfaces ,General Chemistry ,Welding ,Condensed Matter Physics ,Laser ,Surfaces, Coatings and Films ,law.invention ,Wavelength ,Optics ,law ,Boiling ,business ,Keyhole ,Laser drilling - Abstract
Processes like laser keyhole welding, remote fusion laser cutting or laser drilling are governed by a highly dynamic wavy boiling front that was recently recorded by ultra-high speed imaging. A new approach has now been established by post-modelling of the high speed images. Based on the image greyscale and on a cavity model the three-dimensional front topology is reconstructed. As a second step the Fresnel absorptivity modulation across the wavy front is calculated, combined with the local projection of the laser beam. Frequency polygons enable additional analysis of the statistical variations of the properties across the front. Trends like shadow formation and time dependency can be studied, locally and for the whole front. Despite strong topology modulation in space and time, for lasers with 1 μm wavelength and steel the absorptivity is bounded to a narrow range of 35–43%, owing to its Fresnel characteristics.
- Published
- 2015
38. Gap bridging for two modes of laser arc hybrid welding
- Author
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Javier Lamas, Jan Frostevarg, and Alexander Kaplan
- Subjects
Heat-affected zone ,Materials science ,Bridging (networking) ,Metals and Alloys ,Welding ,Laser ,Engineering physics ,Industrial and Manufacturing Engineering ,Computer Science Applications ,law.invention ,law ,Modeling and Simulation ,Ceramics and Composites ,Gap width ,Composite material - Abstract
The topology of welds is an important quality criterion for which the mechanisms behind are only partially understood. The impact of gap width on the resulting weld shape produced by laser-arc hybr ...
- Published
- 2015
39. Material transitions within multi-material laser deposited intermetallic iron aluminides
- Author
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Tobias Kamps, Joerg Volpp, Philipp Peter Breese, Christoph Heinze, Tobias Hauser, and Alexander Kaplan
- Subjects
0209 industrial biotechnology ,Work (thermodynamics) ,Materials science ,Biomedical Engineering ,Multi material ,Intermetallic ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Laser ,Industrial and Manufacturing Engineering ,law.invention ,020901 industrial engineering & automation ,law ,Vertical direction ,General Materials Science ,Composite material ,Diffusion (business) ,0210 nano-technology ,Engineering (miscellaneous) ,Mixing (physics) ,Melt flow index - Abstract
Laser Metal Deposition is a near-net-shape processing technology, which allows remarkable freedom in multi-material processing. In the present work, the multi-material processing of two intermetallic iron aluminides, Fe28Al(at.%) and Fe30Al5Ti0.7B(at.%), was investigated. It has been shown that multi-material processing of the two alloys via discrete as well as via gradual material transition is possible without any cracks for manufacturing small cubes. Cross-sections of manufactured parts and tracks showed that a preheating temperature of at least 400 °C is necessary to process crack free samples. EDX-analyses indicated that if a discrete material transition is required in multi-material processing, the material transition should be implemented in the vertical build-up direction because the mixing zone in this direction is significantly smaller than the mixing zone in the horizontal direction. Due to the stronger mixing effects in the horizontal direction, a gradual material transition by a linear progression should be implemented in this direction rather than in the vertical direction. The mixing effects are mainly caused by melt flow, while diffusion effects can be neglected.
- Published
- 2020
40. Imperfections in narrow gap multi-layer welding - Potential causes and countermeasures
- Author
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Alexander Kaplan, Jonas Näsström, and Frank Brueckner
- Subjects
Data collection ,Computer science ,Mechanical Engineering ,Pipeline (computing) ,Process (computing) ,Mechanical engineering ,Laser beam welding ,02 engineering and technology ,Welding ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,010309 optics ,law ,0103 physical sciences ,Narrow gap ,Process control ,Electrical and Electronic Engineering ,0210 nano-technology ,Joint (geology) - Abstract
Narrow Gap Multi-Layer Welding (NGMLW) using a laser as the main heat source and metal wire for material addition has been a growing topic of interest in the last decade. This is in part due to its potential for joining much thicker sheets of steel than what is usually considered possible when using autogenous laser welding. The process has shown great potential but improvements can still be made, e.g. through increased process control to decrease welding imperfections. Using closed-loop control, where the process is continuously monitored and regulated automatically, can help to account for variations during manufacturing. However, achieving functional closed loop control can be challenging due to limitations in data gathering and processing speeds. Important initial steps include identifying what data can be useful and how frequently this data has to be recorded. Too much data takes too long to process while too little causes risks of missing important details. In this study, 20 mm thick X80 pipeline steel sheets are joined together using this multi-layer approach; the samples are examined using 3D scanning and Computed Tomography (CT) analysis and the process is observed using High-Speed Imaging (HSI). The quality of the welded joint and welding imperfections are discussed and potential points of formation are identified. Suggestions on how to mitigate imperfections to improve the quality of the welded joint are presented, including the potential to use camera imaging for closed-loop process control and additional industrial uses of the HSI footage.
- Published
- 2020
41. A near-vertical approach to Laser Narrow Gap Multi-Layer Welding
- Author
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Jonas Näsström, Frank Brueckner, and Alexander Kaplan
- Subjects
0209 industrial biotechnology ,Materials science ,Orientation (computer vision) ,business.industry ,Process (computing) ,Laser beam welding ,02 engineering and technology ,Surface finish ,Welding ,021001 nanoscience & nanotechnology ,Track (rail transport) ,Laser ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,020901 industrial engineering & automation ,Optics ,law ,Perpendicular ,Electrical and Electronic Engineering ,0210 nano-technology ,business - Abstract
A novel, near-vertical approach to the usually horizontal laser Narrow Gap Multi-Layer Welding process is introduced. The process is applied to join X100 pipeline steel and studied through High Speed Imaging. The produced welded joints are compared to their horizontally welded counterparts using 3D scanning, longitudinal & perpendicular cross sections and Computed Tomography analysis. The near-vertical approach is found to be robust and produce welded joints with a uniform appearance. The top surface exhibits certain reoccurring morphological features, and variations in internal track melting boundaries are observed. Any observed cavities appear similar to those produced using the horizontal process, with the difference of their orientation. A combination of the horizontal and the near-vertical process could be beneficial; the near-vertical approach offers potential for shorter inter-layer time and the horizontal method for better surface finish than that of its counterpart. Potential benefits of, and improvements to, the near-vertical process are discussed.
- Published
- 2020
42. Wire deposition by a laser-induced boiling front
- Author
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M. J. Torkamany, Alexander Kaplan, Mikko Vänskä, Joakim Hedegård, F. Malek Ghaini, Antti Salminen, and Karl Fahlström
- Subjects
Materials science ,medicine.medical_treatment ,Front (oceanography) ,Laser beam welding ,Welding ,Ablation ,Laser ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,law ,Boiling ,medicine ,Deposition (phase transition) ,Electrical and Electronic Engineering ,Composite material ,Keyhole - Abstract
In laser materials processing the addition of material by wire is an option for techniques like laser welding, laser cladding or rapid prototyping. The stability of the wire deposition is strongly dependent on the wire interaction with the laser beam. For leading position wire feeding, high speed imaging was applied to study the melt transfer from the wire tip to the workpiece during keyhole welding. The observations revealed that a very stable concave processing front forms at the wire tip. A boiling front is established as an extension of the keyhole and the melt film at the front is sheared downwards by the ablation pressure of boiling. The deposition of the molten wire into the weld zone is smooth and controllable. Various wire front geometries and melt transitions are compared for different parameters. The option of laterally oscillating the laser beam is investigated and the interaction mechanism involved is discussed. Wire deposition by inducing a boiling front is explained here for the first time, which should promote future applications use of this very promising technique.
- Published
- 2015
43. Laser welding of duplex stainless steel with nitrogen as shielding gas
- Author
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Kari Mäntyjärvi, Markku Keskitalo, John Powell, Jesper Sundqvist, and Alexander Kaplan
- Subjects
Heat-affected zone ,Materials science ,Gas tungsten arc welding ,fungi ,Shielding gas ,Metallurgy ,technology, industry, and agriculture ,Metals and Alloys ,food and beverages ,Shielded metal arc welding ,Laser beam welding ,Welding ,respiratory system ,Industrial and Manufacturing Engineering ,Computer Science Applications ,law.invention ,Gas metal arc welding ,law ,Modeling and Simulation ,Ceramics and Composites ,Arc welding ,Composite material - Abstract
Nitrogen loss from laser welding melts pools and can have a deleterious effect on weld toughness for duplex stainless steels. This effect can be alleviated by using nitrogen as the shielding gas during laser welding. The use of nitrogen results in increased austenite levels in the weld metal and improved toughness levels.
- Published
- 2015
44. Laser Welding Process – A Review of Keyhole Welding Modelling
- Author
-
Josefine Svenungsson, Alexander Kaplan, and Isabelle Choquet
- Subjects
melting ,Materials science ,Applied Mechanics ,Teknisk mekanik ,Conduction mode ,Process (computing) ,Mechanical engineering ,Laser beam welding ,modeling ,Welding ,Plasma ,Physics and Astronomy(all) ,Cw laser ,Fresnel absorptions ,law.invention ,law ,keyhole ,inverse Bremsstralhung absorption ,vapor flow ,Pulsed wave ,liquid flow ,Keyhole ,plasma ,vaporization - Abstract
Laser welding is used in several industrial applications. It can be distinguished between conduction mode and keyhole mode welding, between pulsed wave and cw laser welding and between CO2-lasers with a wavelength of 10μm and various laser types of about 1μm wavelength. A deeper understanding of laser welding allows improving weld quality, process control and process efficiency. It requires a complementary combination of precise modelling and experimental investigations. The here presented review focuses on modelling of laser keyhole welding, for both wavelength regimes. First, the fundamentals of the laser welding process and its physics such as beam propagation, keyhole formation and melt pool dynamics are addressed. The main approaches for modeling energy transfer from laser beam to keyhole surface as well as fluid flow in the material are then discussed. The most relevant publications are systematically structured, particularly categorized with regard to the respective physical phenomena addressed. Finally some open questions are underlined.
- Published
- 2015
45. Analyzing and Post-modelling the High Speed Images of a Wavy Laser Induced Boiling Front
- Author
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Ramiz Matti and Alexander Kaplan
- Subjects
Materials science ,topology ,Flow (psychology) ,02 engineering and technology ,boiling front ,Physics and Astronomy(all) ,01 natural sciences ,law.invention ,modelling ,Optics ,law ,Boiling ,0103 physical sciences ,Fluid dynamics ,Absorption (electromagnetic radiation) ,high speed imaging ,010302 applied physics ,business.industry ,Front (oceanography) ,021001 nanoscience & nanotechnology ,Flashing ,Laser ,absorptivity ,0210 nano-technology ,business ,Keyhole - Abstract
The boiling front in laser materials processing like remote fusion cutting, keyhole welding or drilling can nowadays be recorded by high speed imaging. It was recently observed that bright waves flow down the front. Several complex physical mechanisms are associated with a stable laser-induced boiling front, like beam absorption, shadowing, heating, ablation pressure, fluid flow, etc. The evidence of dynamic phenomena from high speed imaging is closely linked to these phenomena. As a first step, the directly visible phenomena were classified and analyzed. This has led to the insight that the appearance of steady flow of the bright front peaks is a composition of many short flashing events of 20-50 μs duration, though composing a rather constant melt film flow downwards. Five geometrical front shapes of bright and dark domains were categorized, for example long inclined dark valleys. In addition, the special top and bottom regions of the front are distinguished. As a second step, a new method of post-modelling based on the greyscale variation of the images was applied, to approximately reconstruct the topology of the wavy front and subsequently to calculate the absorption across the front. Despite certain simplifications this kind of analysis provides a variety of additional information, including statistical analysis. In particular, the model could show the sensitivity of front waves to the formation of shadow domains and the robustness of fiber lasers to keep most of an irradiated steel surface in an absorptivity window between 35 to 43%.
- Published
- 2015
- Full Text
- View/download PDF
46. Measuring the Melt Flow on the Laser Cut Front
- Author
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Dirk Petring, Eckard Deichsel, Alexander Kaplan, John Powell, Jetro Pocorni, and Publica
- Subjects
0209 industrial biotechnology ,Materials science ,Laser cutting ,Flow (psychology) ,02 engineering and technology ,Physics and Astronomy(all) ,law.invention ,fiber laser ,020901 industrial engineering & automation ,Optics ,Particle tracking velocimetry ,law ,Fiber laser ,High-speed photography ,ddc:530 ,Melt flow index ,high speed photography ,business.industry ,Front (oceanography) ,021001 nanoscience & nanotechnology ,Laser ,particle tracking velocimetry ,melt flow ,0210 nano-technology ,business - Abstract
15th Nordic Laser Materials Processing Conference, Nolamp 15 / Edited by Antti Salminen 15th Nordic Laser Materials Processing Conference, Nolamp, Lappeenranta, Finland, 25 Aug 2015 - 28 Aug 2015; Amsterdam [u.a.] : Elsevier, Physics procedia, 78, 99-109 (2015). doi:10.1016/j.phpro.2015.11.022, Published by Elsevier, Amsterdam [u.a.]
- Published
- 2015
- Full Text
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47. Analysis of moving surface structures at a laser-induced boiling front
- Author
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Alexander Kaplan and Ramiz Matti
- Subjects
Brightness ,Materials science ,Laser ablation ,business.industry ,Front (oceanography) ,General Physics and Astronomy ,Laser beam welding ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Laser ,Surfaces, Coatings and Films ,law.invention ,Optics ,law ,Boiling ,business ,Keyhole ,Laser drilling - Abstract
Recently ultra-high speed imaging enabled to observe moving wave patterns on metal melts that experience laser-induced boiling. In laser materials processing a vertical laser-induced boiling front governs processes like keyhole laser welding, laser remote fusion cutting, laser drilling or laser ablation. The observed waves originate from temperature variations that are closely related to the melt topology. For improved understanding of the essential front mechanisms and of the front topology, for the first time a deeper systematic analysis of the wave patterns was carried out. Seven geometrical shapes of bright or dark domains were distinguished and categorized, in particular bright peaks of three kinds and dark valleys, often inclined. Two categories describe special flow patterns at the top and bottom of the front. Dynamic and statistical analysis has revealed that the shapes often combine or separate from one category to another when streaming down the front. The brightness of wave peaks typically fluctuates during 20–50 μs. This variety of thermal wave observations is interpreted with respect to the accompanying surface topology of the melt and in turn for governing local mechanisms like absorption, shadowing, boiling, ablation pressure and melt acceleration. The findings can be of importance for understanding the key process mechanisms and for optimizing laser materials processing.
- Published
- 2014
48. An investigation on stability of laser hybrid arc welding
- Author
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Jan Frostevarg, Alexander Kaplan, Majid Ghoreishi, and Mahmoud Moradi
- Subjects
Heat-affected zone ,Materials science ,Mechanical Engineering ,Laser beam welding ,Electrogas welding ,Welding ,Electric resistance welding ,Atomic and Molecular Physics, and Optics ,Arc blow ,Electronic, Optical and Magnetic Materials ,law.invention ,Plasma arc welding ,law ,Arc welding ,Electrical and Electronic Engineering ,Composite material - Abstract
The stability of the weld surface quality resulting from laser–arc hybrid welding of 4 mm thick steel was studied. The trends of stability in terms of top weld width variation were estimated by usi ...
- Published
- 2013
49. Analysis of the stress raising action of flaws in laser clad deposits
- Author
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T. Peltola, Zuheir Barsoum, Petri Vuoristo, Alexander Kaplan, Minhaj M Alam, Juha Miettinen, J. Poutala, J. Junkala, Jonne Näkki, and Jari Tuominen
- Subjects
Fatigue cracking ,Materials science ,business.industry ,Physics::Optics ,General Medicine ,Structural engineering ,Laser ,Raising (metalworking) ,Finite element method ,Action (physics) ,law.invention ,Computer Science::Robotics ,Stress (mechanics) ,law ,business ,Stress concentration - Abstract
Fatigue cracking of laser clad cylindrical and square section bars depends upon a variety of factors. This paper presents Finite Element Analysis (FEA) of the different macro stress fields generate ...
- Published
- 2013
50. Guidelines in the Choice of Parameters for Hybrid Laser Arc Welding with Fiber Lasers
- Author
-
Alexander Kaplan, Ingemar Eriksson, and John Powell
- Subjects
Materials science ,Fiber laser ,Laser beam welding ,Mechanical engineering ,Welding ,Physics and Astronomy(all) ,Laser ,Hybrid ,Gas metal arc welding ,law.invention ,High speed imaging ,law ,GMAW ,Welding power supply ,Laser-hybrid welding ,Manufacturing, Surface and Joining Technology ,Arc welding ,Bearbetnings-, yt- och fogningsteknik - Abstract
Laser arc hybrid welding has been a promising technology for three decades and laser welding in combination with gas metal arc welding (GMAW) has shown that it is an extremely promising technique. On the other hand the process is often considered complicated and difficult to set up correctly. An important factor in setting up the hybrid welding process is an understanding of the GMAW process. It is especially important to understand how the wire feed rate and the arc voltage (the two main parameters) affect the process. In this paper the authors show that laser hybrid welding with a 1 μm laser is similar to ordinary GMAW, and several guidelines are therefore inherited by the laser hybrid process. Validerad; 2013; 20130410 (andbra); Konferensartikel i tidskrift
- Published
- 2013
- Full Text
- View/download PDF
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