| 1. |
- Ancona, Antonio, 1974-, et al.
(författare)
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Monitoring and control of directed energy deposition using a laser beam
- 2023. - 1.
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Ingår i: Additive Manufacturing of High-Performance metallic Materials. - : Elsevier. - 9780323918855 - 9780323913829 ; , s. 612-638
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Bokkapitel (refereegranskat)abstract
- To be a successful competitor among other technologies, metallic laser-directed energy depositionusing a laser beam would benefit from the support of intelligent automation making the processrobust, repeatable, and cost-efficient. This calls for technology leaps towards robust and accuratedetection and estimation of the conditions during processing and control schemes for robustperformance. This chapter discusses how developments in sensor technology and model-basedsignal processing can contribute to advancements in in-process monitoring of directed energydeposition using a laser beam and how developments in model-based feedforward- and feedbackcontrol can support automation. The focus is on how machine vision, optical emission spectroscopy,thermal sensing, and electrical process signals can support monitoring, control and better processunderstanding. These approaches are industrially relevant and have a high potential to support amore sustainable manufacturing.
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| 2. |
- Kisielewicz, Agnieszka, et al.
(författare)
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Hot-Wire Laser-Directed Energy Deposition : Process Characteristics and Benefits of Resistive Pre-Heating of the Feedstock Wire
- 2021
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Ingår i: Metals. - : MDPI. - 2075-4701. ; 11:4, s. 1-25
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the influence of resistive pre-heating of the feedstock wire (here called hot-wire) on the stability of laser-directed energy deposition of Duplex stainless steel. Data acquired online during depositions as well as metallographic investigations revealed the process characteristic and its stability window. The online data, such as electrical signals in the pre-heating circuit and images captured from side-view of the process interaction zone gave insight on the metal transfer between the molten wire and the melt pool. The results show that the characteristics of the process, like laser-wire and wire-melt pool interaction, vary depending on the level of the wire pre-heating. In addition, application of two independent energy sources, laser beam and electrical power, allows fine-tuning of the heat input and increases penetration depth, with little influence on the height and width of the beads. This allows for better process stability as well as elimination of lack of fusion defects. Electrical signals measured in the hot-wire circuit indicate the process stability such that the resistive pre-heating can be used for in-process monitoring. The conclusion is that the resistive pre-heating gives additional means for controlling the stability and the heat input of the laser-directed energy deposition.
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| 3. |
- Kisielewicz, Agnieszka, et al.
(författare)
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In-process spectroscopic detection of chromium loss during Directed Energy Deposition of alloy 718
- 2020
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Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 186
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a fast optical spectrometer was used to monitor the Directed Energy Deposition (DED) process, during the deposition of Alloy 718 samples with different laser power, thus different energy inputs into the material. Spectroscopic measurements revealed the presence of excited Cr I atoms in the plasma plume. The presence was more apparent for the samples characterized by higher energy input. The Cr depletion from these samples was confirmed by lower Cr content detected by Energy-Dispersive X-ray Spectroscopy (EDS) analysis. The samples were also characterized by higher oxidation and high-temperature corrosion rates in comparison to the samples produced with low energy input. These results prove the applicability of an optical emission spectroscopic system for monitoring DED to identify process conditions leading to compositional changes and variation in the quality of the built material.
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| 4. |
- Kisielewicz, Agnieszka, et al.
(författare)
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Multi sensor monitoring of the wire-melt pool interaction inhot-wire directed energy deposition using laser beam
- 2023
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Ingår i: IOP Conference Series. - : IOP Publishing. ; , s. 1-11
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Konferensbidrag (refereegranskat)abstract
- This study investigates the combination of three sensors to improve in-process monitoring of the liquid bridge between the feedstock wire and melt pool in hot-wire Directed Energy Deposition using Laser Beam. The stability of the deposition process relies on the transfer of metal between the molten feedstock wire and melt pool. Therefore, monitoring the condition of the liquid bridge and the interaction between the feedstock wire and melt pool is crucial. By utilizing a laser-optics-integrated visible range optical spectrometer and electrical sensors measuring voltage and current, relevant process changes and indications of instabilities were detected. Combined information from the current sensor and the spectrometer provided a better understanding of the process and helped to identify deviations leading to unstable deposition modes.
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| 5. |
- Kisielewicz, Agnieszka, et al.
(författare)
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Spectroscopic monitoring of laser blown powder directed energy deposition of Alloy 718
- 2018
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Ingår i: Procedia Manufacturing. - : Elsevier BV. - 2351-9789. ; 25, s. 418-425
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Tidskriftsartikel (refereegranskat)abstract
- Experimental explorations of a spectrometer system used for in-process monitoring of the laser blown powder directed energy deposition of Alloy 718 is presented. Additive manufacturing of metals using this laser process experiences repeated heating and cooling cycles which will influence the final microstructure and chemical composition at every given point in the built. The spectrometer system disclosed, under certain process conditions, spectral lines that indicate vaporisation of chromium. Post process scanning electron microscope energy dispersive spectroscopy analysis of the deposited beads confirmed a reduction of chromium. Since the chromium concentration in Alloy 718 is correlated to corrosion resistance, this result encourages to further investigations including corrosion tests.
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| 6. |
- Kisielewicz, Agnieszka
(författare)
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Towards multi-sensor monitoringand control of Directed Energy Deposition using a Laser Beam
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Under senare år har omfattande insatser gjorts för att främja mer hållbara flygtransporter i Europa. De konventionella tillverkningsmetoderna som används inom flyg- och rymdindustrin kräver betydande mängder råmaterial, vars utvinning, bearbetning och användning har negativa miljöeffekter. Därför finns det ett starkt incitament att utveckla nya, mer material-effektiva tillverkningsmetoder.Additiv tillverkning (AM), även känd som 3D-printining, har fördelen att direkt komma nära den slutliga formen på strukturer genom att lägga till material endast där det behövs, något som minimerar spill och förbättrar materialanvändningen. Dock utgör införandet av AM komponenter i säkerhetskritiska flyg- och rymdtillämpningar en betydande utmaning på grund av komplexiteten hos processerna. Denna komplexitet kan leda till tillverkningsvariationer som i sin tur kan resultera i defekter i de tillverkade strukturerna. Därför är framsteg inom automation genom utvecklingen av lösningar för övervakning och styrning under processens gång ett nödvändigt steg för att uppnå tillräcklig pålitlighet och repeterbarhet.Denna avhandling presenterar en utveckling av multisensorövervakning och styrning av Directed Energy Deposition (DED) med en laservärmekälla (LB). DED-LB är en avancerad teknik som möjliggör tillverkning av storskaliga metallkomponenter nära den slutliga formen. I detta arbete har lösningar undersökts för övervakning av DED-LB med tillsatspulver och tråd. För fallet med tillsatstråd kan denna kompletteras med resistiv förvärmning (så kallad hotwire), vilket ger möjlighet att ytterligare finjustera värmetillförseln och förbättra smältprocessen. För övervakningsändamål undersöktes tre olika in-situtekniker för processens stabilitet och varians. Maskinseende och elektriska givare användes för DED-LB med tillsatstråd (DED-LB/w), medan optisk spektroskopi användes för övervakning både av processen med tillsatspulver (DEDLB/p) samt med tråd. Ett multisensorsystem baserat på de tre teknologierna testades för DED-LB/w. Det kamerabaserade systemet gav tydliga indikationer på avvikelser från nominella processförhållanden.Spännings-och strömgivarnas signaler korrelerade med förändringar i processparametrar och återspeglade tydligt metallöverföringen. Spektrometersystemet indikerade förändringar relaterade till värmeöverföringen. Dessutom möjliggjorde analysen av erhållna spektra en detektering av förluster av viktiga legeringselement under DED-LB/p.Slutsatsen från resultaten understryker behovet av multisensorövervakning, eftersom det inte bara möjliggör detektering och skattning av processförändringar utan även en bättre förståelse av deras grundorsaker. Den presenterade ansatsen är ett viktigt bidrag i utvecklingen av ett framtida robust och feltolerant automatiskt styrsystem.
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| 7. |
- Noori Rahim Abadi, Seyyed Mohammad Ali, 1985-, et al.
(författare)
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Influence of laser-wire interaction on heat and metal transfer in directed energy deposition
- 2023
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310 .- 1879-2189. ; 205
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Tidskriftsartikel (refereegranskat)abstract
- In this study, laser metal fusion with feedstock wire is addressed. We investigated how various process parameters affect the fraction of beam energy that is absorbed by the wire and the workpiece and the metal transfer from the feedstock wire to the melt pool. To perform this research, a thermo-fluid dynamic model with tracking of free surface deformation was developed to include the feeding of a solid wire and predict its melting. The fraction of beam energy absorbed by the metal was modeled as a function of local surface curvature and temperature, accounting for multiple Fresnel reflections and absorptions. The model was applied to Titanium alloy (Ti-6Al-4V) with a 1.07 μm laser and a process in conduction mode. Experiments at various wire feeding rates were conducted to evaluate the model’s ability to predict the process and a good agreement was obtained. The different parameters studied were the beam angular position, the wire angular position, the wire feed rate, and the beam-wire offset. The analysis of the simulation results gave a detailed physical understanding of the laser energy use. It highlighted that thermocapillary and Rayleigh-Plateau instabilities can contribute to the transition from continuous to drop metal transfer mode. Damping these instabilities might thus allow using a wider process window.
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| 8. |
- Valiente Bermejo, María Asunción, 1972-, et al.
(författare)
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Microstructure of laser metal deposited duplex stainless steel : Influence of shielding gas and heat treatment
- 2021
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Ingår i: Welding in the World. - : Springer. - 0043-2288 .- 1878-6669. ; 65, s. 525-541
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Tidskriftsartikel (refereegranskat)abstract
- This research work is the first step in evaluating the feasibility of producing industrial components by using Laser Metal Deposition with duplex stainless steel Wire (LMDw). The influence of Ar and N2 shielding gases was investigated in terms of nitrogen loss and in the microstructure and austenite content of different deposited geometries. The evolution of the microstructure in the build-up direction of the Ar and N2-shielded blocks was compared in the heat-treated and as-deposited conditions. The susceptibility for oxygen pick-up in the LMDw deposits was also analyzed, and oxygen was found to be in the range of conventional gas-shielded weldments. Nitrogen loss occurred when Ar-shielding was used; however, the use of N2-shielding prevented nitrogen loss. Austenite content was nearly doubled by using N2-shielding instead of Ar-shielding. The heat treatment resulted in an increase of the austenite content and of the homogeneity in the microstructure regardless of the shielding gas used. The similarity in microstructure and the low spread in the phase balance for the as-deposited geometries is a sign of having achieved a stable and consistent LMDw process in order to proceed with the build-up of more complex geometries closer to industrial full-size components.
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