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. / In recent years, an extensive effort has been made to leap European aviation towards more sustainable transportation. Conventional manufacturing methods used in aerospace industry require significant amounts of raw materials, whose extraction, processing, and utilization have adverse environmental impacts. Thus, there is a strong motivation to develop novel, more material efficient fabrication methods. Additive Manufacturing (AM), also known as 3D-printing, offers the advantage of manufacturing near-net-shape structures by adding material only where it is needed, minimizing waste, and improving material efficiency. However, introducing AM fabricated structures as components in safety-critical aerospace systems poses a significant challenge due to the inherent complexity of AM processes. This complexity can result in variations that may lead to defects or inconsistencies in the fabricated structures. Thus, increasing automation by developing in-process monitoring, and control solutions is the vital step to reach the necessary reliability and repeatability. This thesis presents development towards multi-sensor monitoring and control of Directed Energy Deposition (DED) using a Laser Beam (LB). DED-LB is an advanced technology that allows to manufacture large-scale, near-net-shape metallic parts. In this work, in-process monitoring solutions for DED-LB with feedstock powder and wire were investigated. The set-up of the latter was complemented by resistive pre-heating of the feedstock wire (hot-wire) which provided means of fine-tuning the heat input and improving metal fusion. Formonitoring purposes, three different in-situ techniques were investigated to monitor process stability and variability. Machine vision and electrical sensing were utilized during DED-LB with feedstock wire (DED-LB/w) depositions,while optical emission spectroscopy was used for monitoring processes with feedstock powder (DED-LB/p) as well as wire. A multi-sensorsystem based on the three sensing technologies was tested during DED-LB/w depositions. The vision system gave clear indications of variations from nominal conditions. Voltage and current sensors indications correlated to changes in process parameters and reflected well the metal transfer (liquid bridge) condition.The spectrometer system indicated well changes related to heat input. In addition, analysis of obtained spectra allowed to detect losses of vital alloying element during DED-LB/p. The main conclusion from the results underlines the need for simultaneous multi-sensor monitoring as it allows not only to detect and estimate process changes but also to better interpret their root causes. Such setup will positively enable a future robust, fault tolerant control system. / <p>Paper 3 is under acception but included in this thesis with CC BY-license.</p>

A study and analysis of high energy laser (HEL) systems aboard tactical aircraft is performed. The FA-18E/F Hornet and F-35 Joint Strike Fighter (JSF), equipped with solid-state HEL systems, are the main subjects of the study. Considerations of power generation and thermal management for a fighter-sized HEL system and aero-optic effects on beam propagation from high and medium altitude platforms are examined. An overview of system capabilities details how the HEL system will be more difficult to incorporate into legacy strike aircraft, but may be feasible for future aircraft such as the JSF. Tactical flight simulations are used to study and develop potential concepts of operation (CONOPS), using realistic scenarios and threat environments. Results show that a tactical HEL will not be a stand-alone weapon in combat, but will have many potentially useful tactical applications. Another study of a high energy free electron laser (FEL) system aboard C-130J-30 Hercules shows that such a system is feasible. Finally, a study of the FEL shows that strong field extraction can be optimized using undulator tapering. / US Marien Corps (USMC) author.

Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2003. / Thesis advisor(s): William Colson, Robert Armstead. Includes bibliographical references (p. 67-68). Also available online.

Thesis (M.S. in Applied Physics)--Naval Postgraduate School, June 2005. / Thesis Advisor(s): William B. Colson. Includes bibliographical references (p. 79-81). Also available online.

Laser-based additive manufacturing is inherently associated with extreme, unprecedented, and rapid thermokinetics which impact the microstructural evolution in a built component. Such a unique, near to non-equilibrium microstructure/phase evolution in laser additively manufactured metallic components impact their properties in engineering application. In light of this, the present work investigates the unique microstructural traits as a result of process induced spatial and temporal variation in thermokinetic parameters in laser directed energy deposited CoCrMo biomedical alloy. The influence of such a unique microstructural evolution in laser directed energy deposited CoCrMo on electrochemical response in physiological media was elucidated and compared with a conventionally manufactured, commercially available CoCrMo component. Furthermore, while investigation of the electrochemical response, such a microstructural evolution in laser directed energy deposited CoCrMo led to in-situ surface modification of the built components in physiological media via selective, non-uniform electrochemical etching. Such in-situ surface modification resulted in enhanced biocompatibility in terms of mammalian cell growth, cell-substrate adhesion, blood compatibility, and antibacterial properties indicating improved osteointegration, compared to a conventionally manufactured, commercially available CoCrMo component.

High-power fiber lasers have emerged as a cornerstone in the realm of laser technology. Characterized by their exceptional efficiency, ruggedness, and versatility, fiber lasers are experiencing widespread use in manufacturing, medical, defense, science, and in long range sensing. Unfortunately, high-power applications require strict spatial and spectral performance characteristics to be maintained, which has yet to be perfected. This dissertation discusses the power scaling of ytterbium-doped fiber laser amplifiers, presenting three significant advancements. First, a novel photonic lantern-based method is introduced for real-time monitoring of laser beam modal content and beam quality. Initial tests highlight the photonic lantern's efficiency in predicting the onset of modal instability while simultaneously measuring the laser's output beam quality, M2. Second, this work achieved 2.2 kW single-mode narrow-linewidth laser delivery through a 5-tube nested antiresonant hollow core fiber, maintaining over 95% transmission efficiency and near diffraction-limited beam quality. Lastly, this research explores active-gain fiber designs to mitigate nonlinear effects for further power scaling. One design employing confined-doping strategies, achieving a 2.4x increase in the maximum output power before the onset of stimulated Brillouin scattering. Additionally, a second experiment employing a bend-insensitive fiber design demonstrated a transverse modal instability threshold nearly 3x that of its step-index counterpart. Collectively, this work presents a novel approach to power scale, deliver, and monitor multi-kW Yb-doped fiber laser amplifiers enabling the next-generation of applications requiring the strictest spatial and spectral performance.

No description available.

Laser-Directed Energy Deposition (L-DED), an Additive Manufacturing (AM) processused for the fabrication of parts in a layer-wise approach has displayed an immense potential over the last decade. The aerospace industry stands as the primary beneficiary due to the L-DED process capability to build near-net-shape components with minimal tooling and thereby producing minimum wastage because of reduced machining. The widespread use of Alloy 718 in the aero-engine application has prompted huge research interest in the development of L-DED processing of this superalloy. AM processes are hindered by low build rates and high cycle times which directly affects the process costs. To overcome these issues, the present work focusses on obtaining high deposition rates through a high material feed. Studying the influence of process parameters during the L-DED process is of prime importance as they determine the performance of in-service structures. In the present work, process parameters such as laser power, scanning speed, feed rate and stand-offdistances are varied and their influence on geometry and microstructure of Alloy 718 single-track deposits are analyzed. The geometry of deposits is measured in terms of height, width and depth; and the powder capture efficiency is determined by measuring areas of deposition and dilution. The microstructure of the deposits shows a column ardendritic structure in the middle and bottom region of the deposits and equiaxed grains in the top region. Nb-rich segregation involving laves and NbC phases, typical of Alloy718 is found in the interdendritic regions and grain boundaries. The segregation increases along the height of the deposit with the bottom region having the least and the top region showing the highest concentration of Nb-rich phases due to the variation in cooling rates. A high laser power (1600 W – 2000 W) and a high scanning speed (1100 mm/min) are found to be the preferable processing conditions for minimizing segregation. Another approach to minimize segregation is by performing post-build heat treatments. The solution treatment (954 °C/1 hr) and double aging (718 °C/8 hr + 621 °C/ 8 hr) standardized for the wrought form of Alloy 718 is applied to as-built deposits which showed a reduction in segregation due to the dissolution of Nb-rich phases. Upon solution treatment, this reduction is accompanied by precipitation of the delta phase, found predominantly in top and bottom regions and sparsely in the middle region of the deposit.

No description available.

No description available.