Dissertations / Theses on the topic 'Directed Energy Deposition Additive Manufacturing'

Les procédés de fabrication additive laser par dépôt de poudre offrent une opportunité unique pour la fabrication de grandes pièces à géométrie complexe. Cependant, les déformations mécaniques induites par ces procédés entrainent des défauts pouvant conduire à des pièces rebutées. Au cours de cette thèse, différents modèles ont donc été développés pour mieux comprendre l’apparition de ces déformations en fonction des paramètres opératoires. Un premier modèle thermomécanique prédit le comportement élastoplastique lors de la construction d’un mur en acier inoxydable 316L. L’apport de chaleur est modélisé par une source double ellipsoïdale mobile et la construction des couches se fait à l’aide d’une méthode hybride « Quiet/Active élément ». Un écrouissage isotrope non linéaire est considéré, avec prise en compte de la restauration d’écrouissage à hautes températures. Afin de réduire drastiquement les temps de calcul, une nouvelle source de chaleur est proposée utilisant une source ellipsoïdale allongée qui moyenne l’énergie sur un intervalle d’espace et de temps. Cependant, un intervalle d’espace trop grand diminue la précision du modèle. De nouveaux paramètres sont alors introduits afin d’identifier le meilleur compromis entre temps de calcul et précision. L’ensemble des modèles proposés est confronté avec succès avec des données expérimentales en termes de température et déplacement et ce pour différents paramètres opératoires. Enfin, des modèles multi-échelles basés l’activation par couche ou les méthodes de déformations inhérentes sont étudiés en vue de réduire les temps de calcul
Directed Energy Deposition (DED) Additive Manufacturing technology offers a unique possibility of fabricating large-scale complex-shape parts. However, process-induced deformation in the fabricated part is still a big obstacle in successfully fabricating large-scale parts. Therefore, multiple numerical models have been developed to understand the accumulation of induced deformation in the fabricated part. The first model predicts the thermo-elastoplastic behaviour that captures the laser movement. The laser-material interaction and metal deposition are modeled by employing a double ellipsoid heat source and the Quiet/Active material activation method respectively. The model considers isotropic non-linear material hardening to represent actual metal behaviour. It also employs an instantaneous stress relaxation model to simulate the effects of physical phenomena like annealing, solid-state phase transformation, and melting. Using this model as a reference case, an efficient model is developed with an objective to reduce the computation time and make it feasible to simulate large-part. The model employs an Elongated Ellipsoid heat source that averages the heat source over the laser path which reduces the computational burden drastically. However, averaging over large laser path results in inaccurate results. Therefore, new parameters are developed that identify the best compromise between computation time reduction and accuracy. Both models are validated with experimental data obtained from several experiments with different process parameters. Finally, other Multi- scale methods such as the Layer-by-layer method and Inherent Strain-based methods are implemented and explored

In recent years, additive manufacturing (AM) of Alloy 718 has received increasing interest in the field of manufacturing engineering owing to its attractive features compared to those of conventional manufacturing methods. The ability to produce complicated geometries, low cost of retooling, and control of the microstructure are some of the advantages of the AM process over traditional manufacturing methods. Nevertheless, during the building process, the build material undergoes complex thermal conditions owing to the inherent nature of the process. This results in phase transformation from liquid to solid and solid state. Thus, it creates microstructural gradients in the built objects, and as a result,heterogeneous material properties. The manufacturing process, including the following heat treatment that is used to minimise the heterogeneity, will cause the additively manufactured material to behave differently when compared to components produced by conventional manufacturing methods. Therefore, understanding the microstructure formation during the building and subsequent post-heat treatment is important, which is the objective of this work. Alloy 718 is a nickel-iron based super alloy that is widely used in the aerospace industry and in the gas turbine power plants for making components subjected tohigh temperatures. Good weldability, good mechanical properties at high temperatures, and high corrosion resistance make this alloy particularly suitablefor these applications. Nevertheless, the manufacturing of Alloy 718 components through traditional manufacturing methods is time-consuming and expensive. For example, machining of Alloy 718 to obtain the desired shape is difficult and resource-consuming, owing to significant material waste. Therefore, the application of novel non-conventional processing methods, such as AM, seems to be a promising technique for manufacturing near-net-shape complex components.In this work, microstructure modelling was carried out by using multiphase-field modelling to model the microstructure evolution in electron beam melting (EBM) and laser metal powder directed energy deposition (LMPDED) of Alloy 718 and x subsequent heat treatments. The thermal conditions that are generated during the building process were used as input to the models to predict the as-built microstructure. This as-built microstructure was then used as an input for the heat treatment simulations to predict the microstructural evolution during heat treatments. The results showed smaller dendrite arm spacing (one order of magnitude smaller than the casting material) in these additive manufactured microstructures, which creates a shorter diffusion length for the elements compared to the cast material. In EBM Alloy 718, this caused the material to have a faster homogenisation during in-situ heat treatment that resulting from the elevated powder bed temperature (> 1000 °C). In addition, the compositional segregation that occurs during solidification was shown to alter the local thermodynamic and kinetic properties of the alloy. This was observed in the predicted TTT and CCT diagrams using the JMat Pro software based on the predicted local segregated compositions from the multiphase-field models. In the LMPDED Alloy 718 samples, this resulted in the formation of δ phase in the interdendritic region during the solution heat treatment. Moreover, this resulted in different-size precipitation of γ'/γ'' in the inter-dendritic region and in the dendrite core. Themicro structure modelling predictions agreed well with the experimental observations. The proposed methodology used in this thesis work can be an appropriate tool to understand how the thermal conditions in AM affect themicro structure formation during the building process and how these as-built microstructures behave under different heat treatments.

Studio condotto presso il Dipartimento di Ingegneria Industriale dell’Università di Bologna su un processo di Laser Direct Energy Deposition, o Laser Cladding, e sulla sua caratterizzazione, avente come fine ultimo quello di realizzare pezzi massicci a base rettangolare dotati di una morfologia esterna regolare e al contempo privi di difetti macroscopici all’interno, quali porosità o zone con mancata fusione del materiale d’apporto. Nella prima parte dello studio sono stati presi in esame i principali parametri di processo, ovvero la potenza della sorgente laser e la portata di polvere, e l’influenza che essi hanno sulle caratteristiche geometriche del deposito (profondità di penetrazione, altezza, larghezza, grado di diluizione, area del deposito e del rinforzo, ampiezza media della ZTA, percentuale di porosità). Tale studio si è basato sull’osservazione ed analisi al microscopio di singoli cordoni di deposizione, realizzati variando la portata di polvere la potenza del laser, a parità di velocità di avanzamento. La seconda parte si basa sull’analisi dei risultati delle prove condotte con lo scopo di realizzare dei campioni massicci a base rettangolare: si sono studiati gli effetti che variazioni dei parametri di processo e della strategia di scansione hanno avuto sulla morfologia finale dei pezzi e sulle loro caratteristiche interne (porosità, zone con mancata fusione). Si sono confrontate due strategie di deposizione, la strategia con ritorno della testa a laser spento (laser OFF) e la strategia con ritorno della testa a laser acceso (laser ON). Tale studio ha permesso di concludere che la strategia con ritorno laser ON risulta essere preferibile in quanto non solo consente di ottenere un risparmio in termini energetici, di tempo e di quantità di polvere utilizzata, ma anche di realizzare dei pezzi massicci che rappresentano il miglior compromesso ottenuto tra una morfologia esterna uniforme e delle buone caratteristiche interne, con una densità prossima al 100%.

Wire and Arc Additive Manufacturing is a novel Additive Manufacturing technology. As a result, the process for progressing from a solid model to manufacturing code, i.e. the Part Programming process, is undeveloped. In this report the Part Programming process, unique for Wire and Arc Additive Manufacturing, has been investigated to answer three questions; What is the Part Programming process for Wire and Arc Additive Manufacturing? What are the requirements on the Part Programming process? What software can be used for the Part Programming process? With a systematic review of publications on Wire and Arc Additive Manufacturing and related subjects, the steps of the Part Programming process and its requirements have been clarified. The Part Programming process has been used for evaluation of software solutions, resulting in multiple recommendations for implemented usage. Verification of assumptions, made by the systematic review, has been done by physical experiments to give further credibility to the results.

In der vorliegenden Arbeit wird ein Maschinenkonzept präsentiert, welches für die Additive Fertigung von großvolumigen Titanbauteilen speziell entwickelt wurdet. Hierbei wird mit den Direct-Energy_Deposition Verfahren das Bauteil in einer separaten Inertgasatmosphäre erzeugt. Zur Führung der Prozesstechnik soll erstmals ein Roboter verwendet werden, der ebenfalls in dieser Atmosphäre verbaut ist. Dieser ist allerdings schwierigen Bedingungen ausgesetzt, da die Spannungsfestigkeit sowie die Isolationsschwelle in Argon im Vergleich zu Luft drastisch reduziert sind.

Additive manufacturing (AM) is a quickly rising method of manufacturing due to its ability to increase design freedom. This allows the manufacturing of components not possible by traditional subtractive manufacturing. AM can greatly reduce lead time and material waste, therefore decreasing the cost and environmental impact. The adoption of AM in the aerospace industry requires strict control and predictability of the material deposition to ensure safe flights.  The method of AM for this thesis is Laser Metal Deposition with wire (LMD-w). Using wire as a feedstock introduces a potential problem, the material transfer from the wire to the substrate. This requires all process parameters to be in balance to produce a stable deposition. The first sign of unbalanced process parameters are the material transfer stabilities; stubbing and dripping. Stubbing occurs when the energy to melt the wire is too low and the wire melts slower than required. Dripping occurs when too much energy is applied and the wire melts earlier than required.  These two reduce the predictability and stability that is required for robust manufacturing.  Therefore, the use of thermal simulations to predict the material transfer stability for LMD-w using Waspaloy as the deposition material has been studied.  It has been shown that it is possible to predict the material transfer stability using thermal simulations and criterions based on preexisting experimental data. The criterion for stubbing checks if the completed simulation result produces a wire that ends below the melt pool. For dripping two criterions shows good results, the dilution ratio is a good predictor if the tool elevation remains constant. If there is a change in tool elevation the dimensionless slenderness number is a better predictor.  Using these predictive criterions it is possible to qualitatively map the process window and better understand the influence of tool elevation and the cross-section of the deposited material.
Additiv tillverkning (AT) är en kraftigt växande tillverkningsmetod på grund av sin flexibilitet kring design och möjligheten att skapa komponenter som inte är tillverkningsbara med traditionell avverkande bearbetning.  AT kan kraftigt minska tid- och materialåtgång och på så sett minskas kostnader och miljöpåverkan. Införandet av AT i flyg- och rymdindustrin kräver strikt kontroll och förutsägbarhet av processen för att försäkra sig om säkra flygningar.  Lasermetalldeponering av tråd är den AT metod som hanteras i denna uppsats. Användandet av tråd som tillsatsmaterial skapar ett potentiellt problem, materialöverföringen från tråden till substratet. Detta kräver att alla processparametrar är i balans för att få en jämn materialöverföring. Är processen inte balanserad syns detta genom materialöverföringsstabiliteterna stubbning och droppning. Stubbning uppkommer då energin som tillförs på tråden är för låg och droppning uppkommer då energin som tillförs är för hög jämfört med vad som krävs för en stabil process. Dessa två fenomen minskar möjligheterna för en kontrollerbar och stabil tillverkning.  På grund av detta har användandet utav termiska simuleringar för att prediktera materialöverföringsstabiliteten för lasermetalldeponering av tråd med Waspaloy som deponeringsmaterial undersökts. Det har visat sig vara möjligt att prediktera materialöverföringsstabiliteten med användning av termiska simuleringar och kriterier baserat på tidigare experimentell data. Kriteriet för stubbning kontrolleras om en slutförd simulering resulterar i en tråd som når under smältan.  För droppning finns två fungerande kriterier, förhållandet mellan svetshöjd och penetrationsdjup om verktygshöjden är konstant, sker förändringar i verktygshöjden är det dimensionslös ”slenderness” talet ett bättre kriterium.  Genom att använda dessa kriterier är det möjligt att kvalitativt kartlägga processfönstret och skapa en bättre förståelse för förhållandet mellan verktygshöjden och den deponerade tvärsnittsarean.

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.

Additive Manufacturing (AM) by Directed Energy Deposition-arc (DED-arc) is competing with other AM technologies due to its high deposition rate, ability to produce large parts with medium/high geometric complexity and low capital and running costs. However, residual stresses, coarse microstructures, and defects on parts, such as cracks and pores, may compromise in-service industrial applications and need to be overcome. This work aimed to develop and validate two innovative process variants: one based on in-situ hot forging; and the other on temperature control, that is, indirect cooling of deposited material and hot forging. The hot forging variant consisted of locally forging the deposited layer at high temperatures using low forces. The goal is to create an uniform plastic deformation zone along the layer, to promote grain refinement, reduce material anisotropy and collapse defects. The variant based on temperature control consisted of cooling the hammer components and the shielding gas used to protect the molten pool, to increase the solidification rate and thus, prevent grain coalescence. For this, dedicated DED-arc equipment was designed and manufactured with specific features for research. The effect of hot forging was analysed in detail on 316LSi stainless steel, and the feasibility of its application was verified in other relevant industrial materials. It was concluded that hot forging can induce dynamic recrystallization, increase nucleation sites and prevent epitaxial grain growth. Thus, it contributes to an overall refined and homogeneous microstructure with improved mechanical properties. The developed cooling system lowered the average temperature of the nozzle and hammer during consecutive depositions. Cooling of the shielding gas had no major effect on the cooling rates and microstructure of the materials, however, it was observed that the hot forging changes the heat flow conditions of the part, promoting higher cooling rates.
A tecnologia de deposição direta de energia por arco (DED-arc) tem competido com outras tecnologias de fabrico aditivo devido à sua elevada taxa de deposição, capacidade de produzir componentes de grandes dimensões com média/alta complexidade geométrica e baixos custos de implementação e funcionamento. Contudo, as elevadas tensões residuais, as microestruturas grosseiras, ou os defeitos do tipo poros, podem comprometer algumas aplicações industriais e necessitam de ser superados. Este trabalho visou desenvolver e validar duas variantes inovadoras de processo DED- arc: uma baseada no forjamento a quente; e outra no controlo de temperatura. A variante baseada no forjamento, consistiu em forjar o material depositado imediatamente após a deposição, utilizando baixas forças. O objetivo foi a produção de uma zona de deformação plástica uniforme ao longo de cada camada, para promover alterações microestruturais, nomeadamente o refinamento dos grãos e a redução da anisotropia. A variante baseada no trabalho termodinâmico consistiu em arrefecer os componentes do martelo e o gás utilizado para proteger o banho de fusão, com o objetivo de aumentar a taxa de arrefecimento e assim evitar a coalescência dos grãos. Neste sentido, foi concebido e fabricado um equipamento de DED-arc, com características específicas para investigação. O efeito do forjamento a quente foi estudado detalhadamente no aço inoxidável 316LSi, e foi verificada a viabilidade da sua aplicação noutros materiais relevantes industrialmente. Concluiu-se que o forjamento induz recristalização dinâmica, aumenta os pontos de nucleação e impede o crescimento de grãos epitaxiais, contribuindo para uma microestrutura globalmente mais fina, homogénea e com melhores propriedades mecânicas. O sistema de arrefecimento desenvolvido baixou a temperatura do bocal e do martelo durante as deposições consecutivas. O arrefecimento do gás de proteção não teve efeito nas taxas de arrefecimento nem na microestrutura do material, contudo, observou-se que o forjamento altera as condições de fluxo de calor, promovendo taxas de arrefecimento maiores.

Additive manufacturing (AM) provides unique opportunities to push the boundaries of material properties and free form fabrication. However with this novel manufacturing technique a number of defects not commonly found in conventional processes such as machining or casting can arise. Both experimental and numerical studies can help better understand the printed material on a more fundamental level in order to optimize the process and mitigate these defects. Electron microscopy can provide essential information about the as-built microstructure and characteristic defects while numerical modelling can help determine a correlation between process parameters and the resulting properties. First, an initial investigation of directed energy deposition (DED) processed 4140 steel was conducted using various microscopy methods to better understand the defects and microstructure of the printed alloy. A martensite dominate microstructure within a bainitic matrix with increasing degrees of tempering further down the build was revealed. Additional sample preparation was conducted with a focused ion beam and analyzed with the transmission electron microscope to investigate features such as grain boundaries, mechanical twins and interplanar spacing. This interplanar spacing was measured for a number of different diffraction images and compared with the theoretical values. The deviation between the measured and theoretical values can be attributed to defects such as residual stress which causes lattice strain and consequently a smaller or larger spacing between atomic planes. Lastly, diffraction images were characterized and compared with the literature to determine the Miller indices and the specific zone axis orientations. A thermo-mechanical-metallurgical finite element model for 42CrMo4 steel was then developed in ABAQUS to identify the correlation between processing parameters and resulting properties by predicting the temperature history, and resulting residual stresses and metallurgical phase fractions for the DED process. A pre-processing framework was implemented in order to allow the modelling of complex geometries and laser trajectories while experiments were conducted to validate the fidelity of the model. Four separate cases were fabricated with varying processing parameters and geometries. In addition to in-situ temperature measurements, post-build residual stress and substrate distortion data was also collected. Furthermore, metallurgical analysis was performed for each case and compared with the simulated phase fractions. The accuracy of the distortion profile increased with increasing dwell time while the accuracy in predicting the metallurgical phase fractions and residual stresses demonstrated the opposite trend.
Graduate
2022-07-05

Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia
Robotics is destined to become the supporting technology that promotes the connection between the digital and the physical world. In an extremely competitive industrial environment, automated manufacturing is a key factor for any operation that seeks maximum efficiency, safety, and competitiveness. Despite its convenience, for certain functions, a robot is limited by its own axis system. The introduction of a coordinated system, with the external axis, allows flexibility and expansion of the robot's work zone in companies production lines.This thesis comprises the manipulation of external axes of a robotic cell applied to additive manufacturing. Offline programming methods are used in a virtual environment to assist the construction of an aircraft engine part using one of the direct energy deposition methods. The work carried out was focused on the production of a particular feature of an aircraft engine part, denominated here as Rim Part, which was initially tested on the RoboDK simulation software. During the tests, it was possible to conclude that the proposed impositions presented strong barriers to their production and for these reasons, it was necessary to change the approach, using macro programming, in C# language, to improve the coordinated movements between robots. With this method, simultaneously with the generated graphic interface, the production of the requested part was visualized, thus obtaining a very satisfactory result and without collisions between the two robots.
A robótica está destinada em tornar-se a tecnologia de suporte que promove a ligação entre o mundo digital e o físico. No meio industrial extremamente competitivo, a manufatura automatizada é um fator chave para qualquer operação que procure máxima eficiência, segurança e competitividade. Apesar da sua conveniência, para certas funções, um robô por si só é limitado pelo seu próprio sistema de eixos. A introdução de um sistema coordenado, com eixos externos, permite flexibilizar e expandir a zona de trabalho do robô nas linhas de produção das empresas. Esta tese compreende a aplicação de eixos externos num robô em manufatura aditiva e diferentes métodos de programação off-line num ambiente virtual, com o objetivo de auxiliar a construção de uma peça de um motor de avião utilizando um dos métodos de deposição direta de energia apresentados. O trabalho realizado foi focado na produção de uma feature em particular, designada por Rim Part, que inicialmente foi testado no software de simulação RoboDK. No decorrer dos ensaios, permitiu-se concluir que as imposições propostas apresentavam fortes barreiras à sua produção e por estes motivos, foi necessário mudar de abordagem recorrendo-se à programação de macros, em linguagem C#, para permitir os movimentos coordenados entre robôs. Com este método, juntamente com a interface gráfica gerada, foi possível a visualização da produção da parte requerida obtendo-se assim, um resultado bastante satisfatório e sem colisões entre os dois robôs.

Die generative Fertigung stellt eine Schlüsseltechnologie der Zukunft für weite Teile der Wirtschaft dar. Der Prozess des Plasma-Pulver-Auftragschweißens soll eine Lücke im bestehenden Portfolio an generativen Prozessen schließen. Zunächst wurde der klassische Beschichtungsprozess an die Erfordernisse der generativen Fertigung angepasst. Im Ergebnis konnten Bauteile, welche aus bis zu vier verschiedenen Materialen bestehen können, prozesssicher generiert werden. Die anschließende Betrachtung des Einflusses der Systemparameter auf das Bauteil ergab, dass die Haupteinflussgrößen auf die Bauteilgeometrie die Schweißstromstärke, die Schweißgeschwindigkeit, der Pulvermassestrom sowie die Plasmagasmenge sind. Die Bauteildichte sowie der Pulverausnutzungsgrad zeigen keine signifikanten Änderungen innerhalb des hier betrachteten Bereiches. Im Mittel konnte eine relative Bauteildichte von 98,7 % und ein Materialausnutzungsgrad von 77 % bestimmt werden. In Summe ist der Prozess durch eine stabile Auftragscharakteristik mit mindestens vergleichbaren Eigenschaften zu bestehenden Systemen zu bewerten und sehr gut als generativer Prozess, insbesondere für die Herstellung von mehrkomponentigen Bauteilen, geeignet.
Additive manufacturing is one of the key technologies of the future for large parts of the economy. The process of plasma powder deposition welding is intended to close a gap in the existing portfolio of generative processes. First, the classical cladding process was adapted to the requirements of additive manufacturing. As a result, components, which can consist of up to four different materials, could be reliably generated. The subsequent consideration of the influence of the system parameters on the component showed that the main influencing variables on the part geometry are the welding current, the welding speed, the powder flow rate and the plasma gas volume. The component density as well as the powder utilization rate show no significant changes within the range considered here. On average, a relative component density of 98.7 % and a material utilization rate of 77 % could be determined. In sum, the process can be characterized by a stable application characteristic with at least comparable properties to existing systems and is very well suitable as an additive manufacturing process, especially for the production of multi material components.