Browsing by Subject "directed energy deposition"
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Item Beyond Laser-by-Laser Additive Manufacturing - Voxel-Wise Directed Energy Deposition(University of Texas at Austin, 2015) Nassar, A.R.; Reutzel, E.W.Conventional additive manufacturing is a layer-by-layer process, reliant on the sequential deposition of 2-1/2 D layers oriented along a build axis. During directed energy deposition a feedstock is directed into a continuous melt pool formed by a laser or electron beam. The ability to produce overhangs is limited due to the gravitational, surface tensions, and fluid-flow force acting on unsupported melt pools. Here, we present a novel, directed-energy-deposition technique where vertical and overhanging structures are formed by laser power modulation and the motion of a laser beam in three dimensional space along the build-up direction, rather than strictly in a single layer. We demonstrate that highly-overhanging Ti-6Al-4V structure, i.e. in which the overhang angle exceeds 45 degrees with respect to the x-y plane, can be deposited using the developed technique. High-speed imaging is used to gain insight into the physics of the process. The use of a pulsed or power-modulated beam is found to be critical to the formation of overhangs.Item Characterisation of Austenitic 316 LSi Stainless Steel Produced by Wire Arc Additive Manufacturing with Interlayer Cooling(University of Texas at Austin, 2019) Cunningham, C.R.; Wang, J.; Dhokia, V.; Shrokani, A.; Newman, S.T.Wire arc additive manufacturing (WAAM) expands the possibilities of cost effectively producing large-scale, complex metal objects at high deposition rates. Austenitic stainless steel is a commonly used material and has many applications in the marine and nuclear industry due to its high toughness and corrosion resistance. Processes parameters such as heat input and interpass temperature can greatly affect the materials properties, part functionality and the economics of WAAM production. However, the effect of these process parameters is not well understood for WAAM of 316LSi. In this research, the effects of the interpass temperature and heat input process parameters on WAAM of austenitic AISI 316LSi stainless steel are experimentally analysed and evaluated. It was found that the heat input and interpass temperature influences the cellular/dendritic morphology and the formation of macro-scale grains within the microstructure. Additionally, use of higher heat input, resulted in a 28.7% improvement in average Young’s modulus compared to lower heat input, although this remained lower than provided by wrought annealed material.Item Computer-Aided Process Planning for Wire Arc Directed Energy Deposition(University of Texas at Austin, 2019) Xiong, Yi; Dharmawan, Audelia Gumarus; Tang, YunlongWire arc directed energy deposition provides a rapid and cost-effective method for fabricating low-to-medium complexity and medium-to-large size metal parts. However, the complex nonequilibrium phase transformations, inherent to this process, make it a challenging task to produce consistent and high-quality parts, especially for parts with materials or geometries that have not been manufactured before. This study outlines a holistic and data-centric computer-aided process planning framework utilizing a knowledge base to assist engineers in selecting optimal process parameters that reduce dimensional deviations, and therefore to obtain near-net-shape parts using directed energy deposition only. The knowledge base has a data-knowledge-service architecture and is proposed to synthesize information from various sources, e.g., characterization tests. Based on these collected data, several knowledge representations, including database, metamodels, and planning rules, are constructed to support decision-making in the process planning. The proposed framework is demonstrated in the fabrication of components from industrial applications.Item Effect Of Inter-Layer Dwell Time on Residual Stresses in Directed Energy Deposition of High Strength Steel Alloy(University of Texas at Austin, 2023) Joy, Ranjit; Wu, Sung-Heng; Tariq, Usman; Mahmood, Muhammad Arif; Liou, FrankAdoption of metal additive manufacturing by various industries is being hindered by the presence of residual stresses and distortion in the deposited parts. Large thermal gradients during directed energy deposition often led to residual stresses in the final deposit. Parameter optimization is predominantly used for residual stress mitigation. However, the effect of process parameters is material specific. Current research aims to study the effect of inter-layer dwell time on residual stresses in directed energy deposition of high strength steel alloy. Specimens were deposited at three levels of inter-layer dwell time. Surface as well as bulk residual stresses were measured using X-ray diffraction. Both surface as well as bulk residual stresses were found to increase with an increase in the inter-layer dwell time.Item Effects of Inter-Layer Time Interval on Temperature Gradients in Direct Laser Deposited Ti-6Al-4V(University of Texas at Austin, 2016) Masoomi, Mohammad; Thompson, Scott M.; Shamsaei, Nima; Bian, LinkanParts fabricated via additive manufacturing (AM) methods are prone to experiencing high temperature gradients during manufacture resulting in internal residual stress formation. In the current study, a numerical model for predicting the temperature distribution and residual stress in Directed Energy Deposited (DED) Ti–6Al–4V parts is utilized for determining a relationship between local part temperature gradients with generated residual stress. Effects of time-interval between successive layer deposits, as well as layer deposition itself, on the temperature gradient vector for the first and each layer is investigated. The numerical model is validated using thermographic measurements of Ti-6Al-4V specimens fabricated via Laser Engineered Net Shaping® (LENS), a blown-powder/laser-based DED method. Results demonstrate the heterogeneity in the part’s spatiotemporal temperature field, and support the fact that as the part number, or single part size or geometry, vary, the resultant residual stress due to temperature gradients will be impacted. As the time inter-layer time interval increases from 0 to 10 second, the temperature gradient magnitude in vicinity of the melt pool will increase slightly.Item Estimating the Effects of Part Size on Direct Laser Deposition Parameter Selection via a Thermal Resistance Network Approach(University of Texas at Austin, 2016) Marshall, Garrett J.; Thompson, Scott M.; Daniewicz, Steve R.; Shamsaei, NimaA mathematical model for heat transfer during the Directed Energy Deposition (DED) process is proposed. The model employs the thermal resistance network analogy and is developed to aid one in predicting part size effects on its temperature distribution during manufacture, and in how to compensate such effects via suitable process parameter selection. The model predicts a pseudo steady-state temperature response in the melt pool. The temperature variation along the heat affected zone of a thin-walled part is estimated while assuming deposition is occurring far from the substrate. Predicted melt pool and bulk part temperatures are validated against Laser Engineering Net Shaping (LENSTM) experimental data obtained via a dual-wavelength pyrometer and in-chamber infrared camera, respectively. Results demonstrate that the model may be used to predict an average melt pool temperature. Bulk, calculated temperature distribution needs to be further investigated to find a more suitable heat transfer coefficient surrounding the part.Item Illumination and Image Processing for Real-Time Control of Directed Energy Deposition Additive Manufacturing(University of Texas at Austin, 2016) Seltzer, D.; Schiano, J.L.; Nassar, A.R.; Reutzel, E.W.This paper describes the optical setup and image processing required to estimate melt-pool width and build height for real-time control of melt-pool geometry in directed energy deposition additive manufacturing. To overcome optical interference from plasma emissions and laser interactions, the melt-zone is imaged using laser illumination. A single camera, fixed to the processing laser, views the laser interaction zone and provides images for estimating melt-zone width and build height. Using a bandpass filter and a single aspheric lens, the camera system provides sufficient magnification and depth of field to achieve a 1-mil (25.4 µm) resolution. Maintaining melt-zone geometry within desired tolerances requires an image acquisition and processing rate on the order of 100 frames per second. This bandwidth is achieved by a Camera Link camera and field-programmable gate array that implements algorithms for estimating melt-pool width and build height. The design and experimental verification of the camera, illumination, and processing systems are discussed.Item Impact of Directed Energy Deposition Parameters on Mechanical Distortion of Laser Deposited Ti-6Al-4V(University of Texas at Austin, 2016) Corbin, David J.; Nassar, Abdalla R.; Reutzel, Edward W.; Kistler, Nathan A.; Beese, Allison M.; Michaleris, PanThe effects of laser-based powder-fed directed energy deposition processing parameters on the distortion of deposited Ti-6Al-4V parts are assessed through in situ monitoring. Experiments were conducted wherein substrate thickness, deposition thickness, and initial substrate temperature were varied in order to investigate their effects on distortion. Correlations of process parameters to the mechanical characteristic were also developed, uncovering some of the driving mechanisms of the measured characteristic. This work highlights the impact of substrate preheating on distortion. Most notably, the effect of initial substrate temperature on distortion depended on the size of the substrate. On thin substrates, preheating reduced the total amount of distortion. However on thick substrates, preheating increased the amount of distortion. Techniques to mitigate the unwanted mechanical defect are discussed.Item MULTI-PHYSICS MODELING OF LOW-TEMPERATURE DIRECTED ENERGY DEPOSITION OF STAINLESS STEEL 316L(University of Texas at Austin, 2023) MN, Kishore; Qian, Dong; Li, WeiThe Directed energy deposition (DED) process is greatly influenced by the ambient temperature at on-site repair. In Northern Hemisphere locations, DED is particularly influenced by sub-freezing temperatures. However, its influence on the process is not yet studied. This critical gap is fulfilled in this research through a multi-physics computational fluid dynamics (CFD) modeling of the lowtemperature DED of the SS316L powders. The model is validated with test cases: −3°𝐶 for subfreezing and 20°𝐶 for room temperature cases using a cryogenic DED platform. The modeling involves powder spray, local melting, rapid cooling, solidification, evaporation, and fluid-gas interactions. The results show, at sub-freezing, the molten pool is ~63% bigger with the maximum temperature reduced by ~9.5%. The deposition saw an increase in width by ~8.6% and height by ~26% than the room temperature case. Overall, the versatile modeling-experimental platform helps study cryogenic DED cases for in-space additive manufacturing.Item Online Geometry Quality Management during Directed Energy Deposition using Laser Line Scaner(University of Texas at Austin, 2021) Yang, Liu; Binega, Eden; Cheng, Jack C.P.; Jeon, Ikgeun; Sohn, HoonAdditive manufacturing (AM) is a powerful and promising manufacturing technology due to its advantages of material saving, mass customization and small-quantity production of custom-designed products. However, current situation of lacking quality management in 3D printing process is the key barrier of adopting this advanced technology. Geometry inaccuracy of 3D printed components is one of the main quality problems for AM, especially when the final product requires high precision in its geometry. In this study, an online geometry quality management method for continuous monitoring during the direct energy deposition (DED) process was developed using a laser line scanner. Our proposed methodology comprises: (1) real-time track-by-track scanning of multi-layer single-track component, (2) online geometry extraction of multi-layer single-track component during printing process, and (3) online plotting and comparison of the as-designed and as-built models.Item OPTIMIZATION OF COMPUTATIONAL TIME FOR DIGITAL TWIN DATABASE IN DIRECTED ENERGY DEPOSITION FOR RESIDUAL STRESSES(University of Texas at Austin, 2023) Tariq, Usman; Joy, Ranjit; Wu, Sung-Heng; Arif Mahmood, Muhammad; Woodworth, Michael M.; Liou, FrankMetal Additive Manufacturing (MAM) has experienced rapid growth and demonstrated its cost-effectiveness in the production of high-quality products. However, MAM processes introduce significant thermal gradients that result in the formation of residual stresses and distortions in the final parts. Finite Element Analysis (FEA) is a valuable tool for predicting residual stresses, but it requires substantial computational power. This study aims to reduce computational time by incorporating a thermo-mechanical model specifically designed for the Directed Energy Deposition (DED) process using Ti6Al4V. This model predicts the thermal history and subsequent residual stresses in the deposited material. Various FEA methods, including “chunk”, layer, and conventional methods are examined, providing a comparative analysis of computational cost and numerical accuracy. These findings contribute towards the realization of a digital twin database, where the incorporation of efficient and accurate FEA models can optimize part quality and strength while reducing computational time.Item Particle-Melt Pool Interactions in Multi-Material Laser Based Directed Energy Deposition(University of Texas at Austin, 2021) Sellers, R.; Gould, B.; Wolff, S.Laser based metal directed energy deposition (DED) is an additive manufacturing process that is currently on the rise in the industry. However, there is still a knowledge gap in the understanding of fundamental interactions between particles and the melt pool in the DED process and how to change the parameters to alter microstructure. This work utilized synchronized in-situ thermal and X-ray imaging to understand the anomalous behavior of molybdenum powder binding onto a Ti-6Al-4V substrate as fundamental understanding for layer-by-layer processing. Using these visual techniques, particle velocity, mass, surface energy, kinetic energy, contact area, and temperature were observed and calculated. The correlation is shown and recorded to understand the wettability of particles and why some will bounce off of the substrate while others enter the melt pool. This work will allow for the manipulation of particle-melt pool interactions in DED which will help reproduce and build better parts more efficientlyItem Process Monitoring of Directed-Energy Deposition of Inconel-718 via Plume Imaging(University of Texas at Austin, 2015) Nassar, A.R.; Starr, Brandon; Reutzel, E.W.Laser-metal interactions typically results in vaporization and plume formation. These phenomena are complex and depend upon the details of the laser-vapor-melt interactions. As such, plume characteristics are sensitive to changes in process characteristics. Here, a spectroscopy-based imaging technique is presented for the monitoring of directed energy deposition of Inconel 718. Plume geometry is shown to be related to the processing parameters and geometry of single-bead deposits.Item Towards an Open-Source, Preprocessing Framework for Simulating Material Deposition for a Directed Energy Deposition Process(University of Texas at Austin, 2018) Dantin, Matthew J.; Furr, William M.; Priddy, Matthew W.This work focuses on the development of an open-source framework to simulate material deposition for arbitrary geometries with respect to desired process parameters during a directed energy deposition (DED) process. This framework allows the flexibility to define the element activation criteria used in conjunction with Abaqus. A Python script was developed to extract toolpath coordinates from G-code and implement an element activation sequence that is unique to a specific CAD drawing. This is important for simulating the additive manufacturing construction of complex geometries because the thermal history of the component is dependent on laser path, which has a significant effect on residual stresses and distortion. The results of varying the element activation criteria are compared with simulated temperature profiles.Item Towards directed energy deposition of metals using polymer-based supports: porosity of 316L stainless steel deposited on carbon-fiber-reinforced ABS(2022) Kurfess, Rebecca; Saleeby, Kyle; Feldhausen, Thomas; Fillingim, Blane; Hart, A. John; Hardt, DavidDirected energy deposition (DED) is increasingly valuable to many industries because of its high deposition rates relative to other metal additive manufacturing processes, but the design space of DED is limited. For instance, steep overhangs are difficult or impossible to manufacture. Polymer-based support structures could help address this challenge. The viability of DED on polymer composite substrates has begun to be explored, specifically with 316L stainless steel on carbon-fiber-reinforced ABS substrates. Monolithic metal components can be deposited on the polymer, but it was found that gas release during polymer degradation causes porosity due to gas entrapment in the metal. An interlayer cooling time was introduced to reduce polymer degradation and decrease the porosity due to gas entrapment, but this led to porosity from lack of fusion. The results of this work provide insight into process parameter selection and scan strategy development to enable the use of polymer support structures in blown-powder DED.Item Vibration-Actuated Powder Dispensing for Directed Energy Deposition Systems(University of Texas at Austin, 2021) Greeley, Andrew; Cormier, DenisUsers of powder-fed directed energy deposition system often face several challenges associated with conventional powder delivery sub-systems. In addition to the high cost of wasted powder, it can be difficult to plan for the amount of material being deposited when some of the dispensed powder is not captured in the melt pool. This work studies the effectiveness of a vibration-actuated powder dispensing system using a nozzle with a small capillary opening. The opening is sized so that particle contact forces arrest powder flow when the vibration actuator is turned off. The relative effects of vibration frequency, vibration acceleration, nozzle size and nozzle inclination are compared with the goal of having the output mass flow rate monotonically change with one of these parameters. For the materials and parameters explored in this study, nozzle inclination is found to have the largest effect on mass flow rate output and has the desired monotonically changing relationship.