Browsing by Subject "electron beam additive manufacturing"

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Evaluations of Temperature Measurements By Near-Infrared Thermography in Powder-Based Electron-Beam Additive Manufacturing
(University of Texas at Austin, 2012-08-16) Price, Steven; Cooper, Ken; Chou, Kevin
Powder-based electron beam additive manufacturing (EBAM) has gained increased usage in different industries. Process monitoring such as temperatures may offer important information. However, temperature measurements in EBAM are challenging because of high temperature ranges, extreme gradients and fast transient response. In this study, temperature measurements during the EBAM process, in particular, around the electron beam scanning area, were attempted using a near-infrared thermal camera. The obtained temperature data demonstrated the feasibility of such a measuring technique. The thermal camera was able to capture the pre-heating, contour melting, and hatch melting events. Further, the achievable spatial resolution is around 12 µm when using a 350 mm lens.
Experimental Temperature Analysis of Powder-Based Electron Beam Additive Manufacturing
(University of Texas at Austin, 2013-08-16) Price, Steven; Lydon, James; Cooper, Ken; Chou, Kevin
A near infrared thermal imager has been employed for temperature measurements (build part surfaces) in the powder-based electron beam additive manufacturing (EBAM) process. A methodology has also been developed to analyze temperature distributions and history around the melting scan area. The temperature profiles along the beam scanning clearly show the moving source of heat phenomenon, with the peak temperature reaching over 2000 °C (for Ti6Al-4V) followed by extremely rapid cooling opposite to the beam scanning direction, except a slow-cooling portion corresponding to the liquidus-solidus range. The build surface temperatures and the melt pool sizes, in the localized electron beam scanning area, were studied at various configurations, e.g., different build heights, also with or without an overhang.
An Investigation into Melt Pool Effective Thermal Conductivity for Thermal Modeling of Powder-Bed Electron Beam Additive Manufacturing
(University of Texas at Austin, 2016) Shrestha, Subin; Cheng, Bo; Chou, Kevin
In this study, the effective thermal conductivity of a melt pool in the powder-bed electron beam additive manufacturing (EBAM) process was investigated using a numerical technique. Although a thermo-fluid model is preferred to predict the melt pool flow, computational cost is high. The alternative is to use an effective thermal conductivity that may capture the convection effect from the melt pool flow. Using finite volume method, first a thermo-fluid model was developed to simulate process temperatures in EBAM using Ti-6Al-4V powder and validated against experiment. Separately, a thermal simulation using an effective thermal conductivity for the liquid phase was conducted. The value of the effective thermal conductivity in the thermal simulation was adjusted so that the thermal responses approach those from the validated thermo-fluid simulations. The results show that the accuracy of thermal model depends on the process parameter. Maximum error of 35% was observed for beam diameter 0.55 mm.
Laser Heated Electron Beam Gun Optimization to Improve Additive Manufacturing
(University of Texas at Austin, 2018) Edinger, R.
Electron Beam Additive Manufacturing requires to improve electron gun characteristics to become a highly competitive manufacturing process. Our work targets the optimization of beam focusing to reduce the beam spot size, to improve the beam deflection system resulting in higher positioning accuracy, to refine thermal stability by minimizing heat induced drifting and to introduce a new powder delivery device which can be synchronized to beam parameters. Heisenberg's uncertainty principle states that if a position of a particle is precisely known, its momentum becomes less accurate and vice versa. Therefore, it will be required to conceive gun parameters optimizing the balance of opposing laws. Our goal is to deliver an open platform electron beam additive manufacturing machine which utilizes the results presented in this paper.
Melt Pool Geometry Simulations for Powder-Based Electron Beam Additive Manufacturing
(University of Texas at Austin, 2013-08-16) Cheng, Bo; Chou, Kevin
It is known that the melt pool geometry and dynamics strongly affect the build part properties in metal-based additive manufacturing (AM) processes. Thus, process temperature predictions may offer useful information of the melt pool evolution during the heating-cooling cycle. A transient thermal modeling for powder-based electron beam additive manufacturing (EBAM) process has been developed for process temperature simulations, considering temperature and porosity dependent thermal properties. In this study, the thermal model is applied to evaluate, for the case of Ti-6Al-4V in EBAM, the process parameter effects, such as the beam speed, on the temperature profile along the melt scan and the corresponding melt pool geometric characteristics such as the lengthdepth ratio and the cross-sectional area. The intent is to establish a process envelop for part quality control.
Microstructural Characterization and Modeling of Beam Speed Effects on Ti-6Al-4V by Electron Beam Additive Manufacturing
(University of Texas at Austin, 2014) Gong, X.; Lydon, J.; Cooper, K.; Chou, K.
In this study, the influence of the beam scanning speed to the microstructure of Ti-6Al4V parts processed by EBAM is investigated. EBAM parts were fabricated with 4 different scanning speeds, ranging from 214 mm/s to 689 mm/s, and the microstructures were studied. In addition, the volume fractions of different phases were obtained by thermal and phase transformation modeling. The microstructure is characterized by columnar structures of prior β grains along the build direction, and fine Widmanstätten (α+β) structure and α′ martensites are presented inside of the prior β. Both the prior β grain size and α-lath thickness decrease with the increase of the scanning speed. For the phase constitution, the volume fraction of α′ increases with the scanning speed while the volume fraction of α decreases due to the increase of cooling rate during solid phase transformation. The results from the analytical phase transformation model are consistent with the microstructure characterization from the experiment.
Numerical Thermal Analysis in Electron Beam Additive Manufacturing with Preheating Effects
(University of Texas at Austin, 2012-08-16) Shen, Ninggang; Chou, Kevin
In an early study, a thermal model has been developed, using finite element simulations, to study the temperature field and response in the electron beam additive manufacturing (EBAM) process, with an ability to simulate single pass scanning only. In this study, an investigation was focused on the initial thermal conditions, redesigned to analyze a critical substrate thickness, above which the preheating temperature penetration will not be affected. Extended studies are also conducted on more complex process configurations, such as multi-layer raster scanning, which are close to actual operations, for more accurate representations of the transient thermal phenomenon.
Residual Stress in Metal Parts Produced by Powder-Bed Additive Manufacturing Processes
(University of Texas at Austin, 2015) Wang, Xiaoqing; Chou, Kevin
In this study, residual stresses from the electron beam additive manufacturing (EBAM) and selective laser melting (SLM) processes, due to repeated thermal cycles, were investigated. Residual stresses play a crucial role in part performance, and thus, it is critical to evaluate the process-induced residual stresses in AM parts. Ti-6Al-4V and Inconel 718 parts produced by EBAM and SLM, respectively, were studied in residual stresses using the methodology established by Carlsson et al., a mechanical instrumented indentation technique, which is based on the experimental correlation between the indentation characteristic and the residual stress. The results show that the Ti-6Al-4V EBAM parts have a compressive residual stress in both Z-plane and X-plane, while the Inconel 718 SLM parts show a tensile stress and a compressive stress in the Z-plane and X-plane, respectively. Besides, the Ti-6Al-4V parts have lower absolute value of residual stress than the Inconel 718 parts. Moreover, the Vickers hardness values of the parts built using SLM and EBAM are comparable to the literature data.
Thermal Stresses Associated with Part Overhang Geometry in Electron Beam Additive Manufacturing: Process Parameter Effects
(University of Texas at Austin, 2014) Cheng, Bo; Chou, Kevin
For powder-bed electron beam additive manufacturing (EBAM), support structures are required when fabricating an overhang to prevent defects such as curling, which is due to the complex thermomechanical process in EBAM. In this study, finite element modeling is developed to simulate the thermomechanical process in EBAM in building overhang part. Thermomechanical characteristics such as thermal gradients and thermal stresses around the overhang build are evaluated and analyzed. The model is applied to evaluate process parameter effects on the severity of thermal stresses. The major results are summarized as follows. For a uniform set of process parameters, the overhang areas have a higher maximum temperature, a higher tensile stress, and a larger distortion than the areas above a solid substrate. A higher energy density input, e.g., a lower beam speed or a higher beam current may cause more severe curling at the overhang area.