Browsing by Subject "electron beam"

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Controlling Melt Pool Dimensions Over a Wide Range of Material Deposition Rates in Electron Beam Additive Manufacturing
(University of Texas at Austin, 2010) Soylemez, Emrecan; Beuth, Jack L.
Electron beam-based additive manufacturing processes are being seriously considered for manufacturing and repair applications in the aerospace industry. To be successful, these processes must work over a wide range of material deposition rates to combine affordability (requiring high deposition rates) with the ability to precisely deposit fine geometries (requiring low deposition rates). Melt pool size and shape are key characteristics to control in these processes. Control of melt pool dimensions will greatly increase the ability to successfully build shapes, and may play an important role in controlling solidification microstructure. In this paper, we present an analytically-guided approach for maintaining melt pool cross sectional area and thermal finite element simulation results are presented over a wide power range (1-5kW) to evaluate the approach. Single bead finite element simulations include the effects of temperature-dependent properties, latent heat, material addition and the distribution of power by a rapidly moving beam. Experiments were carried out on electron beam deposition equipment at NASA Langley Research Center and results show the same trends as those seen in the models. Ultimately, a map of curves of constant melt pool cross sectional areas and length-to-depth ratios is presented, covering power and velocity ranges over roughly a factor of 5.
Grain Refinement of Freeform Fabricated Ti-6Al-4V Alloy Using Beam/Arc Modulation
(University of Texas at Austin, 2012) Mitzner, Scott; Liu, Stephen; Domack, Marcia; Hafley, Robert
Grain refinement can significantly improve the mechanical properties of freeform-fabricated Ti6Al-4V alloy, promoting increased strength and enhanced isotropy compared with coarser grained material. Large β-grains can lead to a segregated microstructure, in regard to both αphase morphology and α-lath orientation. Beam modulation, which has been used in conventional fusion welding to promote grain refinement, is explored in this study for use in additive manufacturing processes including electron beam freeform fabrication (EBF3) and gas-tungsten arc (GTA) deposition to alter solidification behavior and produce a refined microstructure. The dynamic molten pool size, induced by beam modulation causes rapid heat flow variance and results in a more competitive grain growth environment, reducing grain size. Consequently, improved isotropy and strength can be achieved with relatively small adjustments to deposition parameters.
Transient Physical Effects in Electron Beam Sintering
(2006-09-14) Sigl, M.; Lutzmann, S.; Zaeh, M.F.
The extensive use of the electron beam in manufacturing processes like welding or perforating revealed the high potentials for also using it for solid freeform fabrication. First approaches like feeding wire into a melt pool have successfully shown the technical feasibility. Among other features, the electron beam exhibits high scanning speed, high power output, and beam density. While in laser-based machines the fabrication is working in a stable way, transient physical effects in the electron beam process can be observed, which still restrict process stability. For instance, a high power input of the electron beam can result in sudden scattering of the metal powder. The authors have developed an electron beam freeform fabrication system and examined the above mentioned effects. Thus, the paper provides methods in order to identify, isolate and avoid these effects, and to finally realize a reproducible process.
Variability in the Geometric Accuracy of Additively Manufactured Test Parts
(University of Texas at Austin, 2010) Cooke, A.L.; Soons, J.A.
This paper describes the results of a study on the variability in the geometric accuracy of a metal test part manufactured by several service providers using either an electron beam or laser beam powder bed thermal fusion process. The part was a circle-diamond-square test part with an inverted cone that is used to evaluate the performance of five-axis milling machines. The study was conducted to aid development of standardized parameters and test methods to specify and evaluate the performance of additive manufacturing systems. Without standards for performance characterization, it is difficult to match system capabilities with part requirements and ensure consistent and predictable part quality across systems, operators, and manufacturing facilities.