Thermomechanical Investigation of Overhang Fabrications in Electron Beam Additive Manufacturing

2014 ◽  
Author(s):  
Bo Cheng ◽  
Ping Lu ◽  
Kevin Chou
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
Residual Stresses ◽  
Heat Dissipation ◽  
Element Model ◽  
Full Density ◽  
Support Structures ◽  
Powder Bed ◽  
Thermomechanical Process ◽  
Root Cause

Electron beam additive manufacturing (EBAM) is one of powder-bed-fusion additive manufacturing processes that are capable of making full density metallic components. EBAM has a great potential in various high-value, small-batch productions in biomedical and aerospace industries. In EBAM, because a build part is immersed in the powder bed, ideally the process would not require support structures for overhang geometry. However, in practice, support structures are indeed needed for an overhang; without it, the overhang area will have defects such as warping, which is due to the complex thermomechanical process in EBAM. In this study, a thermomechanical finite element model has been developed to simulate temperature and stress fields when building a simple overhang in order to examine the root cause of overhang warping. It is found that the poor thermal conductivity of Ti-6Al-4V powder results in higher temperatures, also slower heat dissipation, in an overhang area, in EBAM builds. The retained higher temperatures in the area above the powder substrate result in higher residual stresses in an overhang area, and lower powder porosity may reduce the residual stresses associated with building an overhang.

Thermofluid Properties of Ti-6Al-4V Melt Pool in Powder-Bed Electron Beam Additive Manufacturing

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
M Shafiqur Rahman ◽  
Paul J. Schilling ◽  
Paul D. Herrington ◽  
Uttam K. Chakravarty
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
Heat Source ◽  
Thermal Behavior ◽  
Source Parameters ◽  
Three Dimensional ◽  
Full Density ◽  
Layer By Layer ◽  
Powder Bed ◽  
Melt Pool

Electron beam additive manufacturing (EBAM) is a powder-bed fusion additive manufacturing (AM) technology that can make full density metallic components using a layer-by-layer fabrication method. To build each layer, the EBAM process includes powder spreading, preheating, melting, and solidification. The quality of the build part, process reliability, and energy efficiency depends typically on the thermal behavior, material properties, and heat source parameters involved in the EBAM process. Therefore, characterizing those properties and understanding the correlations among the process parameters are essential to evaluate the performance of the EBAM process. In this study, a three-dimensional computational fluid dynamics (CFD) model with Ti-6Al-4V powder was developed incorporating the temperature-dependent thermal properties and a moving conical volumetric heat source with Gaussian distribution to conduct the simulations of the EBAM process. The melt pool dynamics and its thermal behavior were investigated numerically, and results for temperature profile, melt pool geometry, cooling rate and variation in density, thermal conductivity, specific heat capacity, and enthalpy were obtained for several sets of electron beam specifications. Validation of the model was performed by comparing the simulation results with the experimental results for the size of the melt pool.

Thermal Analysis of Electron Beam Additive Manufacturing Using Ti-6Al-4V Powder-Bed

2017 ◽  
Author(s):  
M. Shafiqur Rahman ◽  
Paul J. Schilling ◽  
Paul D. Herrington ◽  
Uttam K. Chakravarty
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
Three Dimensional ◽  
Vital Role ◽  
Full Density ◽  
Rate Variation ◽  
Layer By Layer ◽  
Powder Bed ◽  
Part Quality ◽  
Melt Pool

Electron Beam Additive Manufacturing (EBAM) is one of the emerging additive manufacturing (AM) technologies that is uniquely capable of making full density metallic components using layer-by-layer fabrication method. To build each layer, the process includes powder spreading, pre-heating, melting, and solidification. The thermal and material properties involved in the EBAM process play a vital role to determine the part quality, reliability, and energy efficiency. Therefore, characterizing the properties and understanding the correlations among the process parameters are incumbent to evaluate the performance of the EBAM process. In this study, a three dimensional computational fluid dynamics (CFD) model with Ti-6Al-4V powder has been developed incorporating the temperature-dependent thermal properties and a moving conical volumetric heat source with Gaussian distribution to conduct the simulations of the EBAM process. The melt-pool dynamics and its thermal behavior have been investigated numerically using a CFD solver and results for temperature profile, cooling rate, variation in density, thermal conductivity, specific heat capacity, and enthalpy have been obtained for a particular set of electron beam specifications.

scholarly journals Thermo-Mechanical Modeling of Wire-Fed Electron Beam Additive Manufacturing

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 911
Author(s):  
Fatih Sikan ◽  
Priti Wanjara ◽  
Javad Gholipour ◽  
Amit Kumar ◽  
Mathieu Brochu
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
Residual Stresses ◽  
Single Layer ◽  
Grain Morphology ◽  
Element Model ◽  
Primary Objective ◽  
Average Error ◽  
Thin Wall ◽  
Compressive Stresses

The primary objective of this research was to develop a finite element model specifically designed for electron beam additive manufacturing (EBAM) of Ti-6Al-4V to understand metallurgical and mechanical aspects of the process. Multiple single-layer and 10-layer build Ti-6Al-4V samples were fabricated to validate the simulation results and ensure the reliability of the developed model. Thin wall plates of 3 mm thickness were used as substrates. Thermocouple measurements were recorded to validate the simulated thermal cycles. Predicted and measured temperatures, residual stresses, and distortion profiles showed that the model is quite reliable. The thermal predictions of the model, when validated experimentally, gave a low average error of 3.7%. The model proved to be extremely successful for predicting the cooling rates, grain morphology, and the microstructure. The maximum deviations observed in the mechanical predictions of the model were as low as 100 MPa in residual stresses and 0.05 mm in distortion. Tensile residual stresses were observed in the deposit and the heat-affected zone, while compressive stresses were observed in the core of the substrate. The highest tensile residual stress observed in the deposit was approximately 1.0 σys (yield strength). The highest distortion on the substrate was approximately 0.2 mm.

Overhang Support Structure Design for Electron Beam Additive Manufacturing

2017 ◽  
Author(s):  
Bo Cheng ◽  
Y. Kevin Chou
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
Design Process ◽  
Heat Dissipation ◽  
Design Method ◽  
Solid Substrate ◽  
Structure Design ◽  
Process Time ◽  
Support Structure ◽  
Powder Bed

Overhang structures are commonly found in Powder-bed metal additive manufacturing (AM) such as electron beam additive manufacturing (EBAM) process. The EBAM is assumed to build overhang structure without support features since powder bed could provide support. However, heat dissipation difference by sintered powder and solid substrate for overhang feature actually causes severe part distortion and requires support structure. Current support generation methods usually used certain types of structure to cover the overhang space. They may overestimate the support volume or put a large amount of supports, which could not be necessary and increase the post process time. Thus, the object of this task is to enhance the performance and efficient usage of the EBAM technology through effective support structure designs. In this study, a combined heat support and support anchor design method has been proposed. Numerical model has been used to evaluate stress and deformation during the design process. The detailed design process has been presented for a typical overhang and the simulation results have indicated that overhang deformation can be greatly reduced using this new method.

Simulations of Thermo-Mechanical Characteristics in Electron Beam Additive Manufacturing

2012 ◽  
Author(s):  
Ninggang Shen ◽  
Kevin Chou
Keyword(s):  
Heat Transfer ◽  
Electron Beam ◽  
Additive Manufacturing ◽  
Residual Stresses ◽  
High Energy ◽  
Heat Transfer Analysis ◽  
Full Density ◽  
Metal Powders ◽  
Metallic Parts ◽  
Scan Pattern

In the direct digital metal manufacturing, Electron Beam Additive Manufacturing (EBAM) has been used to fabricate sophisticated metallic parts, in a layer by layer fashion, by sintering and/or melting metal powders. In principle, EBAM utilizes a high-energy electron beam to melt and fuse metal powders to build solid parts with various materials, such as Ti-6Al-4V which is very difficult to fabricate using conventional processes. EBAM is one of a few Additive Manufacturing (AM) technologies capable of making full-density metallic parts and has drastically extended AM applications. The heat transfer analysis has been conducted in a simple case of a single-scan path with the effect of powder porosity investigated. In the actual EBAM process, the scan pattern is typically alternate raster. In this study, a coupled thermo-mechanical finite element model was developed to simulate the transient heat transfer, part residual stresses of alternate raster during the EBAM process subject to a moving heat source with a Gaussian volumetric distribution. The developed model was first examined against literature data. The coupled mechanical simulation is able to capture the evolution of the part residual stresses in EBAM.

Deformation Evaluation of Part Overhang Configurations in Electron Beam Additive Manufacturing

2015 ◽  
Author(s):  
Bo Cheng ◽  
Kevin Chou
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
Beam Current ◽  
Solid Substrate ◽  
Industrial Applications ◽  
Deformation Condition ◽  
Fe Model ◽  
Porosity Level ◽  
Powder Bed ◽  
Thermomechanical Process

Powder-bed electron beam additive manufacturing (EBAM) has emerged as a cost-effective process for many industrial applications. Intuitively, EBAM would not require support structures for overhang geometry because the powder bed would self-support the overhang weight. However, without a proper support structure, overhang warping actually occurs in practices. In this study, a two dimensional (2D) finite element (FE) model was developed to study the thermomechanical process of EBAM. The model was applied to evaluate (1) the process parameter effect, (2) the overhang and support configuration effect, and (3) the powder porosity effect on overhang deformations. The major results are summarized as follows. (1) Increasing the beam speed and diameter will result in less deformation in an overhang area, while increasing the beam current will worsen the deformation condition. (2) A smaller tilt angle will cause a larger overhang deformation. (3) A support column, even placed away from the solid substrate side, will minimize overhang deformations. (4) An anchor-free solid piece beneath the overhang can reduce the deformation with an appropriate gap. (5) A lower powder porosity level may alleviate overhang deformations.

scholarly journals A Simplified Methodology for Estimating Residual Stresses in Powder-Bed Electron Beam Additive Manufacturing

2018 ◽  
Vol 59 (3) ◽  
pp. 420-424
Author(s):  
Satoshi Tadano ◽  
Shigetaka Okano ◽  
Takehisa Hino ◽  
Haruki Ohnishi ◽  
Masahito Mochizuki ◽  
...  
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
Residual Stresses ◽  
Powder Bed

scholarly journals Comparison of Phase Characteristics and Residual Stresses in Ti-6Al-4V Alloy Manufactured by Laser Powder Bed Fusion (L-PBF) and Electron Beam Powder Bed Fusion (EB-PBF) Techniques

Crystals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 796
Author(s):  
Aya Takase ◽  
Takuya Ishimoto ◽  
Naotaka Morita ◽  
Naoko Ikeo ◽  
Takayoshi Nakano
Keyword(s):  
Electron Beam ◽  
Residual Stresses ◽  
Cooling Rate ◽  
Process Parameters ◽  
Phase Evolution ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Solidification Temperature ◽  
Powder Bed ◽  
Β Phase

Ti-6Al-4V alloy fabricated by laser powder bed fusion (L-PBF) and electron beam powder bed fusion (EB-PBF) techniques have been studied for applications ranging from medicine to aviation. The fabrication technique is often selected based on the part size and fabrication speed, while less attention is paid to the differences in the physicochemical properties. Especially, the relationship between the evolution of α, α’, and β phases in as-grown parts and the fabrication techniques is unclear. This work systematically and quantitatively investigates how L-PBF and EB-PBF and their process parameters affect the phase evolution of Ti-6Al-4V and residual stresses in the final parts. This is the first report demonstrating the correlations among measured parameters, indicating the lattice strain reduces, and c/a increases, shifting from an α’ to α+β or α structure as the crystallite size of the α or α’ phase increases. The experimental results combined with heat-transfer simulation indicate the cooling rate near the β transus temperature dictates the resulting phase characteristics, whereas the residual stress depends on the cooling rate immediately below the solidification temperature. This study provides new insights into the previously unknown differences in the α, α’, and β phase evolution between L-PBF and EB-PBF and their process parameters.

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