Effect of Thermal Deformation on Part Errors in Metal Powder Based Additive Manufacturing Processes

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Ratnadeep Paul ◽  
Sam Anand ◽  
Frank Gerner
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
Thermal Deformation ◽  
Thermal Stresses ◽  
Geometric Model ◽  
Virtual Manufacturing ◽  
Deformation Model ◽  
Fe Model ◽  
Slice Thickness ◽  
Part Orientation

In metal additive manufacturing (AM) processes, parts are manufactured in layers by sintering or melting metal or metal alloy powder under the effect of a powerful laser or an electron beam. As the laser/electron beam scans the powder bed, it melts the powder in successive tracks which overlap each other. This overlap, called the hatch overlap, results in a continuous cycle of rapid melting and resolidification of the metal. The melting of the metal from powder to liquid and subsequent solidification causes anisotropic shrinkage in the layers. The thermal strains caused by the thermal gradients existing between the different layers and between the layers and the substrate leads to considerable thermal stresses in the part. As a result, stress gradients develop in the different directions of the part which lead to distortion and warpage in AM parts. The deformations due to shrinkage and thermal stresses have a significant effect on the dimensional inaccuracies of the final part. A three-dimensional thermomechanical finite element (FE) model has been developed in this paper which calculates the thermal deformation in AM parts based on slice thickness, part orientation, scanning speed, and material properties. The FE model has been validated and benchmarked with results already available in literature. The thermal deformation model is then superimposed with a geometric virtual manufacturing model of the AM process to calculate the form and runout errors in AM parts. Finally, the errors in the critical features of the AM parts calculated using the combined thermal deformation and geometric model are correlated with part orientation and slice thickness.

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 Riddance jamming of pipeline shut-off valves

2021 ◽  
Vol 29 (3) ◽  
pp. 83-97
Author(s):  
Alexander A. Bazarov ◽  
Nataliya V. Bondareva ◽  
Ashot A. Navardyan
Keyword(s):  
Ambient Temperature ◽  
Thermal Deformation ◽  
Thermal Stresses ◽  
The Body ◽  
Deformation Model ◽  
Horizontal Line ◽  
Average Height ◽  
Temperature Decrease ◽  
Structural Elements ◽  
Valve Body

The paper conciders the problems of modeling the processes of thermal deformation of valves with an ambient temperature decrease. Some type of wedge valves are exposed to jamming. Heating the valve body is used to eliminate jamming. This problem is common for rigid wedge valves but the reasons not fully explained. Sometimes the valve stem is destroyed due to the significant power of the gate valve electric drives. The aim of the study is to determine the nature of the stress distribution between the structural elements of the valve, which are the cause of jamming with an ambient temperature decrease, and to search for the parameters of the heating process that ensure minimum energy consumption and time. To study the thermal processes in the valve body, a numerical model describing the heat transfer in the structural elements and the fluid is developed. The thermal model is combined with the elastic deformation model. That allows to make compatible calculations without introducing additional errors. The thermal deformations appear in the cooling process and give rise to disproportionate changes in valve dimensions and thermal stresses. Thermal stresses are the cause of jamming. Modeling of the processes of thermal deformation with a decrease in temperature showed that pressure forces of different signs arise in the middle plane of the wedge. At the average height of the horizontal line, there is a compacting pressure and at the lower and upper points there is a stretching pressure. To eliminate the compacting forces local heating was performed in several areas of the body. It was found that the most effective option is to heat the lower hemispherical surface of the body. Heating for thirty minutes reduces the thermal stresses in the wedge and compressive forces to minimum values. For this reason, jamming of the valve is eliminated. For heating the body, a hemispherical induction heater with a magnetic core is provided. The proposed design allows the use of industrial frequency voltage without a step-down transformer and reactive power compensation.

scholarly journals A Voxel-Based Watermarking Scheme for Additive Manufacturing

2021 ◽  
Vol 11 (19) ◽  
pp. 9177
Author(s):  
Shyh-Kuang Ueng ◽  
Ya-Fang Hsieh ◽  
Yu-Chia Kao
Keyword(s):  
Additive Manufacturing ◽  
Geometric Model ◽  
Region Of Interest ◽  
Virtual Manufacturing ◽  
Test Results ◽  
Volumetric Models ◽  
Complex Models ◽  
G Code ◽  
Watermarking Scheme ◽  
Am Processes

Digital and analog contents, generated in additive manufacturing (AM) processes, may be illegally modified, distributed, and reproduced. In this article, we propose a watermarking scheme to enhance the security of AM. Compared with conventional watermarking methods, our algorithm possesses the following advantages. First, it protects geometric models and printed parts as well as G-code programs. Secondly, it embeds watermarks into both polygonal and volumetric models. Thirdly, our method is capable of creating watermarks inside the interiors and on the surfaces of complex models. Fourth, the watermarks may appear in various forms, including character strings, cavities, embossed bumps, and engraved textures. The proposed watermarking method is composed of the following steps. At first, the input geometric model is converted into a distance field. Then, the watermark is inserted into a region of interest by using self-organizing mapping. Finally, the watermarked model is converted into a G-code program by using a specialized slicer. Several robust methods are also developed to authenticate digital models, G-code programs, and physical parts. These methods perform virtual manufacturing, volume rendering, and image processing to extract watermarks from these contents at first. Then, they employ similarity evaluation and visual comparison to verify the extracted signatures. Some experiments had been conducted to validify the proposed watermarking method. The test results, analysis, discussion, and comparisons are also presented in this article.

A Procedure for Determining the Operating Modes of Electron Beam Wire Feed Layer-Wise Deposition for Additive Manufacturing

Vestnik MEI ◽  
2017 ◽  
pp. 8-14 ◽  
Author(s):  
Aleksandr V. Gudenko ◽  
◽  
Viktor К. Dragunov ◽  
Andrey Р. Sliva ◽  
◽  
...  
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
Operating Modes ◽  
Wire Feed

scholarly journals Contactless temperature measurement in wire-based electron beam additive manufacturing Ti-6Al-4V

2021 ◽  
Author(s):  
F. Pixner ◽  
R. Buzolin ◽  
S. Schönfelder ◽  
D. Theuermann ◽  
F. Warchomicka ◽  
...  
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
Thermal Imaging ◽  
Temperature Profiles ◽  
Layer By Layer ◽  
Thermal Cycles ◽  
Cooling Rates ◽  
Geometric Boundary ◽  
Microstructural Characterisation ◽  
Local Misorientation

AbstractThe complex thermal cycles and temperature distributions observed in additive manufacturing (AM) are of particular interest as these define the microstructure and the associated properties of the part being built. Due to the intrinsic, layer-by-layer material stacking performed, contact methods to measure temperature are not suitable, and contactless methods need to be considered. Contactless infrared irradiation techniques were applied by carrying out thermal imaging and point measurement methods using pyrometers to determine the spatial and temporal temperature distribution in wire-based electron beam AM. Due to the vacuum, additional challenges such as element evaporation must be overcome and additional shielding measures were taken to avoid interference with the contactless techniques. The emissivities were calibrated by thermocouple readings and geometric boundary conditions. Thermal cycles and temperature profiles were recorded during deposition; the temperature gradients are described and the associated temperature transients are derived. In the temperature range of the α+β field, the cooling rates fall within the range of 180 to 350 °C/s, and the microstructural characterisation indicates an associated expected transformation of β→α'+α with corresponding cooling rates. Fine acicular α and α’ formed and local misorientation was observed within α as a result of the temperature gradient and the formation of the α’.

scholarly journals Directionally-Dependent Mechanical Properties of Ti6Al4V Manufactured by Electron Beam Melting (EBM) and Selective Laser Melting (SLM)

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3603
Author(s):  
Tim Pasang ◽  
Benny Tavlovich ◽  
Omry Yannay ◽  
Ben Jakson ◽  
Mike Fry ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Surface Roughness ◽  
Tensile Strength ◽  
Electron Beam ◽  
Additive Manufacturing ◽  
Selective Laser Melting ◽  
Electron Beam Melting ◽  
Rolling Direction ◽  
Laser Melting ◽  
Plate Rolling

An investigation of mechanical properties of Ti6Al4V produced by additive manufacturing (AM) in the as-printed condition have been conducted and compared with wrought alloys. The AM samples were built by Selective Laser Melting (SLM) and Electron Beam Melting (EBM) in 0°, 45° and 90°—relative to horizontal direction. Similarly, the wrought samples were also cut and tested in the same directions relative to the plate rolling direction. The microstructures of the samples were significantly different on all samples. α′ martensite was observed on the SLM, acicular α on EBM and combination of both on the wrought alloy. EBM samples had higher surface roughness (Ra) compared with both SLM and wrought alloy. SLM samples were comparatively harder than wrought alloy and EBM. Tensile strength of the wrought alloy was higher in all directions except for 45°, where SLM samples showed higher strength than both EBM and wrought alloy on that direction. The ductility of the wrought alloy was consistently higher than both SLM and EBM indicated by clear necking feature on the wrought alloy samples. Dimples were observed on all fracture surfaces.

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