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.

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.

Hybrid Modeling of Melt Pool Geometry in Additive Manufacturing Using Neural Networks

2021 ◽  
Author(s):  
Kevontrez Jones ◽  
Zhuo Yang ◽  
Ho Yeung ◽  
Paul Witherell ◽  
Yan Lu
Keyword(s):  
Neural Networks ◽  
Finite Element ◽  
Additive Manufacturing ◽  
Real Time ◽  
Hybrid Model ◽  
Computational Models ◽  
Single Layer ◽  
Element Model ◽  
Additive Process ◽  
Melt Pool

Abstract Laser powder-bed fusion is an additive manufacturing (AM) process that offers exciting advantages for the fabrication of metallic parts compared to traditional techniques, such as the ability to create complex geometries with less material waste. However, the intricacy of the additive process and extreme cyclic heating and cooling leads to material defects and variations in mechanical properties; this often results in unpredictable and even inferior performance of additively manufactured materials. Key indicators for the potential performance of a fabricated part are the geometry and temperature of the melt pool during the building process, due to its impact upon the underlining microstructure. Computational models, such as those based on the finite element method, of the AM process can be used to elucidate and predict the effects of various process parameters on the melt pool, according to physical principles. However, these physics-based models tend to be too computationally expensive for real-time process control. Hence, in this work, a hybrid model utilizing neural networks is proposed and demonstrated to be an accurate and efficient alternative for predicting melt pool geometries in AM, which provides a unified description of the melting conditions. The results of both a physics-based finite element model and the hybrid model are compared to real-time experimental measurements of the melt pool during single-layer AM builds using various scanning strategies.

Effect of post-processing on microstructure and mechanical properties of Alloy 718 fabricated using powder bed fusion additive manufacturing processes

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Sareh Götelid ◽  
Taoran Ma ◽  
Christophe Lyphout ◽  
Jesper Vang ◽  
Emil Stålnacke ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Additive Manufacturing ◽  
Residual Stresses ◽  
Design Methodology ◽  
Hot Isostatic Pressing ◽  
Powder Bed Fusion ◽  
Content Type ◽  
Powder Bed ◽  
Nickel Based Superalloy ◽  
Compressive Stresses

Purpose This study aims to investigate additive manufacturing of nickel-based superalloy IN718 made by powder bed fusion processes: powder bed fusion laser beam (PBF-LB) and powder bed fusion electron beam (PBF-EB). Design/methodology/approach This work has focused on the influence of building methods and post-fabrication processes on the final part properties, including microstructure, surface quality, residual stresses and mechanical properties. Findings PBF-LB produced a much smoother surface. Blasting and shot peening (SP) reduced the roughness even more but did not affect the PBF-EB surface finish as much. As-printed PBF-EB parts have low residual stresses in all directions, whereas it was much higher for PBF-LB. However, heat treatment removed the stresses and SP created compressive stresses for samples from both PBF processes. The standard Arcam process parameter for PBF-EB for IN718 is not fully optimized, which leads to porosity and inferior mechanical properties. However, impact toughness after hot isostatic pressing was surprisingly high. Originality/value The two processes gave different results and also responses to post-treatments, which could be of advantage or disadvantage for different applications. Suggestions for improving the properties of parts produced by each method are presented.

scholarly journals Residual Stresses Control in Additive Manufacturing

2021 ◽  
Vol 5 (4) ◽  
pp. 138
Author(s):  
Xufei Lu ◽  
Miguel Cervera ◽  
Michele Chiumenti ◽  
Xin Lin
Keyword(s):  
Additive Manufacturing ◽  
Residual Stresses ◽  
Thermal Deformation ◽  
Element Model ◽  
Thermal Gradients ◽  
Part Geometry ◽  
The Core ◽  
Optimal Processing ◽  
Scan Pattern ◽  
Metal Additive

Residual stresses are one of the primary causes for the failure of parts or systems in metal additive manufacturing (AM), since they easily induce crack propagation and structural distortion. Although the formation of residual stresses has been extensively studied, the core factors steering their development in AM have not been completely uncovered. To date, several strategies based on reducing the thermal gradients have been developed to mitigate the manifestation of residual stresses in AM; however, how to choose the optimal processing plan is still unclear for AM designers. In this regard, the concept of the yield temperature, related to the thermal deformation and the mechanical constraint, plays a crucial role for controlling the residual stresses, but it has not been duly investigated, and the corresponding approach to control stresses is also yet lacking. To undertake such study, a three-bar model is firstly used to illustrate the formation mechanism of the residual stress and its key causes. Next, an experimentally calibrated thermomechanical finite element model is used to analyze the sensitivity of the residual stresses to the scan pattern, preheating, energy density, and the part geometry and size, as well as the substrate constraints. Based on the numerical results obtained from this analysis, recommendations on how to minimize the residual stresses during the AM process are provided.

scholarly journals Understanding the edge crack phenomenon in ceramic laminates

2015 ◽  
Author(s):  
O. Ševeek, ◽  
M. Kotoul ◽  
D. Leguillon ◽  
E. Martin ◽  
R. Bermejo
Keyword(s):  
Residual Stresses ◽  
Edge Crack ◽  
Energy Criterion ◽  
Element Model ◽  
Ceramic Materials ◽  
Brittle Behavior ◽  
Compressive Stresses ◽  
Out Of Plane ◽  
Edge Cracks ◽  
Edge Cracking

Layered ceramic materials (also referred to as “ceramic laminates”) are becoming one of the most promising areas of materials technology aiming to improve the brittle behavior of bulk ceramics. The utilization of tailored compressive residual stresses acting as physical barriers to crack propagation has already succeeded in many ceramic systems. Relatively thick compressive layers located below the surface have proven very effective to enhance the fracture resistance and provide a minimum strength for the material. However, internal compressive stresses result in out-of plane stresses at the free surfaces, what can cause cracking of the compressive layer, forming the so-called edge cracks. Experimental observations have shown that edge cracking may be associated with the magnitude of the compressive stresses and with the thickness of the compressive layer. However, an understanding of the parameters related to the onset and extension of such edge cracks in the compressive layers is still lacking. In this work, a 2D parametric finite element model has been developed to predict the onset and propagation of an edge crack in ceramic laminates using a coupled stress-energy criterion. This approach states that a crack is originated when both stress and energy criteria are fulfilled simultaneously. Several designs with different residual stresses and a given thickness in the compressive layers have been computed. The results predict the existence of a lower bound, below no edge crack will be observed, and an upper bound, beyond which the onset of an edge crack would lead to the complete fracture of the layer.

scholarly journals Effects of Thermal Undercooling and Thermal Cycles on the Grain and Microstructure Evolution of TC17 Titanium Alloy Repaired by Wire Arc Additive Manufacturing

2021 ◽  
Author(s):  
Yimin Zhuo ◽  
Chunli Yang ◽  
Chenglei Fan ◽  
Sanbao Lin
Keyword(s):  
Titanium Alloy ◽  
Additive Manufacturing ◽  
High Efficiency ◽  
Low Cost ◽  
Single Layer ◽  
Element Model ◽  
Maximum Effect ◽  
Thermal Cycles ◽  
Layer Deposition ◽  
Wire Arc Additive Manufacturing

Abstract Wire arc additive manufacturing (WAAM) can be used to repair blades or blisk made of titanium alloy with the advantage of high efficiency and low-cost. In this work, the finite element model of repairing the blade based on the arc heat source was established to investigate it. Results showed that the maximum effect of thermal undercooling appears when the peak current transforms to the base current (1Hz or 5Hz), which will promote the grains refinement with the combination of sufficient constitutional supercooling. Compared to the single-layer deposition, the microstructure in the near-heat affected zone (near-HAZ) of multi-layer deposition changes from the metastable β phases to the extremely fine α phases, which was caused by the repeated thermal cycles.

scholarly journals Optimization of Process Parameters to Improve the Effective Area of Deposition in GMAW-Based Additive Manufacturing and its Mechanical and Microstructural Analysis

Metals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 775 ◽  
Author(s):  
Ali Waqas ◽  
Xiansheng Qin ◽  
Jiangtao Xiong ◽  
Hongbo Wang ◽  
Chen Zheng
Keyword(s):  
Additive Manufacturing ◽  
Gas Metal Arc Welding ◽  
Microstructural Analysis ◽  
Single Layer ◽  
Effective Area ◽  
Welding Parameters ◽  
Thin Wall ◽  
Optimization Of Process Parameters ◽  
Metal Arc Welding ◽  
Forming Characteristics

Additive manufacturing of metals using gas metal arc welding has an associated problem of variations of height in the onset and extinguishing parts of the weld bead. In this research, robot-assisted welding has been performed to investigate the problem, using AWS ER70S-6 low alloy steel welding electrode wire. After adjustment of welding parameters for a single-layer, single-pass, an optimal profile of welding energy was used to construct a thin wall which exhibited good forming characteristics with an effective area of approximately 97%. The resulting structure was ductile in nature with better tensile strength and microhardness as compared to the rolled steel available in industry with similar carbon content. The microstructure analysis revealed equiaxed grains in most parts of the structure having a fine grain size.

Numerical Modeling of Steel Surface Hardening in the Process of High Energy Heating by High Frequency Currents

2014 ◽  
Vol 698 ◽  
pp. 288-293 ◽  
Author(s):  
Vadim Yu. Skeeba ◽  
Vladimir Ivancivsky ◽  
Valeriy Pushnin
Keyword(s):  
Residual Stresses ◽  
High Frequency ◽  
Process Variations ◽  
Carbon Diffusion ◽  
Element Model ◽  
Hardened Layer ◽  
High Energy ◽  
Plastic Behavior ◽  
Heating Rates ◽  
Compressive Stresses

Surface layer modification methods using concentrated energy sources to ensure high heating rates of approximately 104 – 105 °C/s are becoming increasingly common in an attempt to improve operational performance of machine components. As a result, it is quite difficult to determine heat cycle parameters by means of experiments to predict the required intensity and distribution behavior of residual stresses and strains. The paper addresses the issue of numerical simulation of the stress-strain behavior during high energy heating by high frequency currents (HFC HEH). A finite element model has been generated using the ANSYS and SYSWELD software based on numerical computations of differential equations for transient heat conduction (Fourier equation), carbon diffusion (Fick's second law), and the elastic-plastic behavior of the material. The simulation data was verified by full-scale experiments using optical and scanning microscopy and mechanical and X-ray methods to determine residual stresses. It has been established that the level of residual compressive stresses on the component surface can be from-500 to-1000 MPa within the range of HFC HEH process variations under review. It is proven in theory and confirmed by experiments that the transition layer thickness must amount to 25 – 33 % of the hardened layer depth for the tensile stress peak to shift to deeper material layers while compressive stresses on the surface decrease by 6 – 10 %, in order to prevent hardening cracks.

Measurement of Residual Stresses in Stainless Steel Cladded Specimens

2010 ◽  
Author(s):  
E. Kingston ◽  
M. Udagawa ◽  
J. Katsuyama ◽  
K. Onizawa ◽  
D. J. Smith
Keyword(s):  
Stainless Steel ◽  
Residual Stresses ◽  
Steel Substrate ◽  
Single Layer ◽  
304 Stainless Steel ◽  
Hole Drilling ◽  
Stress Distributions ◽  
Compressive Stresses ◽  
Three Samples ◽  
Type 304

Residual stresses were measured in cladded steel specimens using deep hole drilling (DHD) and block removal and surface layering (BRSL) techniques. The samples consisted of a A533B steel substrate and cladded with Type 304 stainless steel using two different welding techniques; electro-slag (ESW) and submerged welding (SAW). Two SAW samples were created; one with a single layer of weld and a second with a double layer of welding. Only a single weld layer of ESW was used on another sample. All three samples were subjected to post-weld heat treatment prior to measurement. The measured residual stress distributions revealed (as expected) tensile stresses in the clad. However, the DHD method measured compressive stresses in the substrate adjacent to the clad for the single layer ESW and SAW welds. In contrast, the BRSL method found that the residual stresses in the substrate were close to zero or approximately tensile. The measurements are compared with results obtained from finite element (FE) simulations of the welding and PWHT treatment. The predicted tensile residual stresses in the clad were found to be larger than the measurements while in the substrate the FE analysis did not predict the measured compressive stresses.

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