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 Study on the origins of residual stresses in Ti-6Al-4V processed by additive manufacturing

2020 ◽  
Vol 321 ◽  
pp. 03001
Author(s):  
Nathan Dumontet ◽  
Benoit Malard ◽  
Bernard Viguier
Keyword(s):  
Additive Manufacturing ◽  
Energy Density ◽  
Residual Stresses ◽  
Dwell Time ◽  
Scanning Speed ◽  
Manufacturing Processes ◽  
Thermal Gradients ◽  
Laser Beam Melting ◽  
Reliable Parameter ◽  
Stress States

In additive manufacturing processes using laser beam melting high thermal gradients are generated, inducing residual stresses within the parts that may lead to deformations and, in worst cases, cracks. One of the materials that is the most sensitive to residual stresses is the Ti-6Al-4V alloy. In the present study, we focus on the various parameters that may control the genesis and build-up of the residual stress states. Dwell time and thermal conductivity, both influencing the heat evacuation, were studied. Higher thermal evacuation was find to rises residual stresses within the part. Then, the reliability of the energy density as a comparison parameter was investigated. Samples with the same energy densities but different power and scanning speed were elaborated. Energy density was shown as a non-reliable parameter to compare different processed parts.

scholarly journals Analytical Thermal Modeling of Metal Additive Manufacturing by Heat Sink Solution

Materials ◽  
2019 ◽  
Vol 12 (16) ◽  
pp. 2568 ◽  
Author(s):  
Jinqiang Ning ◽  
Daniel E. Sievers ◽  
Hamid Garmestani ◽  
Steven Y. Liang
Keyword(s):  
Heat Transfer ◽  
Finite Element Method ◽  
Boundary Condition ◽  
Finite Element ◽  
Additive Manufacturing ◽  
Computational Efficiency ◽  
Heat Sink ◽  
Thermal Gradients ◽  
Metal Additive ◽  
Element Method

Metal additive manufacturing can produce geometrically complex parts with effective cost. The high thermal gradients due to the repeatedly rapid heat and solidification cause defects in the produced parts, such as cracks, porosity, undesired residual stress, and part distortion. Different techniques were employed for temperature investigation. Experimental measurement and finite element method-based numerical models are limited by the restricted accessibility and expensive computational cost, respectively. The available physics-based analytical model has promising short computational efficiency without resorting to finite element method or any iteration-based simulations. However, the heat transfer boundary condition cannot be considered without the involvement of finite element method or iteration-based simulations, which significantly reduces the computational efficiency, and thus the usefulness of the developed model. This work presents an explicit and closed-form solution, namely heat sink solution, to consider the heat transfer boundary condition. The heat sink solution was developed from the moving point heat source solution based on heat transfer of convection and radiation. The part boundary is mathematically discretized into many heats sinks due to the non-uniform temperature distribution, which causes non-uniform heat loss. The temperature profiles, thermal gradients, and temperature-affected material properties are calculated and presented. Good agreements were observed upon validation against experimental molten pool measurements.

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.

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.

Residual Stress and Microstructural Variations in Thick Aluminium Alloy Forgings

2008 ◽  
Vol 571-572 ◽  
pp. 45-50 ◽  
Author(s):  
Jeremy S. Robinson ◽  
Christopher E. Truman ◽  
M.S. Hossain ◽  
Robert C. Wimpory
Keyword(s):  
Residual Stresses ◽  
Supersaturated Solid Solution ◽  
Cold Water ◽  
High Strength ◽  
Biaxial Compression ◽  
Hole Drilling ◽  
Second Phase ◽  
Thermal Gradients ◽  
The Core ◽  
Heat Treated

The most critical stage in the heat treatment of high strength aluminium alloys is the rapid cooling necessary to form a supersaturated solid solution. During cold water quenching of thick sections, the thermal gradients are sufficient to cause inhomogeneous plastic deformation which in turn leads to the development of large residual stresses. Two 215 mm thick rectilinear forgings made from 7075 and 7010 were heat treated, and the through thickness residual stresses measured by neutron diffraction and deep hole drilling. The distribution of residual stresses was found to be similar for both alloys varying from highly triaxial and tensile in the core to a state of biaxial compression in the surface. The 7010 forging exhibited significantly larger tensile stresses in the core. 7075 is a much more quench sensitive alloy when compared to 7010. This results in loss of supersaturation by second phase precipitation during quenching in the core of the 7075 forging.

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.

scholarly journals Local Thermal Rates and Gradients in Laser Powder Bed Fusion Metal Additive Manufacturing Method: Computer Simulation

2021 ◽  
Author(s):  
Hamed Hosseinzadeh
Keyword(s):  
Additive Manufacturing ◽  
Laser Power ◽  
Thermal Gradients ◽  
Powder Bed Fusion ◽  
Metal Powders ◽  
Powder Bed ◽  
Metal Additive Manufacturing ◽  
Scan Speed ◽  
Simulation Results ◽  
Metal Additive

The powder bed fusion (PBF) metal additive manufacturing (AM) method uses an energy source like a laser to melt the metal powders. The laser can locally melt the metal powders and creates a solid structure as it moves. The complexity of the heat distribution in laser PBF metal AM is one of the main features that need to be accurately addressed and understood to design and manage an optimized printing process. In this research, the dependency of local thermal rates and gradients on print after solidification (in the heat-affected zone) was numerically simulated and studied to provide information for designing the print process. The simulation results were validated by independent experimental results. The simulation shows that the local thermal rates are higher at higher laser power and scan speed. Also, the local thermal gradients increase if the laser power increases. The effect of scan speed on the thermal gradients is opposite during heating versus cooling times. Increasing the scan speed increases the local thermal gradients in the cooling times and decreases the local thermal gradients during the heating. In addition, these simulation results could be used in artificial intelligence (AI) and machine learning for developing digital additive manufacturing.

scholarly journals INVESTIGATION ON THERMAL DEFORMATION IN LASER ADDITIVE MANUFACTURING

2021 ◽  
Vol 2021 (3) ◽  
pp. 4584-4590
Author(s):  
Y. Kuroiwa ◽  
◽  
D. Kono ◽  
Y. Oda ◽  
◽  
...  
Keyword(s):  
Finite Element ◽  
Additive Manufacturing ◽  
Heat Source ◽  
Deformation Theory ◽  
Thermal Deformation ◽  
Finite Element Simulations ◽  
Laser Additive Manufacturing ◽  
Shape Accuracy ◽  
Metal Material ◽  
Metal Additive

In metal additive manufacturing, a metal material is melted by a concentrated heat source such as a laser. Therefore, thermal deformation occurs in the fabrication, which causes deterioration of shape accuracy and crack of the workpiece. In this study, a method to systematically reduce the thermal deformation was discussed. The mechanism of thermal deformation caused by stacking and lining up the bead was investigated using finite element simulations and experiments. Based on the obtained results and thermal deformation theory in welding, a method to reduce the thermal deformation was proposed and the validity of the method was demonstrated by simulation.

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