Model of Radiation and Heat Transfer in Laser-Powder Interaction Zone at Selective Laser Melting

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
A. V. Gusarov ◽  
I. Yadroitsev ◽  
Ph. Bertrand ◽  
I. Smurov
Keyword(s):  
Laser Beam ◽  
Selective Laser Melting ◽  
Metallic Powder ◽  
Single Line ◽  
Powder Layer ◽  
Width Ratio ◽  
Beam Diameter ◽  
Laser Melting ◽  
Scanning Velocity ◽  
Melt Pool

A model for coupled radiation transfer and thermal diffusion is proposed, which provides a local temperature field. Single-line scanning of a laser beam over a thin layer of metallic powder placed on a dense substrate of the same material is studied. Both the laser beam diameter and the layer thickness are about 50 μm. The typical scanning velocity is in the range of 10–20 cm/s. An effective volumetric heat source is estimated from laser radiation scattering and absorption in a powder layer. A strong difference in thermal conductivity between the powder bed and dense material is taken into account. The above conditions correspond to the technology of selective laser melting that is applied to build objects of complicated shape from metallic powder. Complete remelting of the powder in the scanned zone and its good adhesion to the substrate ensure fabrication of functional parts with mechanical properties close to the ones of the wrought material. Experiments with single-line melting indicate that an interval of scanning velocities exists, where the remelted tracks are uniform. The tracks become “broken” if the scanning velocity is outside this interval. This is extremely undesirable and referred to as the “balling” effect. The size and the shape of the melt pool and the surface of the metallurgical contact of the remelted material to the substrate are analyzed in relation to the scanning velocity. The modeling results are compared with experimental observation of laser tracks. The experimentally found balling effect at scanning velocities above ∼20 cm/s can be explained by the Plateau–Rayleigh capillary instability of the melt pool. Two factors destabilize the process with increasing the scanning velocity: increasing the length-to-width ratio of the melt pool and decreasing the width of its contact with the substrate.

scholarly journals Uncertainties Induced by Processing Parameter Variation in Selective Laser Melting of Ti6Al4V Revealed by In-Situ X-ray Imaging

Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 530
Author(s):  
Zachary A. Young ◽  
Meelap M. Coday ◽  
Qilin Guo ◽  
Minglei Qu ◽  
S. Mohammad H. Hojjatzadeh ◽  
...  
Keyword(s):  
Laser Beam ◽  
Selective Laser Melting ◽  
Small Deviation ◽  
Processing Parameters ◽  
Powder Layer ◽  
Beam Size ◽  
Processing Parameter ◽  
Laser Melting ◽  
Melt Pool

Selective laser melting (SLM) additive manufacturing (AM) exhibits uncertainties, where variations in build quality are present despite utilizing the same optimized processing parameters. In this work, we identify the sources of uncertainty in SLM process by in-situ characterization of SLM dynamics induced by small variations in processing parameters. We show that variations in the laser beam size, laser power, laser scan speed, and powder layer thickness result in significant variations in the depression zone, melt pool, and spatter behavior. On average, a small deviation of only ~5% from the optimized/reference laser processing parameter resulted in a ~10% or greater change in the depression zone and melt pool geometries. For spatter dynamics, small variation (10 μm, 11%) of the laser beam size could lead to over 40% change in the overall volume of the spatter generated. The responses of the SLM dynamics to small variations of processing parameters revealed in this work are useful for understanding the process uncertainties in the SLM process.

Numerical Investigation of Selective Laser Melting Process for 904L Stainless Steel

2012 ◽  
Author(s):  
Miranda Fateri ◽  
Andreas Gebhardt ◽  
Maziar Khosravi
Keyword(s):  
Heat Flux ◽  
Stainless Steel ◽  
Selective Laser Melting ◽  
Melting Process ◽  
Full Density ◽  
Laser Melting ◽  
Scanning Velocity ◽  
Selective Laser Melting Process ◽  
Fine Mesh ◽  
Melt Pool

Selective Laser Melting process (SLM) is an important manufacturing method for producing complex geometries which allows for creation of full density parts with similar properties as the bulk material without extensive post processing. In SLM process, laser power, beam focus diameter, and scanning velocity must be precisely set based on the material properties in order to produce dense parts. In this study, Finite Element Analysis (FEA) method is employed in order to simulate and analyze a single layer of 904L Stainless Steel. A three-dimensional transient thermal model of the SLM process based on phase change enthalpy, irradiation scattering, and heat conductivity of powder is developed. The laser beam is modeled as a moving heat flux on the surface of the layer using a fine mesh which allows for a variation of the shape and distribution of the beam. In this manner, various Gaussian distributions are investigated and compared against single and multi-element heat flux sources. The melt pool and temperature distribution in the part are numerically investigated in order to determine the effects of varying laser intensity, scanning velocity as well as preheating temperature. The results of the simulation are verified by comparing the melt pool width as a function of power and velocity against the experimentally obtained results. Lastly, 3D objects are fabricated with a SLM 50 Desktop machine using the acquired optimized process parameters.

scholarly journals Beam Diameter Dependence of Performance in Thick-Layer and High-Power Selective Laser Melting of Ti-6Al-4V

Materials ◽  
2018 ◽  
Vol 11 (7) ◽  
pp. 1237 ◽  
Author(s):  
Wentian Shi ◽  
Yude Liu ◽  
Xuezhi Shi ◽  
Yanjun Hou ◽  
Peng Wang ◽  
...  
Keyword(s):  
Selective Laser Melting ◽  
High Power ◽  
Large Diameter ◽  
Thick Layer ◽  
Beam Diameter ◽  
Laser Melting ◽  
Power Laser ◽  
Beam Laser ◽  
Melt Pool ◽  
Thick Layers

A 400 W high-power laser was used to fabricate 200-µm-thick Ti-6Al-4V samples to evaluate the effects of small (50 μm) and large (200 μm) beam diameter on density, microstructure and mechanical properties. A series of single-track experiments demonstrated that it was challenging for the small-beam laser to fabricate smooth and defect-free scan tracks. A larger beam diameter efficiently avoided process instability and provided a more stable and uniform melt pool. By increasing the beam diameter, the density of multilayer samples reached 99.95% of the theoretical value, which is much higher than that achieved with the small beam diameter. However, it was difficult to completely eliminate defects due to serious spatter and evaporation. Moreover, all of the generated samples had relatively coarse surfaces. For the large beam diameter of 200 µm, the optimal yield strength, ultimate tensile strength and elongation were 1150 MPa, 1200 MPa and 8.02%, respectively. In comparison, the small beam diameter of 50 µm resulted in values of 1035 MPa, 1100 MPa and 5.91%, respectively. Overall, the large-diameter laser is more suitable for high-power selective laser melting (SLM) technology, especially for thick layers.

Simulating Melt Pool Shape and Lack of Fusion Porosity for Selective Laser Melting of Cobalt Chromium Components

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Chong Teng ◽  
Haijun Gong ◽  
Attila Szabo ◽  
J. J. S. Dilip ◽  
Katy Ashby ◽  
...  
Keyword(s):  
Selective Laser Melting ◽  
Defect Formation ◽  
Powder Layer ◽  
Complex Object ◽  
Cobalt Chromium ◽  
Laser Melting ◽  
Design Modification ◽  
Lack Of Fusion ◽  
Melt Pool ◽  
Geometrically Complex

Cobalt chromium is widely used to make medical implants and wind turbine, engine and aircraft components because of its high wear and corrosion resistance. The ability to process geometrically complex components is an area of intense interest to enable shifting from traditional manufacturing techniques to additive manufacturing (AM). The major reason for using AM is to ease design modification and optimization since AM machines can directly apply the changes from an updated STL file to print a geometrically complex object. Quality assurance for AM fabricated parts is recognized as a critical limitation of AM processes. In selective laser melting (SLM), layer by layer melting and remelting can lead to porosity defects caused by lack of fusion, balling, and keyhole collapse. Machine process parameter optimization becomes a very important task and is usually accomplished by producing a large amount of experimental coupons with different combinations of process parameters such as laser power, speed, hatch spacing, and powder layer thickness. In order to save the cost and time of these experimental trial and error methods, many researchers have attempted to simulate defect formation in SLM. Many physics-based assumptions must be made to model these processes, and thus, all the models are limited in some aspects. In the present work, we investigated single bead melt pool shapes for SLM of CoCr to tune the physics assumptions and then, applied to the model to predict bulk lack of fusion porosity within the finished parts. The simulation results were compared and validated against experimental results and show a high degree of correlation.

scholarly journals Numerical-Experimental Study of the Consolidation Phenomenon in the Selective Laser Melting Process with a Thermo-Fluidic Coupled Model

Materials ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 1414 ◽  
Author(s):  
Francisco Cordovilla ◽  
Ángel García-Beltrán ◽  
Miguel Garzón ◽  
Diego Muñoz ◽  
José Ocaña
Keyword(s):  
Selective Laser Melting ◽  
Coupled Model ◽  
Melting Process ◽  
Metallic Powder ◽  
Added Value ◽  
Limiting Factors ◽  
Powder Layer ◽  
Laser Melting ◽  
Selective Laser Melting Process ◽  
Eulerian Formulation

One of the main limiting factors for a widespread industrial use of the Selective Laser Melting Process it its lack of productivity, which restricts the use of this technology just for high added-value components. Typically, the thickness of the metallic powder that is used lies on the scale of micrometers. The use of a layer up to one millimeter would be necessarily associated to a dramatic increase of productivity. Nevertheless, when the layer thickness increases, the complexity of consolidation phenomena makes the process difficult to be governed. The present work proposes a 3D finite element thermo-coupled model to study the evolution from the metallic powder to the final consolidated material, analyzing specifically the movements and loads of the melt pool, and defining the behavior of some critical thermophysical properties as a function of temperature and the phase of the material. This model uses advanced numerical tools such as the Arbitrary Lagrangean–Eulerian formulation and the Automatic Remeshing technique. A series of experiments have been carried out, using a high thickness powder layer, allowing for a deeper understanding of the consolidation phenomena and providing a reference to compare the results of the numerical calculations.

Preliminary Testing of Temperature Measurements in Selective Laser Melting

2017 ◽  
Author(s):  
Bo Cheng ◽  
Stephen Cooke ◽  
Y. Kevin Chou
Keyword(s):  
Selective Laser Melting ◽  
Full Density ◽  
Beam Power ◽  
True Temperature ◽  
Width Ratio ◽  
Process Conditions ◽  
Thermal Imager ◽  
Laser Melting ◽  
Melt Pool ◽  
Length Width

Selective laser melting (SLM) based on added-material manufacturing method is one of the Additive Manufacturing (AM) technologies that can build full density metallic components. In this study, a thermal imager with about 670 nm wavelength was employed to collect build surface process temperature information during SLM fabrication using Monel K500 powder. The major findings are as follows. (1) At nominal process conditions of 600 mm/s beam speed and 180 W beam power, the melt pool has a length of about 0.6 mm and a width of about 0.36 mm. (2) The obtained melt pool length/width ratio is about 1.5 for different build height. With the increase of build height, no clear trend was observed for melt pool length/width ratio and melt pool length value. (3) It is difficult to obtain true temperature in this study but it is possible to estimate melt pool dimension with the identified radiant liquidus temperature.

The Mechanism of Forming Coagulated Particles in Selective Laser Melting of Cobalt-Chromium-Molybdenum Powder

2020 ◽  
Vol 839 ◽  
pp. 79-85 ◽  
Author(s):  
Alexander A. Saprykin ◽  
Yuriy P. Sharkeev ◽  
Natalya A. Saprykina ◽  
Egor A. Ibragimov
Keyword(s):  
Selective Laser Melting ◽  
Powdered Material ◽  
Beam Diameter ◽  
Molybdenum Powder ◽  
Cobalt Chromium ◽  
Laser Melting ◽  
Movement Velocity ◽  
Scanning Velocity ◽  
Preheating Temperature ◽  
Cobalt Chromium Molybdenum

Selective laser melting (SLM) is thought to be a prospective manufacturing technology of complex metal components. Formation of coagulated particles when melting is reported to be an important factor for target mechanical properties of the end product. This paper discusses the effect of SLM parameters, including laser output power, laser movement velocity, preheating temperature of the powder, laser beam diameter on the mechanism of forming coagulated particles in melting cobalt-chromium-molybdenum powdered material. The study shows that a rise of power to 60 W at a scanning velocity 6 mm/s causes coagulated particles to expand to 350 μm; that is far bigger than a size of powder in as delivered state (90 μm). The work investigates the effect of mechanical activation of cobalt-chromium-molybdenum powder on dimensions of coagulated particles. The research data can be applied to the improvement of up-to-date optimization approaches to manufacturing process parameters in SLM technology.

Stress and Deformation Evaluations of Scanning Strategy Effect in Selective Laser Melting

2016 ◽  
Author(s):  
Bo Cheng ◽  
Subin Shrestha ◽  
Y. Kevin Chou
Keyword(s):  
Residual Stresses ◽  
Laser Beam ◽  
Selective Laser Melting ◽  
High Energy ◽  
Powder Layer ◽  
Stress Difference ◽  
Laser Melting ◽  
Scanning Strategy ◽  
Scanning Pattern ◽  
Stress And Deformation

Selective laser melting (SLM) is one of the Additive manufacturing (AM) processes that can build physical part in an added material method from digital data. In such a process, computer designed part model will be decomposed into hundreds of thousands of layers. The layered information is then transferred to SLM equipment and the part is built in a layer by layer fashion. Each powder layer will be scanned and melted in the required region by a high energy laser beam in a given scanning pattern so as to form a desired geometry. Finally, fully functional parts can be produced by repeatedly powder deposition, melting and solidification process. This process offers numerous advantages such as tooling-free productions and design freedom in geometry. In addition, SLM process is quite suitable for complicated parts such as customer designed medical implants and internal channels which are difficult to manufacture by conventional methods such as casting and machining. However, the localized heating and cooling process can lead to defects such as high residual stress, part distortion or delamination failure in SLM fabricated parts. These potential defects may impede the wide application of this technology. It is known that the laser beam scanning path will affect the thermomechanical behaviors of the build part, and thus, altering the scanning pattern may be a feasible strategy to reduce residual stresses and deformations by influencing the heat intensity input distribution. In this study, a 3D sequentially coupled finite element method (FEM) model, incorporating a volumetric moving Gaussian heat source, powder as well as solid material temperature dependent properties and layer addition features, was developed to study the complex thermomechanical process of SLM. The model was applied to evaluate six different scanning strategies effect on part temperature, stress and deformation. The major results have been summarized as follows. (1) Among all cases tested, the out-in scanning pattern has the maximum stresses along the X and Y directions; while the 45 degree inclined scanning may reduce residual stresses in both directions. (2) Large directional stress difference can be caused by back and forth line scanning strategy while minor directional stress difference is observed for other tested cases. (3) X and Y directional stress concentration is shown around the edge of deposited layers and the interface between deposited layers and substrate for all cases. (4) The 45 degree inclined scanning case has the smallest build direction deformation while the in-out scanning case has the largest deformation among the tested cases.

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