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 ◽  
...  

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.

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
A. V. Gusarov ◽  
I. Yadroitsev ◽  
Ph. Bertrand ◽  
I. Smurov

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.


2021 ◽  
Vol 68 ◽  
pp. 347-355
Author(s):  
Qihang Fang ◽  
Zhenbiao Tan ◽  
Hui Li ◽  
Shengnan Shen ◽  
Sheng Liu ◽  
...  

2020 ◽  
Vol 26 (5) ◽  
pp. 871-879 ◽  
Author(s):  
Haihua Wu ◽  
Junfeng Li ◽  
Zhengying Wei ◽  
Pei Wei

Purpose To fabricate a selective laser melting (SLM)-processed AlSi10Mg part with almost full density and free of any apparent pores, this study aims to investigate the effect of ambient argon pressure and laser scanning speed on the particles splash during the AlSi10Mg powder bed laser melting. Design/methodology/approach Based on the discrete element method (DEM), a 3D model of random distribution of powder particles was established, and the 3D free surface of SLM forming process was dynamically tracked by the volume of fluid, where a Gaussian laser beam acts as the energy source melting the powder bed. Through the numerical simulation and process experimental research, the effect of the applied laser power and scanning speed on the operating laser melting temperature was studied. Findings The process stability has a fundamental role in the porosity formation, which is process-dependent. The effect of the processing conditions on the process stability and the resultant forming defects were clarified. Research limitations/implications The results shows that the pores were the main defects present in the SLM-processed AlSi10Mg sample, which decreases the densification level of the sample. Practical implications The optimal processing parameters (argon pressure of 1,000 Pa, laser power of 180 W, scan speed of 1,000 mm/s, powder layer thickness of 35 µm and hatch spacing of 50 µm ) applied during laser melting can improve the quality of selective laser melting of AlSi10Mg, Social implications It can provide a technological support for 3D printing. Originality/value Based on the analysis of the pore and balling formation mechanisms, the optimal processing parameters have been obtained, which were argon pressure of 1,000 Pa, laser power of 180 W, scan speed of 1,000 mm/s, powder layer thickness of 35 µm and hatch spacing of 50 µm. Then, a near-fully dense sample free of any apparent pores on the cross-sectional microstructure was produced by SLM, wherein the relative density of the as-built samples is larger than 97.5%.


2021 ◽  
Vol 1027 ◽  
pp. 130-135
Author(s):  
Shuai Li ◽  
Bi Zhang ◽  
Cong Zhou

Selective laser melting (SLM) is a promising technique to build grinding wheels with complex structures. In this paper, Ni-based self-fluxing alloys are chosen as bond materials to investigate single track formation on a steel substrate under different processing parameters. Results show that irregular and balling tracks are obtained with a low linear energy density (LED). The width of a melt pool increases linearly with LED. For LED values larger than around 0.9 J/mm, keyhole occurs in the melt pool, which is not desirable in the SLM process. Energy dispersive spectroscopy (EDS) mapping is performed to investigate the formation of the melt pool. Through an analysis on chemical distributions, it is found that the melt pool has a mixture of the partly melted substrate and powders. However, in the keyhole region, only the alloying elements of the substrate are detected due to the repulsion of the melted powder materials caused by the recoil pressure. This work can offer guidance on parameter optimization for the fabrication of SLMed grinding wheels.


2011 ◽  
Vol 189-193 ◽  
pp. 3668-3671 ◽  
Author(s):  
Qing Song Wei ◽  
Xiao Zhao ◽  
Li Wang ◽  
Rui Di Li ◽  
Jie Liu ◽  
...  

Selective Laser Melting (SLM) can produce high-performance metal parts with complex structures. However, it’s difficult to control the processing parameters, because many factors involves. From the perspective of the molten pool, the study focuses on the effects of processing parameters, including scanning speed, laser power, scanning space, layer thickness, and scanning strategies, on the surface quality, the balling effect, the density of SLM parts, by conducting experiments of single track, single layer and block forming. The results show that the quality of the molten pool is affected by laser power and scanning speed. Scanning drove in the strategy of “jumping and turning”,a smooth surface and a less balling effect will be obtained. The thicker the powder layer is, the lower density will be obtained. The optimal parameters from series of experiments are: laser power of 98W; scanning speed of 90mm/s; scanning space of 0.07mm; layer thickness of 0.1mm; and scanning strategy of “jumping and turning”.


Author(s):  
Chong Teng ◽  
Haijun Gong ◽  
Attila Szabo ◽  
J. J. S. Dilip ◽  
Katy Ashby ◽  
...  

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.


Author(s):  
Bo Cheng ◽  
Subin Shrestha ◽  
Y. Kevin Chou

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.


2016 ◽  
Vol 51 (4) ◽  
pp. 519-532 ◽  
Author(s):  
Jiubin Jue ◽  
Dongdong Gu

The advanced selective laser melting technology was employed to prepare in situ Al based composites. Relationship among selective laser melting processing parameters, microstructures and resultant mechanical properties had been established. It turned out that in situ Al2Si4O10/Al composites were successfully fabricated by selective laser melting of Al2O3/AlSi10Mg composite powders. Due to the overlap between neighboring tracks and the remelting of previously solidified layers, two distinguished zones consisting of track core and track overlap were produced in laser induced melt pool. The two zones, respectively experienced different thermal histories, thus leading to the variation of cooling rate, which had a significant influence on the microstructural development and resultant mechanical performances. The track core mainly consisted of remarkably refined cellular dendritic Al matrix decorated with uniformly distributed ring-structured Al2Si4O10 reinforcements, while the track overlap was characterized with comparatively coarse columnar dendritic Al matrix as well as the coarse Al2Si4O10 reinforcements. At the optimal v of 500 mm/s, the obtained dynamic nanohardness ( H d) of track core ( H d = 3.79 GPa) and track overlap ( H d = 3.52 GPa) for selective laser melting processed composites part both showed tremendous enhancement upon that of unreinforced Al part ( H d = 0.58 GPa). The dry sliding wear tests indicated that the optimally prepared Al2Si4O10/Al composites part exhibited excellent wear performance with a considerably low coefficient of friction of 0.32 and a significantly reduced wear rate of 4.52 × 10−5 mm3 N−1 m−1. The formed consecutive protective adherent tribolayer on the worn surface and the significantly enhanced hardness of the composites well accounted for the superior wear performance.


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