A simplified analytical model of the laser powder bed fusion (LPBF) process was used to develop a novel density prediction approach that can be adapted for any given powder feedstock and LPBF system. First, calibration coupons were built using IN625, Ti64 and Fe powders and a specific LPBF system. These coupons were manufactured using the predetermined ranges of laser power, scanning speed, hatching space, and layer thickness, and their densities were measured using conventional material characterization techniques. Next, a simplified melt pool model was used to calculate the melt pool dimensions for the selected sets of printing parameters. Both sets of data were then combined to predict the density of printed parts. This approach was additionally validated using the literature data on AlSi10Mg and 316L alloys, thus demonstrating that it can reliably be used to optimize the laser powder bed metal fusion process.
Abstract:The laser powder bed fusion (L-PBF) technology was adapted for use with non-spherical economical water-atomized iron powders. A simplified numerical and experimental modeling approach was applied to determine-in a first approximation-the operation window for the selected powder in terms of laser power, scanning speed, hatching space, and layer thickness. The operation window, delimited by a build rate ranging from 4 to 25 cm 3 /h, and a volumetric energy density ranging from 50 to 190 J/mm 3 , was subsequently optimized to improve the density, the mechanical properties, and the surface roughness of the manufactured specimens. Standard L-PBF-built specimens were subjected to microstructural (porosity, grain size) and metrological (accuracy, shrinkage, minimum wall thickness, surface roughness) analyses and mechanical testing (three-point bending and tensile tests). The results of the microstructural, metrological and mechanical characterizations of the L-PBF-built specimens subjected to stress relieve annealing and hot isostatic pressing were then compared with those obtained with conventional pressing-sintering technology. Finally, by using an energy density of 70 J/mm 3 and a build rate of 9 cm 3 /h, it was possible to manufacture 99.8%-dense specimens with an ultimate strength of 330 MPa and an elongation to failure of 30%, despite the relatively poor circularity of the powder used.
The additive manufacturing (AM) process induces high uncertainty in the mechanical properties of 3D-printed parts, which represents one of the main barriers for a wider AM processes adoption. To address this problem, a new time-efficient microstructure prediction algorithm was proposed in this study for the laser powder bed fusion (LPBF) process. Based on a combination of the melt pool modeling and the design of experiment approaches, this algorithm was used to predict the microstructure (grain size/aspect ratio) of materials processed by an EOS M280 LPBF system, including Iron and IN625 alloys. This approach was successfully validated using experimental and literature data, thus demonstrating its potential efficiency for the optimization of different LPBF powders and systems.
Additive manufacturing (AM) technologies, such as laser powder bed fusion (LPBF), have gained significant attention because of their capacity to manufacture near-net shape complex metallic components. Although LPBF components can manifest static mechanical properties that are comparable to those of their wrought counterparts, processing-induced defects, such as porosity and lack of fusion, are regularly observed within the build and are of particular concern for the structural integrity of printed components. In this work, the impact of LPBF-induced defects on the static mechanical properties of Inconel 625 specimens is studied. To establish the relationship between the level of such defects and the specific combinations of LPBF parameters, coupons with porosities of up to 20% were manufactured by varying the laser power from 70 to 360 W, the scanning speed from 720 to 3840 mm/s, and the hatching space from 0.08 to 0.33 mm (a constant layer thickness of 40 microns was used). To measure the level of processing-induced porosity, the computed microtomography (micro-CT) and Archimedes' techniques were concurrently applied. The micro-CT also was used to evaluate the nature and morphology of defects and their distributions, resulting from different combinations of processing parameters. Next, tensile specimens with porosities of up to 3% with two build orientations (0° and 90°) were manufactured and subjected to stress relief annealing and hot isostatic pressing. The specimens then were tested to measure the impact of the prosessing-induced porosity, build orientation, and postprocessing conditions on the static mechanical properties of Inconel 625 specimens. Our results indicated that the presence of pores strongly reduces the ductility of the material, especially when stresses are applied along the build direction. Although hot isostatic pressing allowed a significant reduction in porosity, this postprocessing was ineffective in improving the ductility of specimens with as-printed porosities exceeding 0.3%.
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