Laser Powder Bed Fusion of Water-Atomized Iron-Based Powders: Process Optimization

Abstract

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.

Optimization of Laser Powder Bed Fusion Processing Using a Combination of Melt Pool Modeling and Design of Experiment Approaches: Density Control

“…First, calculations of the LPBF melt pool dimensions were carried out using the analytical model of a semi-infinite solid with a moving Gaussian heat source [19]. This model has been successfully used for the determination of the LPBF processing parameters for pure iron [18] and Ti-Zr-Nb alloy [20]. The Gaussian model involves a symmetrical distribution of laser irradiance across the beam.…”

“…These FEM models take into account the optical penetration depth, the mass transfer-related phenomena, such as the Marangoni convection and the Rayleigh capillary flow, and the heat losses to the environment [11,29]. Secondly, the numerically predicted densities for pure iron and Ti-6Al-4V alloy powders are compared with their experimentally measured equivalents from [6] and [18]. The optimal processing windows for all these validation studies were obtained using the algorithm previously presented.…”

“…The reliability of the proposed processing optimization approach was then studied for Fe [18] and AlSi10Mg [35] powders. The density predictions were made using the physical properties of Table 5 and the processing maps are plotted in Figure 7a,b.…”

Edge and corner effects in selective laser melting of IN 625 alloy

“…Due to the high thermal gradients generated by the SLM process high levels of residual stress within the asbuilt part are encountered and usually post-treatment operations are required to avoid parts distortion [5]. Considering that more than 50 factors influence the melting [6,7] many negative effects can cause internal or surface defects in the manufactured parts such as: delamination and cracks, curling, warping, pores, undesired surface roughness or dimensional inaccuracy.…”

A Cold-Pressing Method Combining Axial and Shear Flow of Powder Compaction to Produce High-Density Iron Parts

“…Physical, mechanical, and chemical properties of powders, as well as the granulometry and morphology of particles, influence significantly on the formation of bonds between particles during perform compaction and further sintering. That affects the properties of the final product [7][8][9][10][11].…”