Investigation of Scanning Strategies and Laser Remelting Effects on Top Surface Deformation of Additively Manufactured IN 625

Abstract

The main drawbacks of the Laser Powder Bed Fusion (LPBF) process are the surface quality and dimensional accuracy of manufactured parts due to the edge and corner effects. These effects can be diminished by using an appropriate balance of the process parameters and scanning strategies. This paper focuses on the assessment of reducing the edge and corner effects that occur in additively manufactured IN 625 alloy via the LPBF technique by varying the hatch angle rotation (by 45°, 67°, and 90°) and volumetric energy density (VED), and using the laser top surface remelting technique (LSR). The edge and corner effects of the cubic samples were quantitatively evaluated on the top surface by 3D laser surface scanning. It was found that the edge and corner effects became more pronounced in the cases of samples built with no contour and hatch angles of 45° and 67°, while the smallest deformations were obtained when the hatch angle was rotated by 90°. Moreover, the heights of both the edge and corner ridges increase as the number of remeltings passing the top layer increases. Conversely, when a lower VED was used for melting the top layer(s) of the samples, the edge and corner ridges were slightly reduced.

Assessment of Residual Stresses in Laser Powder Bed Fusion Manufactured IN 625

“…During rapid solidification, the elevated ridges become more prominent, especially in the cases of samples built with the 67 • and chessboard scanning strategies. This adverse effect is primarily attributed to compressive stress around the corners and the thermal warping effect [37,38], which can lead to significant distortions in additively manufactured components [36]. As seen in Figures 6-9, the distortions of bridge pieces become more pronounced after the removal from the base plate (after cut).…”

“…These factors are directly influenced by the pattern, where the scan could be an entire layer, separated islands, or a stripe in the chessboard. Although 90 • , 45 • , and 67 • are commonly used hatch angles for bi-directional scanning, a previous study on top surface deformation of AMed IN 625 demonstrated that the differences in terms of edge width and height between 90 • and 67 • angles are relatively close, while the hatch angle of 45 • induces the highest deformations [36].…”

“…These findings are consistent with previous research on IN 625 manufactured via the PBF-LB/M technique. In a previous study [36], a parallel investigation was conducted on the top surface deformation of IN 625 cubes manufactured using similar manufacturing and characterization conditions, process parameters, and identical equipment. This study explored various factors, including the presence or absence of a contour strategy, different hatch angle rotations, reductions in volumetric energy density (VED) for the last layer(s) of parts, and remelting the last layer once or several times.…”

“…The findings from this study revealed that IN 625 samples built with hatch angle rotations of 45 • and 67 • had 72% and 20% higher deformations, respectively, compared to those built with a rotation angle of 90 • between successive layers. Notably, a 90 • hatch angle rotation induces a checkerboard pattern due to epitaxial solidification, resulting in reduced deformation in PBF-LB/M components compared to the 45 • and 67 • hatch angle rotations, leading to a hexagonal grain orientation [36]. Introducing the contour strategy, the corner height of samples built with hatch angles of 45 • , 67 • , or 90 • were reduced by 17%, 31%, and 19%, respectively, compared to the same samples without contour.…”

“…Also, the samples were built with no contour strategy. Prior studies conducted by the authors [33][34][35][36] demonstrated that these parameters are optimal in terms of the density, microstructure, and mechanical properties of the IN 625 alloy manufactured using the same Lasertec 30 SLM machine. This approach was adopted to facilitate a more precise understanding of the isolated impact of scanning strategies on the results, independent of other variables.…”