PSI - Issue 79

Daniela Neves et al. / Procedia Structural Integrity 79 (2026) 266–274

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1.1. Production Parameters Precise control of processing parameters is essential to minimise defects and to achieve the desired microstructure for each specific application. The production of components by SLM involves optimising several adjustable factors, such as laser parameters (power and scanning speed), powder characteristics (shape, composition, and size), build orientation, conditions of the processing atmosphere (type of inert gas, pressure, and flow), chamber temperature, laser scanning strategy, hatch distance, and layer thickness (Kurzynowski et al., 2012). The energy density (Ed), in J/m 3 , given by equation 1, is a factor that combines the most critical manufacturing parameters and describes the average energy applied per unit volume of material (Gong et al., 2013). = ×Pℎ× (1) Where P is the laser power [W], v is the laser scanning speed [m/s], h represents the hatch [m] spacing, and e denotes the layer thickness [m]. Additionally, SLM machines allow adjustment of processing parameters based on the position of the scan track within each layer. Such variation allows for improvements in the mechanical properties and overall quality of the final component. With respect to the track position, two designations are distinguished: Border, corresponding to a contour that surrounds the fill area — for example, Border, Following Border, and Hatch Vector — referring to its interior (Fig. 2).

Fig. 2 - Schematic Representation of the Scan Track positions in a layer

On the other hand, distinctions can also be made regarding the position of the layers: up-skin, in-skin, down-skin, core, and supports (Fig. 3-a). The term up-skin refers to the three upper layers of each region of the component, that is, those with surfaces facing upward (Manfredi et al., 2014). In contrast, the term down-skin refers to the lower layers (between one and four), facing downward, positioned on one or more supports or in contact with the powder. The use of supports is a common practice because these elements enable more effective heat dissipation and play an essential role in sustaining the part and counteracting the tensile forces that develop during the rapid cooling of the melt pools, which can lead to warping and delamination (Viale et al., 2022). Modern software (EOS EOSTATE, SLM Solution Layer Control System (LCS), Renishaw InfiniAM Spectral, GE Additive M-Flex Monitoring, etc.) enables automatic identification and assignment of these regions, enabling customisation of printing parameters. This functionality improves surface finishing. The remaining portion of the part is referred to as in-skin and corresponds to the side walls, located between the external surface and the internal core (Fig. 3-b). The core primarily represents the interior volume that is not in contact with external surfaces. In this region, parameters are generally applied that favour process efficiency and adequate material densification.