PSI - Issue 77

A. Polanský et al. / Procedia Structural Integrity 77 (2026) 529–536 Adam Polanský / Structural Integrity Procedia 00 (2026) 000 – 000

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Boschetto and colleagues performed defect segmentation using hysteresis thresholding with morphological preprocessing. Lately, they evaluated the influence of detected defects on the printed part in terms of height and showed a correlation with actual defects [14]. 3. Layer Quality Influence The quality of each layer is essential to ensure mechanical properties. Here, the most important factors are introduced. Starting with the condition of the metal powder. According to Svozilová et al, there are differences between virgin, used, and recycled powder. Significant differences were measured in microhardness, chemical composition, and flowability of metal powder, which is critical for the correct spreading of a new layer [15]. Powder quality is closely related to the type of recoater blade used. Generally, hard blades create denser layers, while brush or polymer blades create less dense ones. Horn et. al found that the type of recoater blade has no effect on Inconel 718 [16]. Nevertheless, Shamsdini et al. measured rapidly different ductility for maraging steel 18Ni300 using a hard and a brush blade, despite the same tensile strength and hardness. This was caused by different amounts of residual austenite [17]. Scattering is a phenomenon in which non-melted particles are ejected from the melt pool and possibly redeposit on the part surface. They may contaminate the powder or be captured by the recoater and create scratches. Zhang et al. observed increased surface roughness when unmelted particles were present in the sintered powder. That in turn weakens inter-layer bonding. The spatter formation is highly related to the laser parameters, the position of the part on the building platform, or the gas flow [18].

Fig. 2. (a) visible waves caused by recoater vibrations (b) recoater streaking caused by recoater blade damage (c) missing powder caused by support structure geometry

In this work, we focus on monitoring defects that occur during powder spreading, which leads to visible areas of inhomogeneous layer thickness. The most common defect is when the recoater collides with a part due to its incorrect positioning or thermal expansion, resulting in a visible pattern of different layer heights called waves, see Fig.2 (a). These collisions possibly damage the recoater blade by chipping small pieces off, which in turn creates