5.1.1. Laser VED

The laser VED affects the number and volume of spatters. The formula for calculating laser VED is *E<sup>V</sup>* = *<sup>P</sup> Vdlh<sup>p</sup>* . In the formula, *P* is the laser power, *V* is the scanning velocity, *dl* is the laser diameter, and *h<sup>p</sup>* is the layer thickness of the powder [127]. Gunenthiram et al. [78] demonstrated that the volume of spatter increased with increasing the VED, as seen in Figure 22. Mumtaz et al. [128] used pulse shaping techniques to precisely regulate the energy of the laser–material interaction zone, minimizing the generated spatter during L-PBF, which improved the top surface roughness of the parts and minimized the melt pool width. Shi et al. [115] demonstrated that by adjusting the energy density during single-layer formation, the spatter defects can be successfully reduced. The sample with the smoothest surface was produced when the linear energy density and the surface energy density was applied to 0.4 J/mm to 0.6 J/mm and 4 J/mm<sup>2</sup> to 6 J/mm<sup>2</sup> , respectively.

• **Laser power:** The laser power applied affects the number and volume of spatters, in most situations, studies have shown that the higher the laser power input, the more severe the spatter behavior. Andani et al. [52] concluded that decreasing the laser power would reduce spatter in L-PBF, and the laser power dominates the effect on spatter generation. Chen et al. [46] demonstrated that adjusting the power intensity and distribution of the laser beam to maintain the melt pool temperature between the melting and boiling points can significantly reduce spatter generation.


**Figure 22.** On a 316L stainless steel powder bed, the effect of laser power and scanning velocity on large-sized spatter, For low laser powers (*P* = 220 W) and resulting VED values severe balling occurs, that generates important spattering. The lower amount of spatters is obtained for *P* values just above the balling threshold (*P* = 320 W, *V* = 0.54 m/s and 0.75 m/s). (Reprinted with permission from Ref. [78]. Copyright 2018 Elsevier B.V.). • **Laser power:** The laser power applied affects the number and volume of spatters, in **Figure 22.** On a 316L stainless steel powder bed, the effect of laser power and scanning velocity on large-sized spatter, For low laser powers (*P* = 220 W) and resulting VED values severe balling occurs, that generates important spattering. The lower amount of spatters is obtained for *P* values just above the balling threshold (*P* = 320 W, *V* = 0.54 m/s and 0.75 m/s). (Reprinted with permission from Ref. [78]. Copyright 2018 Elsevier B.V.).

most situations, studies have shown that the higher the laser power input, the more severe the spatter behavior. Andani et al. [52] concluded that decreasing the laser power would reduce spatter in L-PBF, and the laser power dominates the effect on

the cold spatter caused by entrainment.

duction, and component density.

melting and boiling points can significantly reduce spatter generation.

• **Scanning velocity:** The velocity of the laser scanning will affect the generation of spatter. Andani et al. [52] considered that increasing the laser scanning velocity would reduce spatter in L-PBF. Gunenthiram et al. [78] studied the number of spatters at different scanning velocities ( = 0.33 m/s~0.75 m/s) and found that the higher the scanning velocity, the less the number of hot spatters, as shown in Figure 22. However, a high scanning velocity leads to a longer scanning path, which increases

• **Laser diameter:** The laser spot size during L-PBF can significantly affect the melt dynamics and droplet spatter generation [117]. There are two reasons for the variation of the spot size: passive variation and active variation. For passive changes, the lens could be deformed due to thermal expansion and contraction induced by the incident high-energy laser, so that the spot size varies during laser conduction. The active variation is to adjust the spot size of the laser artificially. Gunenthiram et al. [78] demonstrated a possible way to entirely suppress the spatter by using a large spot when the melt pool is sufficiently deep. Sow et al. [116] investigated the influence of a large laser spot on L-PBF and concluded that combining a large spot with a low VED significantly improved the L-PBF in terms of the process stability, spatter re-

• **Layer thickness:** A high layer thickness results in a large amount of spatter. Schwerz et al. conducted experiments with layer thicknesses of 80 µm, 120 µm, and 150 µm, and found that the number of redeposited spatters increased with the layer thickness
