## 3 Results and Discussion
### Areal Surface Texture Analysis  
The raw topography of AM components obtained using laser point interferometry is shown in Figure 7. The areal surface texture parameters \(Sa\) and \(Sz\) are calculated using equations given in ISO 25178. An issue arises while applying a suitable filtering value to analyze these surfaces. Usually, the filter is applied to separate the longer (understood as waviness) and shorter (understood as roughness) wavelengths from the measured data. Applying an improper filter will result in false quantifications. Therefore, the following sections discuss the effects of using various filtering values and their results. Figure 6: Percentage deviation in profile surface roughness results due to change in cut-off wavelength and evaluation length. (**a**) SLM; (**b**) DMLS; (**c**) EBM; (**d**) LENS. The resulting waviness and roughness areal surface topography of SLM specimen at various filtering conditions is shown in Figure 8. (Note that the discussions will be limited to analysis of the surface topography from the resulting contours. Future work will include an in-depth analysis of the Gaussian filter's effectiveness and transmission amplitude in the resulting contours). Figure 8a shows that the waviness topography is similar to the leveled raw profile shown in Figure 7a. For a filter of 0.025 mm, all the irregularities with a wavelength greater than 25 \(\upmu\)m (loose particles, partially melted and semi-welded structures) will be significantly present in the waviness profile, and the wavelengths less than 25 \(\upmu\)m would be significantly present in roughness topography. The waviness and roughness topography obtained by increasing the nesting index to 0.08 mm is shown in Figure 8b. In this case, all the irregularities with a wavelength greater than 80 \(\upmu\)m are present in the waviness topography (partial melts and semi-welded structures), and wavelength less than 80 \(\upmu\)m (loose particles) are present in roughness topography. Therefore, it can be said that the roughness topography indicates the presence of loose particles (wavelengths less than 80 \(\upmu\)m), and the waviness topography indicates the presence of partial melts and semi-welded structures (wavelengths greater than 80 \(\upmu\)m). Increasing the nesting index to the next larger value of 0.25 mm will have the same effect mentioned above on waviness and roughness topographies. In Figure 8c, the roughness topography would contain loose particles and partial melts; the waviness topography would contain the wavelengths due to semi-welded structures alone. The roughness topography in Figure 8d shows almost all the irregularities in the roughness topography as all the structures in the surface under study are significantly smaller than 800 \(\upmu\)m. Waviness topography contains wavelengths greater than 800 \(\upmu\)m (considered as a form error). A different set of filtering values were applied to the DMLS surface, and the resulting topographies are shown in Figure 9. Waviness topography (Figure 9a) is similar to the leveled raw profile as shown in Figure 7b as it contains all the irregularities with wavelengths greater than 25 \(\upmu\)m. Roughness topography (Figure 9b) contains errors due to the presence of loose particles (size < 80 \(\upmu\)m). Roughness topography (Figure 9c) contains errors due to the presence of loose particles, partial melts, and semi-welded structures (size < 250 \(\upmu\)m). Figure 8: Surface topography of as-built SLM surface after filtering. The only type of irregularity identified in the EBM surface is balling melts of approximately 80 \(\upmu\)m. The same effect of varying the filtering values applies even to the EBM surface. Roughness topography (Figure 10b) contains the wavelengths of irregularities due to balling melts (size \(<\) 80 \(\upmu\)m). One such limitation is that laser scanning cannot distinguish each ball melt separately as the balling melts in the surface entirely overlap.