## 3 Results and Experimental Verification  
Figure 4 shows the distance between the specimen's surface and upper (\(U\)) and lower (\(L\)) end of the seam (a), as well as the seam width \(w\) (b). The results obtained with the OCT are colored, and the reference measurements obtained with thin cuts are black. Considering the reference values (black), the distance between the specimen's surface and the upper end of the seam \(U\) varies between 0.44 mm (\(E=0.35\) J/mm, \(z_{focus}=1.0\) mm) and 0.99 mm (\(E=0.30\) J/mm, \(z_{focus}=1.2\) mm) and the distance between surface and lower end L varies between 1.12 mm (\(E=0.14\) J/mm, \(z_{focus}=1.0\) mm) and 1.54 mm (\(E=0.46\) J/mm \(z_{focus}=1.2\) mm). The seam width \(w\) varies from 0.05 mm (\(E=0.16\) J/mm, \(z_{focus}=1.1\) mm) to 0.16 mm (\(E=0.43\) J/mm, \(z_{focus}=1.2\) mm). Shifting the focus and, therefore, the seam downward in the material decreases the seam height, whereas the width is nearly unaffected. Both seam height and width increase with increasing laser power. Considering the OCT measurements (colored), the weld seams with the highest and lowest energy are missing (except for \(z_{focus}=1.1\) mm). The processing of the missing weld seams is, in principle, possible but would require other image processing parameters. With other parameters, however, other seams would not be recognized. The maximum distances \(U\) and \(L\) at which OCT measurements were possible are 0.96 mm (\(E\) = 0.30 J/mm, \(z_{focus}\) = 1.2 mm) and 1.53 mm (\(E\) = 0.43 J/mm, \(z_{focus}\) = 1.2 mm). The average deviation between OCT and the reference measurement for the distance \(U\) is 0.025 \(\pm\) 0.021 mm, and the maximum is 0.08 mm (\(E\) = 0.30 J/mm, \(z_{focus}\) = 1.0 mm). For the distance \(L\), the average deviation is 0.034 \(\pm\) 0.05 mm and the maximum is 0.23 mm (\(E\) = 0.35 J/mm, \(z_{focus}\) = 1.1 mm). The height (\(L\) - \(U\)) of detectable seams is 0.26 mm (\(E\) = 0.19 J/mm, \(z_{focus}\) = 1.1 mm) to 0.87 mm (\(E\) = 0.35 J/mm, \(z_{focus}\) = 1.1 mm), and the width is 0.07 (\(E\) = 0.19 J/mm, \(z_{focus}\) = 1.1 mm) to 0.19 mm (\(E\) = 0.35 J/mm, \(z_{focus}\) = 1.1 mm). However, since this is the seam with the largest deviation by far, we also mention the second-largest seam with 0.78 mm height and 0.17 mm width (\(E\) = 0.43 J/mm, \(z_{focus}\) = 1.2 mm). The average deviation of the weld seam width \(w\) is 0.027 \(\pm\) 0.022 mm, and the maximum is 0.084 mm (\(E\) = 0.35 J/mm, \(z_{focus}\) = 1.2 mm). The seam width obtained with the OCT is always larger than the reference one. Our explanation for this is the melt squeeze out into the gap between the joining partners. This squeeze out was only evaluated as part of the weld seam in the OCT, but not in the thin cut measurements. It is possible to evaluate only the width without the melt blowout from the OCT data by, e.g., applying a fit to the detected contour. We intentionally included the squeezed material, as it will contribute to the weld seam's strength and can disturb the fluid channels of the manufactured part. The detection of the weld seam is not possible in every B-scan. Figure 5 shows the average distance in the feed direction (\(x\)) between two B-scans with successfully detected weld seams. The average distance between two consecutively detected weld seams is 0.04 mm, and the largest distance is 0.08 mm. Since the distance between two initially recorded B-scans is 0.0125 mm, this means that the automated weld seam identification successfully identifies seams in approximately 17% to 33% of B-scans. Figure 4: (**a**) Distance between specimens’ surface and upper (\(U\)) and lower (\(L\)) end of the seam as well as seam width \(w\) (**b**) in dependence of energy per unit length (\(E\)) at a 200 mm/s feed rate. Material: Ultramid B3S. Rayleigh length = 0.3 mm, \(\lambda\) = 1940 nm, \(\alpha\) = 0.8 1/mm. At least six welds per parameter setting were analyzed. The microtome data were obtained from [14].