## 4 Discussion  
This paper proposes an approach of real-time process monitoring and in situ defect detection in PBF-LB/P by the simultaneous application of industrial grade laser profilometry and thermal imaging. As the main part of this study, the 3D mapping of the entire powder bed surface inside the installation space and the representation of the related temperature fields were successfully realized for the first time. Correlations of thermal distributions and the influences on metrics such as powder layer quality, curling height, and associated melting depth were revealed by gathering data on structural height maps. The resulting data provided by the two different sensor concepts was considered individually to derive independent results as well as simultaneously synchronized to confirm correlations. The modified settings on the thermal color map and the depicted temperature range enabled the verifiable visualization of artificially created curling failures in the powder bed of an EOS Formiga P 110 laser sinter system. The adaption of the process by lowering the temperature to 97% and iteratively extending the layer cooling time, which is usually related to the internal exposure strategy, enabled the simulation of curling within different degrees of intensity and at several process stages such as post-coating and pre-coating after laser exposure. The visibility of curling failure and related temperature fields at coated and non-coated areas of the build parts demonstrated that the thermal conductivity changes within phase transition of powder to solid. In order to confirm the height differences indicated by the thermal recordings due to lifting of parts from the powder bed, the radiometric output data of the laser profilometer were analyzed at equal time steps of process progression. The linear translation of the laser profilometer generated 3D height maps, highlighting structural failures by measuring the complete powder bed surface inside the installation space. Considering both sets of data, an exact match of curling locations on the thermal images and on the 3D topology maps  
Figure 17: The cross section of the build part in the xz-plane after laser exposure. The transition area occurs between the actual part and the surrounding powder bed. (**a**) shows the process state without lifting of free edges with L\({}_{Z}\) as current layers and h\({}_{\text{m}}\) as melting depth. (**b**) shows the current process state with curling and thus a resulting calculation of height peaks. was confirmed, which further establishes the verifiable detection of curling failures by thermal imaging. The analysis of the profile sections on the xz-plane revealed the exact progression of curling height in relation to the powder bed surface as a reference plane, including peak values as transition points from curled parts to the powder bed surface, starting at 23 \(\upmu\)m to a maximum value of 560 \(\upmu\)m. The direct comparison of measured curling behavior at pre- and post-coating states indicated the development of a transition area at peripheral zones of build parts, resulting in partly melted powder sticking to the components, leading to additional peaks on top of the of the components. The effective curling height (ECH) after laser exposure was verified as the sum of the actual height h\({}_{1}\) of part lifting and the additional height h\({}_{2}\) of adherent partly molten powder particles and material affected by the capillarity effect as described in [51]. Further effects were observed, such as measured warpage of the part center in the negative z direction, induced by the creation of tensile stresses on the top and compressive stresses on the bottom of parts, as previously theoretically described by [PERSON] and [PERSON] in [48] and by [PERSON] in [17]. This work does not consider the effects of powder cake cooling and crystallization kinetics on further distortion effects and mechanical properties of the finished parts. In [52], [PERSON] et al.