## 1 Introduction  
In order to meet industrial requirements, additive manufacturing can be seen as a technology for various applications and a production alternative to common manufacturing processes [1, 2]. Following on from initial applications, such as functional prototyping, this technology is now capable of producing high quality parts at low costs, in fast delivery times, in a highly repeatable way, and in different materials, from plastics to high strength titanium alloys [3]. Recent trends in additive manufacturing feature a wide range of research fields [4], such as microstructural applications [5], electronic devices [6], and feedstock material [7], for automotive, aerospace, and medical use cases [8]. In [9], [PERSON] et al. discuss a wide range of use cases and the main contributions of this technology to overcoming the worldwide COVID-19 pandemic from the perspective of the adaptability of materials and applications. Supply shortages of personal protective equipment such as face shields and mask straps were overcome, and previously unavailable ventilator connectors were manufactured within a short period of time. In terms of research and development, laser-based powder bed fusion of polymers (PBF-LB/P) has experienced significant growth over the last decade. In this selective laser sintering (SLS) process, a high energy laser merges material at selected areas on the powder bed surface. Heat treatment below the melting point leads to the formation and growth of sintering bridges between powder particles and densification of the material without liquefaction. After laser exposure and a period of cooling, a new layer of powder is applied by the coater and the build platform is lowered by the thickness of one layer. Constant continuation of these process segments enables the formation of solid and three-dimensional structures, enclosed by non-melted powder [10; 11]. The schematic of the PBF-LB/P process is depicted in Figure 1.  
As described in [13; 14], the processing temperature of semi-crystalline thermoplastics in PBF-LB/P is based on the model of isothermal laser sintering by differential scanning calorimetry (DSC) measurements. The DSC curve depicted in Figure 2 shows the heat flux contrasted with process temperature and thermal transitions of PA12 (PA2200, EOS GmbH). As can be seen in Figure 2, the inside temperature of the building chamber has to exceed the recrystallization temperature \(T_{ic}\) and be lower than the temperature of melting \(T_{im}\). The simultaneous existence of a solid and molten state allows solidification without thermal distortion and thermal stress, due to the charact  
Figure 1: The schematic of selective laser sintering [12]. Figure 2: DSC (differential scanning calorimetry) curve of melting and recrystallization process in selective laser sintering of PA12 [13]. process. The molten state lasts until the building step's completion and the subsequent recrystallization happens homogeneously due to the low cooling rate. Many factors, such as complex thermal interactions during the building step, the involvement of the continuously repeating sub-processes of powder coating, laser exposure, and consolidation affect the process of selective laser sintering [15]. Uncontrolled thermal interactions are especially likely to affect the workpiece's properties, such as its dimensional accuracy, mechanical properties, and part density. Further investigations of temperature fields are required as part of process monitoring to understand thermal interactions, ensure part quality, and decrease the number of defects [16]. By meeting industrial requirements, the process of laser-based powder bed fusion of polymers (PBF-LB/P) has already broken through in certain fields. However, successful integration into the industrial process flow and into the supply chain is still challenged by the lack of sustainable process control [17]. Consistent process performance would require suitable in-process quality assurance measurements.